ثانوية أرشيف بنك الأسئلة المدونة

Magnetic Effect of Electric Current (continued) questions

Physics · 3rd secondary (languages) · Electric Current and Electromagnetism · Magnetic Effect of Electric Current and Measuring Instruments

Question bank for the lesson "Magnetic Effect of Electric Current (continued)" with 171 questions. Pick a set and start: you see at once whether your answer is right and read the explanation. Free, no sign-up.

Lesson questions

Click any question to solve it on the site and see the answer with its explanation.

Multiple choice questions

  1. Which of the following figures correctly shows the pattern of magnetic flux lines produced by a direct current flowing in a circular metal loop?

    Figure of question 1
    1. A A
    2. B B
    3. C C
    4. D D
    Solve this question →

  2. A circular metal loop carries an electric current in the direction shown in the figure. Which of the following directions is the direction of the magnetic field at the centre of the loop due to the current?

    Figure of question 2
    1. A The positive x-axis
    2. B The positive z-axis
    3. C The negative x-axis
    4. D The negative y-axis
    Solve this question →

  3. In the opposite figure, a circular loop of radius 10 cm carries a current of 5 A. The magnetic flux density at the centre of the loop (c) and its direction are .......... (given: π = 3.14)

    Figure of question 3
    1. A 2.6×10−52.6 \times 10^{-5} T, perpendicular to the page and outwards
    2. B 3.14×10−53.14 \times 10^{-5} T, perpendicular to the page and outwards
    3. C 3.14×10−53.14 \times 10^{-5} T, perpendicular to the page and inwards
    4. D 2.6×10−52.6 \times 10^{-5} T, perpendicular to the page and inwards
    Solve this question →

  4. If the magnetic flux density at the centre of a circular loop of radius 4π cm is 5×10−55 \times 10^{-5} T and the magnetic permeability of air is 4π×10−74\pi \times 10^{-7} Wb/A.m, the current in the loop is ..........

    1. A 7 A
    2. B 7.14 A
    3. C 10 A
    4. D 17 A
    Solve this question →

  5. An electric current flows in a circular coil and produces a magnetic field of flux density B at the centre of the coil. When the current is doubled and the diameter of the coil is doubled without changing the number of turns, the flux density at the centre of the coil equals ..........

    1. A B
    2. B 2 B
    3. C B2\dfrac{B}{2}
    4. D B4\dfrac{B}{4}
    Solve this question →

  6. Two metal loops (x) and (y) carry currents I and 2I respectively, and the flux densities at their centres are equal. The ratio between the diameters of the two loops (dxdy)\left(\frac{d_x}{d_y}\right) equals ..........

    1. A 12\dfrac{1}{2}
    2. B 21\dfrac{2}{1}
    3. C 14\dfrac{1}{4}
    4. D 41\dfrac{4}{1}
    Solve this question →

  7. Several circular coils have the same number of turns and carry the same current. Which of the following graphs shows the relation between the magnetic flux density (B) at the centre of each coil and the radius of the coil (r)?

    Figure of question 7
    1. A A
    2. B B
    3. C C
    4. D D
    Solve this question →

  8. The opposite graph shows the relation between the magnetic flux density (B) at the centre of a circular coil of 350 turns and the current (I) in it. The diameter of this circular coil equals ..........

    Figure of question 8
    1. A 10 cm
    2. B 20 cm
    3. C 30 cm
    4. D 40 cm
    Solve this question →

  9. Three groups of metal loops x, y and z carry currents IxI_x, IyI_y and IzI_z respectively. The opposite graph shows the relation between the magnetic flux density (B) at the centre of each loop and the reciprocal of its radius (1r)\left(\frac{1}{r}\right). The correct order of the currents is ..........

    Figure of question 9
    1. A Ix<Iy<IzI_x < I_y < I_z
    2. B Ix>Iy>IzI_x > I_y > I_z
    3. C Ix>Iz>IyI_x > I_z > I_y
    4. D Ix=Iy=IzI_x = I_y = I_z
    Solve this question →

  10. A wire of resistance (R) is shaped into a circular coil with centre (c), and the coil is connected in an electric circuit as in the opposite figure. Closing which of the switches in the circuit increases the magnetic flux density at the centre of the coil due to the current in it?

    Figure of question 10
    1. A Switch (K1)(K_1) only
    2. B Switch (K2)(K_2) only
    3. C Switch (K3)(K_3) only
    4. D All three switches
    Solve this question →

  11. A circular coil of radius 10 cm is made of a wire of cross-sectional area 0.4×10−40.4 \times 10^{-4} m² and resistivity 10−610^{-6} Ω.m. When the coil is connected to a source of emf VBV_B and negligible internal resistance, the flux density at its centre is 0.01 T. The emf of the source equals ..........

    1. A 10 V
    2. B 15 V
    3. C 20 V
    4. D 25 V
    Solve this question →

  12. A potential difference (V) is applied across a circular coil of radius (r), and the magnetic flux density at its centre is (B). When half the turns of the coil are cut off and the ends of the rest of the coil are connected to the same potential difference (V), the magnetic flux density at the centre of the coil ..........

    1. A stays (B)
    2. B becomes (2 B)
    3. C becomes (B4)\left(\dfrac{B}{4}\right)
    4. D becomes (B2)\left(\dfrac{B}{2}\right)
    Solve this question →

  13. A copper wire 50.24 m long with a cross-sectional area of 1.79×10−71.79 \times 10^{-7} m² is wound into a circular coil of radius 4 cm, and its ends are connected to a DC source of emf 12 V and internal resistance 1 Ω. If the resistivity of copper is 1.79×10−81.79 \times 10^{-8} Ω.m, the magnetic flux density at the centre of the coil equals .......... (given: π = 3.14)

    1. A 3.125×10−43.125 \times 10^{-4} T
    2. B 5.93×10−45.93 \times 10^{-4} T
    3. C 6.25×10−36.25 \times 10^{-3} T
    4. D 8.12×10−38.12 \times 10^{-3} T
    Solve this question →

  14. A wire of length (ℓ) is shaped into a circular coil of area (A). When a current (I) flows in the coil, the magnetic flux density (B) at the centre of the coil can be calculated from the relation ..........

    1. A B=μIℓAB = \dfrac{\mu I \ell}{A}
    2. B B=4×μIℓAB = 4 \times \dfrac{\mu I \ell}{A}
    3. C B=12×μIℓAB = \dfrac{1}{2} \times \dfrac{\mu I \ell}{A}
    4. D B=14×μIℓAB = \dfrac{1}{4} \times \dfrac{\mu I \ell}{A}
    Solve this question →

  15. A straight wire 31.4 m long is wound into a circular coil whose face area is 3.14 cm², and a current of 1 A flows in it. The magnetic flux density at the centre of the coil equals .......... (given: π = 3.14)

    1. A 1.57×10−21.57 \times 10^{-2} T
    2. B 3.14×10−23.14 \times 10^{-2} T
    3. C 6.28×10−26.28 \times 10^{-2} T
    4. D 9.42×10−29.42 \times 10^{-2} T
    Solve this question →

  16. A long straight wire carries a current of 5 A, and the magnetic flux density at a point 5 cm (perpendicular distance) from the axis of the wire is B. If a 120 cm piece is cut from this wire and wound into a circular coil of radius 9.55 cm carrying the same current, the magnetic flux density at the centre of the coil ..........

    1. A is greater than (B) by 8.6×10−58.6 \times 10^{-5} T
    2. B is greater than (B) by 4.6×10−54.6 \times 10^{-5} T
    3. C is less than (B) by 8.6×10−58.6 \times 10^{-5} T
    4. D is less than (B) by 4.6×10−54.6 \times 10^{-5} T
    Solve this question →

  17. In the opposite figure, part of a long straight wire is bent into a quarter circle and a current I flows in it. The magnetic flux density at point m equals ..........

    Figure of question 17
    1. A μI2r\dfrac{\mu I}{2r}
    2. B μI4r\dfrac{\mu I}{4r}
    3. C μI6r\dfrac{\mu I}{6r}
    4. D μI8r\dfrac{\mu I}{8r}
    Solve this question →

  18. In the opposite figure, part of a long wire is bent into a semicircle of diameter 40 cm, and a current of 10 A flows in the wire. The magnetic flux density at point X equals ..........

    Figure of question 18
    1. A 3.14×10−53.14 \times 10^{-5} T
    2. B 6.28×10−56.28 \times 10^{-5} T
    3. C 1.57×10−51.57 \times 10^{-5} T
    4. D 2.826×10−42.826 \times 10^{-4} T
    Solve this question →

  19. From the opposite figure:
    The magnetic flux density at point P equals ..........

    Figure of question 19
    1. A 9.43×10−59.43 \times 10^{-5} T
    2. B 6.28×10−56.28 \times 10^{-5} T
    3. C 3.14×10−53.14 \times 10^{-5} T
    4. D 9.43×10−49.43 \times 10^{-4} T
    Solve this question →

  20. From the opposite figure:
    The direction of the magnetic field at point P is ..........

    Figure of question 20
    1. A perpendicular to the page and inwards
    2. B perpendicular to the page and outwards
    3. C in the plane of the page and to the right
    4. D in the plane of the page and to the left
    Solve this question →

  21. The opposite figure shows part of a circular metal loop of radius (r) placed on a horizontal surface and carrying a current I. If the angle θ is measured in degrees, the magnetic flux density at the centre (c) is calculated from the relation ..........

    Figure of question 21
    1. A B=μIθrB = \dfrac{\mu I \theta}{r}
    2. B B=μIθ360 rB = \dfrac{\mu I \theta}{360\, r}
    3. C B=μIθ2πrB = \dfrac{\mu I \theta}{2\pi r}
    4. D B=μIθ720 rB = \dfrac{\mu I \theta}{720\, r}
    Solve this question →

  22. A current flows in a wire 26.4 cm long bent into an arc of a circle of radius 5.6 cm, and the magnetic flux density at the centre of this circle is 8.25×10−68.25 \times 10^{-6} T. The current equals ..........

    1. A 1.5 A
    2. B 0.98 A
    3. C 0.75 A
    4. D 0.49 A
    Solve this question →

  23. The two opposite figures show two half loops made of two wires of the same cross-sectional area, made of a material of high resistivity, with different radii. When the potential difference across each of them was the same, the magnetic flux density at C1C_1 was B. The magnetic flux density at C2C_2 equals ..........

    Figure of question 23
    1. A B2\dfrac{B}{2}
    2. B 2 B
    3. C 3 B
    4. D 4 B
    Solve this question →

  24. Which of the following coils has the greatest flux density at its centre?

    Figure of question 24
    1. A A
    2. B B
    3. C C
    4. D D
    Solve this question →

  25. The opposite figure shows a circular coil of 14 turns and radius 8 cm in the plane of the page, carrying a current of 12 A. A uniform external magnetic field of flux density 10−510^{-5} T acts on it, perpendicular to the page and inwards. The magnitude and direction of the resultant flux density at the centre of the coil (P) are ..........

    Figure of question 25
    1. A magnitude 1.33×10−31.33 \times 10^{-3} T, perpendicular to the page and inwards
    2. B magnitude 1.33×10−31.33 \times 10^{-3} T, perpendicular to the page and outwards
    3. C magnitude 3.13×10−33.13 \times 10^{-3} T, perpendicular to the page and inwards
    4. D magnitude 3.13×10−33.13 \times 10^{-3} T, perpendicular to the page and outwards
    Solve this question →

  26. In the opposite figure, a circular coil carrying a current is placed parallel to a uniform magnetic field of flux density B, and the resultant flux density at the centre of the coil is 5\sqrt{5} B. When the coil is rotated through 90°, the resultant flux density at the centre of the coil can be ..........

    Figure of question 26
    1. A B or 2 B
    2. B B or 5 B
    3. C B or 3 B
    4. D zero or B
    Solve this question →

  27. The opposite figure shows a straight wire, part of which is shaped into a quarter of a circular turn in the plane of the page. An external magnetic field of flux density 6×10−66 \times 10^{-6} T acts on it, perpendicular to the page and outwards. The resultant magnetic flux density at its centre P equals ..........

    Figure of question 27
    1. A 11×10−511 \times 10^{-5} T
    2. B 5.6×10−55.6 \times 10^{-5} T
    3. C 4.4×10−54.4 \times 10^{-5} T
    4. D 0
    Solve this question →

  28. A circular loop of radius 5 cm carries a current of 10 A. If the loop is bent at its middle so that each half is perpendicular to the other half, the resultant magnetic flux density at the centre equals ..........

    1. A 8.9×10−58.9 \times 10^{-5} T
    2. B 7.3×10−57.3 \times 10^{-5} T
    3. C 13.21×10−613.21 \times 10^{-6} T
    4. D 12.5×10−612.5 \times 10^{-6} T
    Solve this question →

  29. A straight wire of resistance 48 Ω is shaped into a closed loop of diameter 0.1 m, and a 6 V battery of negligible internal resistance is connected across the ends of its diameter as in the figure. Then:
    The current in either half of the loop equals ..........

    Figure of question 29
    1. A 0.75 A
    2. B 0.25 A
    3. C 0.36 A
    4. D 0.41 A
    Solve this question →

  30. A straight wire of resistance 48 Ω is shaped into a closed loop of diameter 0.1 m, and a 6 V battery of negligible internal resistance is connected across the ends of its diameter as in the figure. Then:
    The magnetic flux density at the centre of the loop equals ..........

    Figure of question 30
    1. A 0
    2. B π μT
    3. C 2π μT
    4. D 3π μT
    Solve this question →

  31. A metal loop with centre x is connected to a voltage source through two points (a, b) on the circumference of the loop as in the opposite figure, so a current flows through it. The resultant magnetic flux density at the centre of the loop equals ..........

    Figure of question 31
    1. A 3μ8r\dfrac{3\mu}{8r}
    2. B 6μ8r\dfrac{6\mu}{8r}
    3. C 4μ8r\dfrac{4\mu}{8r}
    4. D 0
    Solve this question →

  32. Two wires x and y are made of the same metal; the cross-sectional area of wire (x) is twice that of wire (y). They are joined together to form one circular loop, and a current flows in it as in the opposite figure. The magnetic flux density at the centre (c) equals ..........

    Figure of question 32
    1. A 1.26×10−51.26 \times 10^{-5} T
    2. B 7.54×10−67.54 \times 10^{-6} T
    3. C 4.71×10−64.71 \times 10^{-6} T
    4. D 3.77×10−63.77 \times 10^{-6} T
    Solve this question →

  33. A metal loop carries an electric current through several paths as shown in the opposite figure. The direction of the magnetic flux density at the centre of the loop is ..........

    Figure of question 33
    1. A inwards, perpendicular to the plane of the loop
    2. B outwards, perpendicular to the plane of the loop
    3. C to the right, towards point m
    4. D to the left, towards point k
    Solve this question →

  34. A current I flows in a straight wire wound into a circle of one turn. Then the same wire is wound into a circular coil of four turns and a current I2\frac{I}{2} flows in it. The ratio of the flux density at the centre of the coil in the first case to that in the second case equals ..........

    1. A 49\dfrac{4}{9}
    2. B 94\dfrac{9}{4}
    3. C 18\dfrac{1}{8}
    4. D 81\dfrac{8}{1}
    Solve this question →

  35. According to Bohr's model of the hydrogen atom, the electron revolves around the nucleus in a circular orbit of radius 5.3×10−115.3 \times 10^{-11} m with a frequency of 6.6×10156.6 \times 10^{15} Hz. The magnetic flux density at the centre of the orbit due to the electron's motion equals ..........

    1. A 12.52 T
    2. B 8.48 T
    3. C 5.65 T
    4. D 4.24 T
    Solve this question →

  36. Two concentric metal loops in the same plane each carry a current I as in the figure. The direction of the magnetic flux at the common centre m is towards ..........

    Figure of question 36
    1. A the right of the page
    2. B the left of the page
    3. C into the page
    4. D out of the page
    Solve this question →

  37. Two concentric loops in the plane of the page carry equal currents (I) in opposite directions as in the opposite figure. Which of the following actions reverses the direction of the resultant magnetic flux density at the centre of the two loops (c)?

    Figure of question 37
    1. A Decreasing the current of the inner loop to 23\dfrac{2}{3} I
    2. B Decreasing the current of the inner loop to 12\dfrac{1}{2} I
    3. C Increasing the current of the outer loop to 2 I
    4. D Increasing the current of the outer loop to 3 I
    Solve this question →

  38. Two concentric circular coils in the same plane have 400 turns and 500 turns and radii 20 cm and 10 cm respectively. They carry currents in the same direction of 7 A and 10 A respectively. Then:
    The magnetic flux density at the common centre of the two coils equals ..........

    1. A 16.3×10−316.3 \times 10^{-3} T
    2. B 32.6×10−332.6 \times 10^{-3} T
    3. C 40.2×10−340.2 \times 10^{-3} T
    4. D 81.5×10−381.5 \times 10^{-3} T
    Solve this question →

  39. Two concentric circular coils in the same plane have 400 turns and 500 turns and radii 20 cm and 10 cm respectively. They carry currents in the same direction of 7 A and 10 A respectively. Then:
    The magnetic flux density at the common centre when one coil is rotated through 180° about the common centre, so that it is turned over, equals ..........

    1. A 22.6×10−322.6 \times 10^{-3} T
    2. B 45.3×10−345.3 \times 10^{-3} T
    3. C 67.8×10−367.8 \times 10^{-3} T
    4. D 90.4×10−390.4 \times 10^{-3} T
    Solve this question →

  40. Two concentric circular coils in the same plane have 400 turns and 500 turns and radii 20 cm and 10 cm respectively. They carry currents in the same direction of 7 A and 10 A respectively. Then:
    The magnetic flux density at the common centre when one coil is rotated through 90° about the common centre, so that the two coils become perpendicular, equals ..........

    1. A 18.5×10−318.5 \times 10^{-3} T
    2. B 32.6×10−332.6 \times 10^{-3} T
    3. C 65.2×10−365.2 \times 10^{-3} T
    4. D 97.8×10−397.8 \times 10^{-3} T
    Solve this question →

  41. Two concentric circular coils in the same plane carry equal currents in opposite directions. The first has a diameter of 10 cm and 100 turns, and the second has a diameter of 20 cm. The number of turns of the second coil that makes the flux density at their common centre zero equals ..........

    1. A 50 turns
    2. B 100 turns
    3. C 150 turns
    4. D 200 turns
    Solve this question →

  42. In the figure shown, if a current of 1 A flows in the wires, the resultant flux density at point c is ..........

    Figure of question 42
    1. A μ5r\dfrac{\mu}{5r}
    2. B μ2r\dfrac{\mu}{2r}
    3. C μ4r\dfrac{\mu}{4r}
    4. D μ8r\dfrac{\mu}{8r}
    Solve this question →

  43. A circular loop and part of another circular loop are concentric with radii r and 2r respectively and lie in the same plane. They carry currents I and 9I respectively as in the opposite figure, and the resultant magnetic flux density at the centre (c) is zero. The angle θ equals ..........

    Figure of question 43
    1. A 60°
    2. B 80°
    3. C 90°
    4. D 95°
    Solve this question →

  44. Two concentric circular coils in the same plane: the diameter of the first is twice that of the second. They carry the same current in the same direction, and B1B_1 (outer coil) > B2B_2 (inner coil). When the current in the outer coil is reversed, the flux density due to both at the centre drops to half. The ratio of the numbers of turns of the two coils N1N2\frac{N_1}{N_2} equals ..........

    1. A 45\dfrac{4}{5}
    2. B 611\dfrac{6}{11}
    3. C 23\dfrac{2}{3}
    4. D 98\dfrac{9}{8}
    Solve this question →

  45. In each of the following figures, three concentric metal loops in the same plane carry currents of the same magnitude. In which figure is the magnetic flux density at the centre the smallest?

    Figure of question 45
    1. A A
    2. B B
    3. C C
    4. D D
    Solve this question →

  46. Three concentric loops (x), (y) and (z) with centre (c) lie in the same plane, and each carries a current as shown in the opposite figure. If the resultant magnetic flux density at the centre (c) is zero, the magnitude and direction of the current in loop (y) are ..........

    Figure of question 46
    1. A 1.5 I, clockwise
    2. B 1.5 I, anticlockwise
    3. C 2.7 I, clockwise
    4. D 2.7 I, anticlockwise
    Solve this question →

  47. Four circular metal half loops are connected together and to a battery as in the opposite figure. The direction of the resultant magnetic flux density at the common centre (c) is ..........

    Figure of question 47
    1. A perpendicular to the page and outwards
    2. B perpendicular to the page and inwards
    3. C in the plane of the page and to the right
    4. D in the plane of the page and to the left
    Solve this question →

  48. A long straight wire carries a current (I), and the magnetic flux density at a point at a perpendicular distance (d) from it is (B). If a current of the same magnitude (I) flows in a circular loop and the flux density at its centre is also (B), the radius of the loop is ..........

    1. A greater than (d)
    2. B less than (d)
    3. C equal to (d)
    4. D the answer cannot be determined
    Solve this question →

  49. The opposite figure shows part of a metal loop with centre X. A long straight wire in the same plane is 20 cm from the centre of the loop and carries a current I. The magnitude and direction of the current I needed to make the magnetic flux density at the centre of the loop zero are ..........

    Figure of question 49
    1. A 15 A, from a to b
    2. B 30 A, from a to b
    3. C 15 A, from b to a
    4. D 30 A, from b to a
    Solve this question →

  50. A straight wire is placed vertically so that it touches a circular coil of one turn whose plane is in the plane of the magnetic meridian. A magnetic needle, free to move in a horizontal plane, is placed at the centre of the coil. The current in the wire that causes no deflection of the needle when the coil carries a current of 0.42 A equals ..........

    1. A 0.96 A
    2. B 1.07 A
    3. C 1.32 A
    4. D 2.56 A
    Solve this question →

  51. In the opposite figure, a long straight wire touches a circular coil, lies in the same plane and is insulated from it, and each carries a current in the direction shown. If the resultant magnetic flux density at the centre of the coil is zero, and then the coil is turned over, the resultant magnetic flux density at the centre of the coil becomes ..........

    Figure of question 51
    1. A half the flux density of the coil
    2. B the flux density of the coil
    3. C the flux density of the wire
    4. D twice the flux density of the wire
    Solve this question →

  52. An insulated straight wire carrying a current I is placed touching a semicircular loop, either in the same plane or perpendicular to it. The loop carries a current I in the direction shown in the following figures.
    The correct order of the magnetic flux densities at the centre of the half loop in these cases is ..........

    Figure of question 52
    1. A B4>B2>B3>B1B_4 > B_2 > B_3 > B_1
    2. B B1>B3=B4>B2B_1 > B_3 = B_4 > B_2
    3. C B2>B3=B4>B1B_2 > B_3 = B_4 > B_1
    4. D B3=B4>B2>B1B_3 = B_4 > B_2 > B_1
    Solve this question →

  53. In the figure shown, a long straight wire is placed near a metal loop, perpendicular to its plane, and each carries a current of 10 A. The magnitude of the resultant magnetic flux density at the centre of the loop (c) is approximately ..........

    Figure of question 53
    1. A 10−410^{-4} T
    2. B 2.6×10−42.6 \times 10^{-4} T
    3. C 3.2×10−43.2 \times 10^{-4} T
    4. D 3.6×10−43.6 \times 10^{-4} T
    Solve this question →

  54. An insulated long wire carrying a current I has a part wound into a circular loop of radius r in two ways, as in the following two figures.
    The ratio between the resultant magnetic flux densities at the centre of the loop in the two figures (B1B2)\left(\frac{B_1}{B_2}\right) is ..........

    Figure of question 54
    1. A 11\dfrac{1}{1}
    2. B π+1π\dfrac{\pi + 1}{\pi}
    3. C 1π−1\dfrac{1}{\pi - 1}
    4. D π+1π−1\dfrac{\pi + 1}{\pi - 1}
    Solve this question →

  55. A circular loop of radius 2.5 cm carries a current of 3 A. A long straight wire in the same plane, 5 cm from the loop, carries a current I as in the figure. Then:
    The value of I that makes the flux density at the centre of the loop zero is ..........

    Figure of question 55
    1. A 35.64 A
    2. B 28.29 A
    3. C 23.79 A
    4. D 20.81 A
    Solve this question →

  56. A circular loop of radius 2.5 cm carries a current of 3 A. A long straight wire in the same plane, 5 cm from the loop, carries a current I as in the figure. Then:
    The flux density at the centre of the loop if the direction of the current I is reversed equals ..........

    Figure of question 56
    1. A 7.54×10−37.54 \times 10^{-3} T
    2. B 3.79×10−33.79 \times 10^{-3} T
    3. C 1.51×10−41.51 \times 10^{-4} T
    4. D 2.24×10−42.24 \times 10^{-4} T
    Solve this question →

  57. In the opposite figure, a circular loop and a straight wire placed at position x in the same plane as the loop each carry a current I, and the resultant flux density at the centre of the loop c is B. If the wire is moved to position y, the flux density at point c becomes ..........

    Figure of question 57
    1. A 2 B
    2. B B
    3. C 0.73 B
    4. D 1.38 B
    Solve this question →

  58. Two concentric circular loops in the same plane have radii r and 2r, and each carries a current I in opposite directions. A long straight wire is placed touching the outer loop, in the same plane, and carries a current IoI_o as in the opposite figure. If the resultant magnetic flux density at the centre of the two loops (C) is zero, the ratio of the two currents (IoI)\left(\frac{I_o}{I}\right) equals ..........

    Figure of question 58
    1. A π
    2. B 1π\dfrac{1}{\pi}
    3. C 2π
    4. D 12π\dfrac{1}{2\pi}
    Solve this question →

  59. Two parallel straight wires A and B, 1 m apart, carry currents in the same direction of 4.5 A and 1.5 A respectively. A circular coil of one turn and radius 10π cm is placed in the same plane as the two wires, with its centre 0.5 m from wire A as shown in the figure. The magnitude and direction of the current in the circular coil that makes the magnetic flux density at its centre zero are ..........

    Figure of question 59
    1. A 0.3 A, clockwise
    2. B 0.6 A, clockwise
    3. C 0.3 A, anticlockwise
    4. D 0.6 A, anticlockwise
    Solve this question →

  60. Using the opposite figure, if the magnetic flux density due to the current in each of the two straight wires at the centre of the circular coil (m) is B, and the resultant magnetic flux density at the centre of the coil (m) is zero, then ..........

    Figure of question 60
    1. A current in the coil: clockwise, flux density of the coil: B2\dfrac{B}{2}
    2. B current in the coil: anticlockwise, flux density of the coil: B2\dfrac{B}{2}
    3. C current in the coil: clockwise, flux density of the coil: 2 B
    4. D current in the coil: anticlockwise, flux density of the coil: 2 B
    Solve this question →

  61. A metal loop carrying a current I moves between two straight wires, each carrying a current I, placed in the same plane as the loop as in the opposite figure. What is the correct order of the resultant magnetic flux density at the centre of the loop (c) when it is fixed at each of the three positions shown in the figure?

    Figure of question 61
    1. A Bz>By>BxB_z > B_y > B_x
    2. B Bx>By>BzB_x > B_y > B_z
    3. C Bx>Bz>ByB_x > B_z > B_y
    4. D Bx=By=BzB_x = B_y = B_z
    Solve this question →

  62. A metal loop of radius (r) carries a current (I), and a long straight wire in the same plane, at a distance 2r from its centre, carries a current (I) as in figure (1). If the wire is bent and carries the same current as in figure (2), what happens to the magnitude and direction of the resultant magnetic flux density at the centre of the loop?

    Figure of question 62
    1. A Its magnitude increases and its direction stays the same
    2. B Its magnitude increases and its direction reverses
    3. C Its magnitude decreases and its direction stays the same
    4. D Its magnitude decreases and its direction reverses
    Solve this question →

  63. The magnetic field produced by a current in a solenoid has the advantage over the magnetic field of a bar magnet that we can control ..........

    1. A the magnetic polarity only
    2. B the magnetic flux density only
    3. C the direction of the magnetic field only
    4. D the polarity, flux density and direction of the magnetic field
    Solve this question →

  64. From the opposite figure, which of the following doubles the magnetic flux density inside the solenoid, other factors being constant?

    Figure of question 64
    1. A Doubling the length of the coil (ℓ)
    2. B Doubling the emf (VB)(V_B)
    3. C Halving the number of turns of the coil (N)
    4. D Doubling the electric resistance (R)
    Solve this question →

  65. The following figures show a permanent magnet hanging freely near a solenoid carrying an electric current.
    In which two of these figures is the magnet attracted to the coil?

    Figure of question 65
    1. A (1), (2)
    2. B (3), (4)
    3. C (1), (3)
    4. D (2), (3)
    Solve this question →

  66. Two identical solenoids (1) and (2) are each connected to a battery of emf (VB)(V_B) with negligible internal resistance and a switch. A ring magnet hangs between the two coils at equal distances from them, as in the following figure.
    After closing the two switches K1K_1 and K2K_2 together, the magnet ..........

    Figure of question 66
    1. A is attracted to coil (1)
    2. B is attracted to coil (2)
    3. C rotates about its axis
    4. D stays still
    Solve this question →

  67. Two compasses (1) and (2) are placed on either side of a solenoid connected to a battery and a switch (K), and the compass needles settle under the Earth's magnetic field as shown in the opposite figure. Which of the following figures shows the position in which the two needles settle when the switch K is closed?

    Figure of question 67
    1. A A
    2. B B
    3. C C
    4. D D
    Solve this question →

  68. A solenoid 20 cm long with 200 turns carries a current of 0.5 A. The flux density at the middle of its length on its axis (given: the magnetic permeability of iron = 2×10−32 \times 10^{-3} Wb/A.m, π = 3.14):
    if the medium is air, equals ..........

    1. A 8.93×10−58.93 \times 10^{-5} T
    2. B 3.11×10−43.11 \times 10^{-4} T
    3. C 6.28×10−46.28 \times 10^{-4} T
    4. D 7.92×10−57.92 \times 10^{-5} T
    Solve this question →

  69. A solenoid 20 cm long with 200 turns carries a current of 0.5 A. The flux density at the middle of its length on its axis (given: the magnetic permeability of iron = 2×10−32 \times 10^{-3} Wb/A.m, π = 3.14):
    if an iron core is placed inside the coil, equals ..........

    1. A 0.5 T
    2. B 0.25 T
    3. C 0.75 T
    4. D 1 T
    Solve this question →

  70. A solenoid 0.22 m long with a face area of 25×10−425 \times 10^{-4} m² has 300 turns and carries a current, and the flux density at a point at the middle of its length on its axis is 1.2×10−31.2 \times 10^{-3} Wb/m². Then:
    The current in the coil equals ..........

    1. A 0.3 A
    2. B 0.5 A
    3. C 0.7 A
    4. D 1.1 A
    Solve this question →

  71. A solenoid 0.22 m long with a face area of 25×10−425 \times 10^{-4} m² has 300 turns and carries a current, and the flux density at a point at the middle of its length on its axis is 1.2×10−31.2 \times 10^{-3} Wb/m². Then:
    The total flux passing through a cross-section at the middle of the coil equals ..........

    1. A 3×10−63 \times 10^{-6} Wb
    2. B 5×10−65 \times 10^{-6} Wb
    3. C 9×10−69 \times 10^{-6} Wb
    4. D 18×10−618 \times 10^{-6} Wb
    Solve this question →

  72. A solenoid 0.6 m long carries a current of 10 A, and the flux density at a point at the middle of its length on its axis is 0.05 T. Then:
    The number of turns per unit length equals .......... turns/m.

    1. A 2388.5
    2. B 3679.4
    3. C 3977.3
    4. D 5123.5
    Solve this question →

  73. A solenoid 0.6 m long carries a current of 10 A, and the flux density at a point at the middle of its length on its axis is 0.05 T. Then:
    Its number of turns equals .......... turns.

    1. A 1194.5
    2. B 2386.4
    3. C 3582.7
    4. D 8359.3
    Solve this question →

  74. A solenoid of N turns and length 50 cm, with a resistance of 0.01 Ω per turn, is connected to a 2 V source of negligible internal resistance. Then:
    The magnetic flux density at a point at the middle of its length on its axis equals ..........

    1. A 2.15×10−32.15 \times 10^{-3} T
    2. B 4.11×10−34.11 \times 10^{-3} T
    3. C 3.17×10−43.17 \times 10^{-4} T
    4. D 5.03×10−45.03 \times 10^{-4} T
    Solve this question →

  75. A solenoid of N turns and length 50 cm, with a resistance of 0.01 Ω per turn, is connected to a 2 V source of negligible internal resistance. Then:
    The value the magnetic flux density will have if half of its turns are cut off and the other half is connected to the same source is ..........

    1. A 1.01×10−31.01 \times 10^{-3} T
    2. B 3.09×10−33.09 \times 10^{-3} T
    3. C 2.17×10−42.17 \times 10^{-4} T
    4. D 7.18×10−47.18 \times 10^{-4} T
    Solve this question →

  76. A solenoid 20 cm long with 100 turns and a resistance of 6 Ω is part of the electric circuit shown. The magnetic flux density at a point at the middle of its length on its axis, due to the current in it, when:
    switch K is open, equals ..........

    Figure of question 76
    1. A 3.14×10−33.14 \times 10^{-3} T
    2. B 4.71×10−34.71 \times 10^{-3} T
    3. C 6.22×10−36.22 \times 10^{-3} T
    4. D 9.78×10−39.78 \times 10^{-3} T
    Solve this question →

  77. A solenoid 20 cm long with 100 turns and a resistance of 6 Ω is part of the electric circuit shown. The magnetic flux density at a point at the middle of its length on its axis, due to the current in it, when:
    switch K is closed, equals ..........

    Figure of question 77
    1. A 3.14×10−33.14 \times 10^{-3} T
    2. B 5.19×10−35.19 \times 10^{-3} T
    3. C 6.03×10−36.03 \times 10^{-3} T
    4. D 7.16×10−37.16 \times 10^{-3} T
    Solve this question →

  78. The opposite figure shows a solenoid of negligible resistance in an electric circuit. Which of the following graphs shows the relation between the magnetic flux density (B) at a point at the middle of the coil on its axis and the resistance taken from the rheostat (Rs)(R_s)?

    Figure of question 78
    1. A A
    2. B B
    3. C C
    4. D D
    Solve this question →

  79. In the opposite electric circuit, what happens to the magnetic flux density inside the solenoid, due to the current in the coil, when the value of:
    resistance R1R_1 is increased?

    Figure of question 79
    1. A It increases
    2. B It decreases
    3. C It does not change
    4. D The answer cannot be determined
    Solve this question →

  80. In the opposite electric circuit, what happens to the magnetic flux density inside the solenoid, due to the current in the coil, when the value of:
    resistance R2R_2 is increased?

    Figure of question 80
    1. A It increases
    2. B It decreases
    3. C It does not change
    4. D The answer cannot be determined
    Solve this question →

  81. The opposite graph shows the relation between the magnetic flux density (B) at a point at the middle of a solenoid on its axis and the current (I) in it. The number of turns per metre of the coil equals ..........

    Figure of question 81
    1. A 215.2 turns/m
    2. B 250.5 turns/m
    3. C 318.18 turns/m
    4. D 341.4 turns/m
    Solve this question →

  82. Two solenoids (x) and (y) have the same number of turns and cores of two different materials; the length of coil (y) is four times the length of coil (x), and each carries a current. The opposite graph shows the relation between the magnetic flux density (B) at the middle of each coil on its axis and the current (I) in each. Which core is made of the material with the greater magnetic permeability?

    Figure of question 82
    1. A The core of coil (x)
    2. B The core of coil (y)
    3. C The permeabilities of the two core materials are equal
    4. D The answer cannot be determined
    Solve this question →

  83. In the opposite figure, a solenoid 10π cm long with 500 turns is connected in series with a battery and a resistor R. If the magnetic flux density at a point at the middle of the coil on its axis is 2.4×10−22.4 \times 10^{-2} T and its end D is a south pole, the magnitude and direction of the current in resistor R are ..........

    Figure of question 83
    1. A 12 A, from a to b
    2. B 12 A, from b to a
    3. C 24 A, from a to b
    4. D 24 A, from b to a
    Solve this question →

  84. In the opposite figure, a wire is wound as a long solenoid and connected to a battery. The magnetic poles formed at the ends A and B respectively are ..........

    Figure of question 84
    1. A north, north
    2. B north, south
    3. C south, north
    4. D south, south
    Solve this question →

  85. In the opposite figure, a coil is fixed above a piece of soft iron placed on the pan of a balance that reads w. What happens to the balance reading when one of the switches K1K_1 or K2K_2 is closed while the other is kept open?

    Figure of question 85
    1. A It increases above w in both cases
    2. B It decreases below w in both cases
    3. C It increases above w in one case and decreases below w in the other
    4. D It stays w in both cases
    Solve this question →

  86. In the opposite figure, a solenoid of resistance (R) is connected to two identical batteries through two switches K1K_1 and K2K_2, and a magnet hangs freely from a thread above the coil. Which of the following decreases the tension in the thread?

    Figure of question 86
    1. A Closing switch (K1)(K_1) only
    2. B Closing switch (K2)(K_2) only
    3. C Closing switches (K1)(K_1) and (K2)(K_2) together
    4. D The answer cannot be determined
    Solve this question →

  87. An insulated wire of diameter 0.2 cm is wound around an iron rod of magnetic permeability 2×10−32 \times 10^{-3} Wb/A.m so that the turns touch each other along the rod. If a current of 1 A flows in it, the magnetic flux density at a point at the middle of its length on its axis equals ..........

    1. A 0.5 T
    2. B 1 T
    3. C 1.2 T
    4. D 1.5 T
    Solve this question →

  88. A uniformly wound solenoid has length ℓ and N turns. If the coil is cut into two parts x and y of lengths ℓ1\ell_1 and 3ℓ13\ell_1 respectively, and each is connected to the same potential difference, the ratio of the magnetic flux densities (BxBy)\left(\frac{B_x}{B_y}\right) at the middle of each part on its axis equals ..........

    1. A 11\dfrac{1}{1}
    2. B 13\dfrac{1}{3}
    3. C 14\dfrac{1}{4}
    4. D 31\dfrac{3}{1}
    Solve this question →

  89. Two identical solenoids, the first of copper and the second of aluminium, are each connected separately to the same battery, and the magnetic flux densities at the middle of their axes due to the current in them are B1B_1 and B2B_2 respectively. Then .......... (given: the resistivity of copper is less than that of aluminium)

    1. A B1>B2B_1 > B_2
    2. B B1<B2B_1 < B_2
    3. C B1=B2=0B_1 = B_2 = 0
    4. D B1=B2≠0B_1 = B_2 \neq 0
    Solve this question →

  90. The opposite figure shows two solenoids x and y with the same number of turns wound around an iron cylinder, each carrying a direct current. The ratio of the magnetic flux densities at the middle of each coil on its axis (BxBy)\left(\frac{B_x}{B_y}\right) equals ..........

    Figure of question 90
    1. A 21\dfrac{2}{1}
    2. B 14\dfrac{1}{4}
    3. C 11\dfrac{1}{1}
    4. D 12\dfrac{1}{2}
    Solve this question →

  91. Two solenoids X and Y have the same number of turns per unit length and are made of two copper wires of the same length but different cross-sectional areas, connected to two sources of the same voltage. If the ratio of the magnetic flux densities at the middle of each coil on its axis is BXBY=91\frac{B_X}{B_Y} = \frac{9}{1}, which of the following is correct?

    1. A The cross-sectional area of the wire of coil X is three times that of coil Y
    2. B The cross-sectional area of the wire of coil X is nine times that of coil Y
    3. C The resistance of coil X is three times that of coil Y
    4. D The resistance of coil X is twice that of coil Y
    Solve this question →

  92. The opposite figure shows a solenoid of 60 turns carrying a current. If the whole coil is placed in an external magnetic field of flux density 5.2×10−35.2 \times 10^{-3} T, parallel to the axis of the coil and to the right of the page, then at the middle of the solenoid on its axis the resultant magnetic flux density and its direction are ..........

    Figure of question 92
    1. A 2.8×10−32.8 \times 10^{-3} T, in the direction of the external field
    2. B 2.8×10−32.8 \times 10^{-3} T, opposite to the external field
    3. C 7.6×10−37.6 \times 10^{-3} T, opposite to the external field
    4. D 7.6×10−37.6 \times 10^{-3} T, in the direction of the external field
    Solve this question →

  93. In the opposite electric circuit, the solenoid has 210 turns and a length of 1.1 m and is placed in an external magnetic field parallel to the axis of the coil with a flux density of 1.2×10−31.2 \times 10^{-3} T. The current that must flow in the circuit to make the resultant magnetic flux density at the middle of the solenoid on its axis zero, and the type of the battery terminals, are ..........

    Figure of question 93
    1. A current 8 A, battery terminals: a positive, b negative
    2. B current 8 A, battery terminals: a negative, b positive
    3. C current 5 A, battery terminals: a positive, b negative
    4. D current 5 A, battery terminals: a negative, b positive
    Solve this question →

  94. In the figure shown, two identical solenoids with parallel axes each carry a current. The direction of their total magnetic field at point x is ..........

    Figure of question 94
    1. A into the page
    2. B out of the page
    3. C towards the top of the page
    4. D towards the bottom of the page
    Solve this question →

  95. A student designed an apparatus to study the magnetic field produced by a current in two identical solenoids x and y, as in the opposite figure. What do you expect to happen when switch (K) is closed?

    Figure of question 95
    1. A The two coils repel
    2. B The two coils attract
    3. C No magnetic force is produced between the two coils
    4. D The two coils vibrate vertically
    Solve this question →

  96. Two solenoids, one inside the other, have a common axis. Each unit length of the first coil has 10 turns and of the second 20 turns. If the current in the first coil is 2 A and in the second 4 A, the magnetic flux density at the middle of their lengths on the axis:
    when the two currents are in the same direction, equals ..........

    1. A 125.71×10−6125.71 \times 10^{-6} T
    2. B 432.7×10−5432.7 \times 10^{-5} T
    3. C 79.7×10−479.7 \times 10^{-4} T
    4. D 45.31×10−345.31 \times 10^{-3} T
    Solve this question →

  97. Two solenoids, one inside the other, have a common axis. Each unit length of the first coil has 10 turns and of the second 20 turns. If the current in the first coil is 2 A and in the second 4 A, the magnetic flux density at the middle of their lengths on the axis:
    when the two currents are in opposite directions, equals ..........

    1. A 96.41×10−696.41 \times 10^{-6} T
    2. B 85.7×10−685.7 \times 10^{-6} T
    3. C 75.43×10−675.43 \times 10^{-6} T
    4. D 41.8×10−641.8 \times 10^{-6} T
    Solve this question →

  98. In the figure shown, there are two identical solenoids. The resultant magnetic flux density at the middle of the two coils on their common axis (point p) after closing switch K ..........

    Figure of question 98
    1. A increases
    2. B decreases
    3. C does not change
    4. D becomes zero
    Solve this question →

  99. A circular coil of N turns and radius r carries a current I, and the flux density at its centre is B. If its turns are spread out uniformly to form a solenoid of length 20r carrying the same current, the flux density at a point at the middle of its length on its axis is ..........

    1. A B20\dfrac{B}{20}
    2. B B10\dfrac{B}{10}
    3. C B40\dfrac{B}{40}
    4. D B
    Solve this question →

  100. A circular coil of radius 2.2 cm carries a current and produces a magnetic field of flux density B. If its turns are spread apart uniformly until its length becomes 110 cm, the flux density at a point at the middle of its length on its axis equals ..........

    1. A B
    2. B 2 B
    3. C 0.5 B
    4. D 0.04 B
    Solve this question →

  101. A solenoid of diameter 10 cm and length 200 cm carries a current that produces a magnetic flux density of 4×10−64 \times 10^{-6} T at the middle of its length on its axis. If its turns are pressed together uniformly until it becomes a circular coil, the flux density at the centre of the coil in this case equals ..........

    1. A 2.75×10−32.75 \times 10^{-3} T
    2. B 4.5×10−34.5 \times 10^{-3} T
    3. C 8×10−58 \times 10^{-5} T
    4. D 13×10−313 \times 10^{-3} T
    Solve this question →

  102. A solenoid 50 cm long with 100 turns carries a current of 2 A. A circular coil is placed exactly at its middle so that the centre of the circular coil is on the axis of the solenoid and its plane is perpendicular to that axis. If the circular coil has 20 turns, carries a current of 1 A and has a radius of 15 cm, the flux density at the centre of the circular coil if the two currents are:
    in the same direction, equals ..........

    1. A 3.32×10−43.32 \times 10^{-4} T
    2. B 4.19×10−44.19 \times 10^{-4} T
    3. C 5.87×10−45.87 \times 10^{-4} T
    4. D 6.93×10−46.93 \times 10^{-4} T
    Solve this question →

  103. A solenoid 50 cm long with 100 turns carries a current of 2 A. A circular coil is placed exactly at its middle so that the centre of the circular coil is on the axis of the solenoid and its plane is perpendicular to that axis. If the circular coil has 20 turns, carries a current of 1 A and has a radius of 15 cm, the flux density at the centre of the circular coil if the two currents are:
    in opposite directions, equals ..........

    1. A 4.19×10−44.19 \times 10^{-4} T
    2. B 9.73×10−39.73 \times 10^{-3} T
    3. C 8.62×10−48.62 \times 10^{-4} T
    4. D 12.5×10−412.5 \times 10^{-4} T
    Solve this question →

  104. In which of the following figures is the resultant magnetic flux density at the middle of the solenoid (point c) in the plane of the page and to the left?

    Figure of question 104
    1. A A
    2. B B
    3. C C
    4. D D
    Solve this question →

  105. In the figure shown, a solenoid carries a current that produces a flux density B at a point at the middle of its length on its axis (point p). Next to it, a straight wire perpendicular to the plane of the page carries a current that produces a flux density B at point p. The total flux density at point p is ..........

    Figure of question 105
    1. A zero
    2. B B
    3. C 2\sqrt{2} B
    4. D 2 B
    Solve this question →

  106. A straight wire carrying a current of 15 A is placed perpendicular to the axis of a solenoid of 10 turns and length 15 cm that carries a current of 722\frac{7}{22} A, as in the figure. The magnetic flux density at point y, at the middle of the coil on its axis and 15 cm from the wire, equals ..........

    Figure of question 106
    1. A 11.5×10−311.5 \times 10^{-3} T
    2. B 3.34×10−53.34 \times 10^{-5} T
    3. C 5.67×10−45.67 \times 10^{-4} T
    4. D 9.7×10−69.7 \times 10^{-6} T
    Solve this question →

  107. A straight wire (y), perpendicular to the plane of the page, is 2 cm from the axis of a solenoid of 50 turns/m carrying a current of 1.4 A, as in the figure. For the resultant magnetic flux density at a point at the middle of the solenoid on its axis (point z) to be zero, the magnitude and direction of the current in the wire are ..........

    Figure of question 107
    1. A 2.2 A, perpendicular to the page and inwards
    2. B 6.6 A, perpendicular to the page and inwards
    3. C 8.8 A, perpendicular to the page and outwards
    4. D 4.4 A, perpendicular to the page and outwards
    Solve this question →

  108. In the figure shown, a solenoid carries a current that produces a flux density of 3×10−63 \times 10^{-6} T at the middle of the coil on its axis (point X). A straight wire in the plane of the page next to it carries a current that produces a flux density of 4×10−64 \times 10^{-6} T at point X. The total flux density at point X equals ..........

    Figure of question 108
    1. A 10−610^{-6} T
    2. B 5×10−65 \times 10^{-6} T
    3. C 7×10−67 \times 10^{-6} T
    4. D 12×10−612 \times 10^{-6} T
    Solve this question →

Solve the multiple choice questions online with explained answers →

Essay questions

  1. Several wires are shaped as in the following figures and each carries an electric current. Arrange in ascending order the magnetic flux density B at the centre (c) in each figure.

    Figure of question 1Solve this question →

  2. Two straight wires x and y are made of the same material and have equal lengths; the cross-sectional area of wire x is half that of wire y. The two wires are shaped into half loops (1) and (2) respectively, and the potential difference across each is V as in the opposite figure. Calculate the ratio of the magnetic flux densities BxBy\frac{B_x}{B_y} at the centres C1C_1 and C2C_2.

    Figure of question 2Solve this question →

  3. An electric current flows in a circular coil of N1N_1 turns and produces a magnetic flux of density B1B_1 at its centre. If the coil is rewound into a circular coil of N2N_2 turns carrying the same current, the magnetic flux density at its centre becomes B2B_2. Prove that: B1B2=(N1N2)2\frac{B_1}{B_2}=(\frac{N_1}{N_2})^2

    Solve this question →

  4. A circular coil of radius 3.14 cm3.14\ cm, with a resistance of 2 Ω2\ \Omega per turn, has its ends connected to a DC source with a potential difference of 4 V4\ V between its terminals. Calculate the magnetic flux density at the centre of the coil.

    Solve this question →

  5. In the opposite circuit, a wire of resistance R is shaped into a circular half loop of radius 3.14 cm3.14\ cm, connected in series with a resistance of 3.72 Ω3.72\ \Omega, connecting wires of negligible resistance and a source of emf 24 V24\ V and internal resistance 2 Ω2\ \Omega. After closing switch K, the magnetic flux density at the centre of the half loop m due to the current in it is 2.4×10−5 T2.4\times10^{-5}\ T. Calculate the resistance of the wire (R). (given: π=3.14\pi=3.14)

    Figure of question 5Solve this question →

  6. An external magnetic field (B) of flux density 6×10−5 T6\times10^{-5}\ T acts perpendicular to the plane of a metal loop of radius 2π cm2\pi\ cm carrying a current I in the direction shown in the opposite figure. If the resultant magnetic flux density at the centre of the loop is 4×10−5 T4\times10^{-5}\ T in the direction of the external magnetic field B, calculate the current I.

    Figure of question 6Solve this question →

  7. Two concentric circular copper loops in the same plane each carry a current (I) as in the figure. What change must be made to the current in the inner loop to make the common centre of the two loops a neutral point? Explain your answer.

    Figure of question 7Solve this question →

  8. Two identical circular coils X and Y: coil Y is placed freely above coil X, and each coil carries a current I whose direction in the upper face of the two coils is as shown in the figure. Explain why coil Y did not fall and stayed suspended.

    Figure of question 8Solve this question →

  9. A metal loop carrying a current I has two straight wires in its plane, each carrying a current I, as in the opposite figure. Explain what happens to the magnitude of the resultant magnetic flux density at the centre of the loop (c) if the current is doubled in:
    (1) wire x only.
    (2) wire y only.

    Figure of question 9Solve this question →

  10. A solenoid with a resistance R per turn and length ℓ\ell has its ends connected to a DC source with a potential difference V between its terminals. Prove that the magnetic flux density at the middle of the coil on its axis is given by: B=μVℓRB=\frac{\mu V}{\ell R}

    Solve this question →

  11. An air-core solenoid carries a direct current. State four suggestions, each of which alone increases the magnetic flux density at the middle of the coil on its axis.

    Solve this question →

  12. Write the mathematical relation shown by each graph and what the slope of the straight line equals in each of the following:
    (where: (B) is the magnetic flux density, (r) the radius of the coil, (N) the number of turns of the coil, (ℓ)(\ell) the length of the solenoid)

    Figure of question 12Solve this question →

  13. A solenoid of resistance R with touching turns has its ends connected to a battery of negligible internal resistance. How is the magnetic flux density at a point at the middle of the coil on its axis affected by the following changes:
    (1) spreading the turns of the coil apart uniformly?
    (2) reshaping the turns of the coil by doubling their diameter while keeping them touching?
    (3) connecting an identical coil in series along the axis of the first coil so that they become one coil, keeping all the turns touching, and connecting the two free ends to the same battery?

    Solve this question →

  14. The opposite figure shows the magnetic field produced by a current in a solenoid:
    (1) Show with arrows on the figure the direction of the magnetic flux lines.
    (2) Why is the magnetic flux density outside the ends of the coil less than the magnetic flux density at a point at the middle of the coil on its axis?

    Figure of question 14Solve this question →

  15. In the opposite figure, explain why the lamp in circuit (1) goes out when switch K in circuit (2) is closed.

    Figure of question 15Solve this question →

  16. In the opposite figure, a solenoid carrying a current is wound around an iron rod. Explain why the iron rod is not magnetised.

    Figure of question 16Solve this question →

  17. In the opposite figure, a solenoid wound around a plastic cylinder is connected to an electric source and placed near a freely hanging magnet:
    (1) What type of magnetic force acts on the N pole of the magnet when switch K is closed?
    (2) What happens to the magnitude of the magnetic force when the plastic cylinder is replaced by one of soft iron and then the switch is closed?
    (3) What happens to the type of magnetic force between the coil and the magnet when the terminals of the source are reversed and then the switch is closed?

    Figure of question 17Solve this question →

  18. In the opposite figure, a solenoid is connected to a switch (K), a rheostat (S) and a cell. The coil is fixed above the pan of a balance on which a short magnet is placed with its upper face a north pole. Explain, with reasons, what happens to the balance reading after closing switch (K).

    Figure of question 18Solve this question →

  19. In the opposite circuit, the two solenoids x and y are identical except that coil x is made of aluminium and coil y of copper. Given that the resistivity of aluminium is greater than that of copper, what happens, when switch K connected to coil y is closed, to the direction of the resultant magnetic flux density at a point at the middle of the two coils on their axis (point p)?

    Figure of question 19Solve this question →

  20. A circular coil of diameter 12 cm12\ cm carries a current that produces a magnetic field at its centre. Its turns are spread apart uniformly along its axis to form a solenoid carrying the same current, and the magnetic flux density at a point inside it at the middle of its length on its axis becomes 14\frac{1}{4} of the magnetic flux density at the centre of the circular coil. Calculate the length of the solenoid.

    Solve this question →

Solve the essay questions online with explained answers →

From past exams

  1. The opposite figure shows two conductors (x) and (y). Conductor (x) carries a current I and conductor (y) carries a current of 2 A2\ A. The current (I) that makes the magnetic flux density at point M zero is .......... (Trial exam / May 2021)

    Figure of question 1
    1. A π2 A\frac{\pi}{2}\ A
    2. B π4 A\frac{\pi}{4}\ A
    3. C 2π A2\pi\ A
    4. D π A\pi\ A
    Solve this question →

  2. The following figure shows a wire shaped into circular half loops joined together, with its ends connected to a cell. At the centre of which loop is the magnetic flux density the smallest? (Trial exam / May, June 2021)

    Figure of question 2
    1. A A
    2. B B
    3. C C
    4. D D
    Solve this question →

  3. A straight wire is shaped into a circular coil of N turns carrying a current I. If it is reshaped so that its number of turns becomes N4\frac{N}{4} with the same current, the magnetic flux density at the centre of the circular coil becomes .......... its original value. (Trial exam / June 2021)

    1. A 116\frac{1}{16}
    2. B 16 times
    3. C 4 times
    4. D 14\frac{1}{4}
    Solve this question →

  4. A straight wire is made into a circular coil of (N) turns carrying a current (I), producing a magnetic flux of density (B) at the centre of the coil. If the same wire is reshaped into another circular coil of 2N3\frac{2N}{3} turns with the same current, the magnetic flux density at the centre of the coil becomes .......... (1st session 2021)

    1. A 23B\frac{2}{3}B
    2. B 29B\frac{2}{9}B
    3. C 19B\frac{1}{9}B
    4. D 49B\frac{4}{9}B
    Solve this question →

  5. In the following figure, two circular coils (y) and (x) have the same diameter and each carries the same current (I). If coil (x) has twice as many turns as coil (y), which of the following relations correctly expresses the magnetic flux density (B) at the centre of each coil? (1st session 2021)

    Figure of question 5
    1. A Bx=2ByB_x=2B_y
    2. B Bx=ByB_x=B_y
    3. C Bx=12ByB_x=\frac{1}{2}B_y
    4. D Bx=4ByB_x=4B_y
    Solve this question →

  6. Two circular loops with the same centre (m) and a straight wire all lie in the same plane, and each carries a current (I) as shown in the figure. The total magnetic flux density at the centre (m) due to the three currents equals .......... (1st session 2021)

    Figure of question 6
    1. A 0.83μIr\frac{0.83\mu I}{r}
    2. B 0.67μIr\frac{0.67\mu I}{r}
    3. C 0.54μIr\frac{0.54\mu I}{r}
    4. D 0.42μIr\frac{0.42\mu I}{r}
    Solve this question →

  7. A circular coil of N turns and radius r carries a current I, producing a magnetic flux of density B1B_1 at the centre. The coil is connected to another source, so a current three times the first flows and produces a magnetic flux of density B2B_2 at the centre. Then .......... (2nd session 2021)

    1. A B2=3B1B_2=3B_1
    2. B B2=B1B_2=B_1
    3. C B2=13B1B_2=\frac{1}{3}B_1
    4. D B2=32B1B_2=\frac{3}{2}B_1
    Solve this question →

  8. Two circular loops with the same centre (O) each carry a current I in the same direction as shown in the figure, so that the magnetic flux density due to the two currents at point (O) is B. If the current in one loop is reversed while the current in the other stays the same, the magnetic flux density at point (O) becomes .......... (2nd session 2021)

    Figure of question 8
    1. A B2\frac{B}{2}
    2. B B4\frac{B}{4}
    3. C B3\frac{B}{3}
    4. D B5\frac{B}{5}
    Solve this question →

  9. A circular coil of N turns and radius r carries a current I, producing a magnetic flux of density B at the centre. A quarter of its turns are cut off and the same current flows in the coil, so the magnetic flux density at the centre of the coil in the second case equals .......... (1st session 2022)

    1. A B
    2. B 34B\frac{3}{4}B
    3. C 32B\frac{3}{2}B
    4. D 43B\frac{4}{3}B
    Solve this question →

  10. Two circular coils with the same centre and the same number of turns but different radii carry currents I1I_1 and I2I_2 as shown in the figure. If the magnetic flux density due to the current of each coil at the common centre is (B), which of the following correctly expresses the relation between the values and directions of I1I_1 and I2I_2, and the resultant magnetic flux density due to them at the common centre (Bt)(B_t)? (2nd session 2022)

    Figure of question 10
    1. A I1=I2I_1=I_2 in the same direction, Bt=2BB_t=2B
    2. B I2=2I1I_2=2I_1 in opposite directions, Bt=0B_t=0
    3. C I2=I1I_2=I_1 in opposite directions, Bt=0B_t=0
    4. D I2=12I1I_2=\frac{1}{2}I_1 in the same direction, Bt=2BB_t=2B
    Solve this question →

  11. A metal loop carrying a current 2I produces a magnetic flux of density (B) at the centre of the loop (m). Then two straight wires (1) and (2) are placed touching the loop and in its plane as in the figure, and each carries a current. For the resultant magnetic flux density at point (m) to remain (B), the current in wire (2) must have a magnitude of .......... and a direction .......... (2nd session 2022)

    Figure of question 11
    1. A I, towards the top of the page
    2. B I, towards the bottom of the page
    3. C 2I, towards the bottom of the page
    4. D 2I, towards the top of the page
    Solve this question →

  12. Using the data shown in figures (1) and (2), which of the following correctly expresses the relation between the resultant magnetic flux densities at points C1C_1 and C2C_2? (1st session 2023)

    Figure of question 12
    1. A BC1=BC2=0B_{C_1}=B_{C_2}=0
    2. B BC1>BC2B_{C_1}>B_{C_2}
    3. C BC1=BC2≠0B_{C_1}=B_{C_2}\neq0
    4. D BC1<BC2B_{C_1}<B_{C_2}
    Solve this question →

  13. Each of the following figures shows two concentric metal loops in the same plane carrying two currents. In which figure is the resultant magnetic flux density at the centre of the two loops the greatest? (2nd session 2023)

    Figure of question 13
    1. A A
    2. B B
    3. C C
    4. D D
    Solve this question →

  14. A circular coil of 100 turns carries a current of 5 A5\ A. If the radius of the coil is 2π cm2\pi\ cm, the magnetic flux density at the centre of the coil = .......... (2nd session 2024)

    1. A 2×10−3 T2\times10^{-3}\ T
    2. B 2 T2\ T
    3. C 5 T5\ T
    4. D 5×10−3 T5\times10^{-3}\ T
    Solve this question →

  15. In the opposite figure, two concentric circular coils lie in the plane of the page. The outer coil has a radius of 20 cm20\ cm, 100 turns and carries a current of 4 A4\ A, and the inner coil has a radius of 10 cm10\ cm, 50 turns and carries a current of 2 A2\ A. The resultant magnetic flux density at their common centre equals .......... (Sample exam 2025)

    Figure of question 15
    1. A 6.28×10−4 T6.28\times10^{-4}\ T
    2. B 8.42×10−4 T8.42\times10^{-4}\ T
    3. C 7.36×10−5 T7.36\times10^{-5}\ T
    4. D 9.63×10−5 T9.63\times10^{-5}\ T
    Solve this question →

  16. A straight wire is shaped as in the opposite figure. The radius of the circular part is π cm\pi\ cm and a current of 10 A10\ A flows in the wire. If the wire is placed in an external magnetic field perpendicular to its plane with a flux density of 1.5×10−4 T1.5\times10^{-4}\ T, the resultant magnetic flux density at the centre (C) equals .......... (Sample exam 2025)

    Figure of question 16
    1. A 0
    2. B 3×10−4 T3\times10^{-4}\ T
    3. C 3.5×10−4 T3.5\times10^{-4}\ T
    4. D 4.5×10−4 T4.5\times10^{-4}\ T
    Solve this question →

  17. A circular coil of 50 turns carrying a current of 1.4 A1.4\ A has its axis along the Earth's magnetic field, whose flux density is 5×10−5 T5\times10^{-5}\ T. If the coil is turned over, the total magnetic flux density at the centre of the circular coil becomes twice what it was at first. The radius of the coil equals .......... (Sample exam 2025)
    (given: the magnetic field due to the current in the circular coil is greater than the Earth's magnetic field, and the magnetic permeability =12.56×10−7 Wb/A.m=12.56\times10^{-7}\ Wb/A.m)

    1. A 2.93 m2.93\ m
    2. B 8.8 m8.8\ m
    3. C 0.88 m0.88\ m
    4. D 0.293 m0.293\ m
    Solve this question →

  18. In the opposite figure, an insulated circular loop carries a current (I) and an insulated long straight wire carries a current (I), both in the same plane. If the resultant magnetic flux density at the centre of the loop (c) is zero, the distance (d) equals .......... (Sample exam 2025)

    Figure of question 18
    1. A 3.14 cm3.14\ cm
    2. B 6.28 cm6.28\ cm
    3. C 3.18 cm3.18\ cm
    4. D 5 cm5\ cm
    Solve this question →

  19. An insulated straight wire is placed touching a metal loop and in its plane. If the wire and the loop each carry a current (I) in the directions shown in the figure, the direction of the resultant magnetic flux density at the centre of the loop (c) is .......... (1st session 2025)

    Figure of question 19
    1. A perpendicular to the diameter (xy), in the plane of the loop
    2. B perpendicular to the plane of the loop, into it
    3. C along the diameter (xy)
    4. D perpendicular to the plane of the loop, out of it
    Solve this question →

  20. A metal loop of mean diameter 10 cm10\ cm and resistance (R) receives a current of 6 A6\ A through two terminals (x) and (y). An insulated straight wire touches the loop, lies in its plane and carries a current of 2 A2\ A as shown in the figure. What is the resultant magnetic flux density at the centre of the loop (c)? (1st session 2025)

    Figure of question 20
    1. A 4×10−6 T4\times10^{-6}\ T
    2. B 8×10−6 T8\times10^{-6}\ T
    3. C 1.6×10−5 T1.6\times10^{-5}\ T
    4. D 3.2×10−5 T3.2\times10^{-5}\ T
    Solve this question →

  21. A circular coil of insulated wire wound around a soft iron core carries an electric current. The magnetic flux density at the centre of the coil doubles when .......... (2nd session 2025)

    1. A the number of turns of the coil is halved
    2. B the radius of the coil is doubled
    3. C the current in the coil is doubled
    4. D the iron core is removed from the coil
    Solve this question →

  22. In the figure shown, a half loop carries a current (I) and is placed in a uniform external magnetic field of flux density (B) directed perpendicular to the page and outwards. If the resultant magnetic flux density at point (Y) is perpendicular to the page and outwards, which of the following relations is correct? (Sample exam 2026)

    Figure of question 22
    1. A B<μI8rB<\frac{\mu I}{8r}
    2. B B=μI8rB=\frac{\mu I}{8r}
    3. C B<μI4rB<\frac{\mu I}{4r}
    4. D B>μI4rB>\frac{\mu I}{4r}
    Solve this question →

  23. The figure shows an insulated long straight wire placed touching a metal half loop, and each carries a direct current. The direction of the resultant magnetic field due to the two currents at point (P) is .......... (Sample exam 2026)

    Figure of question 23
    1. A perpendicular to the page, inwards
    2. B perpendicular to the page, outwards
    3. C parallel to the page, to the right
    4. D parallel to the page, to the left
    Solve this question →

  24. The figure shows a solenoid carrying a current I, of length ℓ\ell, turn area A and N turns. If its turns are spread apart until its length becomes 3ℓ3\ell, the magnetic flux density at any point inside it on its axis .......... (Trial exam / May 2021)

    Figure of question 24
    1. A drops to 13\frac{1}{3} of its original value
    2. B drops to 16\frac{1}{6} of its original value
    3. C drops to 19\frac{1}{9} of its original value
    4. D drops to 112\frac{1}{12} of its original value
    Solve this question →

  25. You have several conductors, each carrying a current (I), as in the following figures. Which of the following relations is correct? (1st session 2022)

    Figure of question 25
    1. A Z>YZ>Y
    2. B X=ZX=Z
    3. C Y<XY<X
    4. D X=YX=Y
    Solve this question →

  26. A solenoid 20 cm20\ cm long has 100 turns, each of radius 0.1 m0.1\ m, and carries a current of 4.9 A4.9\ A; the permeability of the medium inside it is 887×10−7 Wb/A.m\frac{88}{7}\times10^{-7}\ Wb/A.m. The magnetic flux through a cross-section of the coil at its middle is .......... (given: π=227\pi=\frac{22}{7}) (Trial exam 2023)

    1. A 6.166×10−6 Wb6.166\times10^{-6}\ Wb
    2. B 30.8×10−4 Wb30.8\times10^{-4}\ Wb
    3. C 6.166×10−3 Wb6.166\times10^{-3}\ Wb
    4. D 9.68×10−5 Wb9.68\times10^{-5}\ Wb
    Solve this question →

  27. A solenoid of insulated copper wire carries a current (I), and the magnetic flux density at the middle of its length on its axis is (B). When its turns are spread apart uniformly, the magnetic flux density at the middle of its length on its axis becomes (14B)(\frac{1}{4}B). If the flux density is brought back to its first value (B) by increasing the current in the coil by 3 A3\ A, the current (I) equals .......... (Trial exam 2023)

    1. A 1 A1\ A
    2. B 2 A2\ A
    3. C 3 A3\ A
    4. D 4 A4\ A
    Solve this question →

  28. The graph shows the relation between the magnetic flux density (B) at the middle of the axis of each of several solenoids (L, M, N, O) and the current (I) in each. If the coils have the same number of turns and the same permeability of the medium, the shortest coil is coil .......... (1st session 2023)

    Figure of question 28
    1. A N
    2. B L
    3. C M
    4. D O
    Solve this question →

  29. In the opposite figure, a solenoid of length ℓ\ell and N turns carries a current I. In front of it, a long straight wire carrying a current I is placed perpendicular to the axis of the solenoid. The resultant magnetic flux density due to the two currents at point (M) is .......... (1st session 2024)
    (where BsB_s is for the solenoid and BwB_w for the wire)

    Figure of question 29
    1. A Bs2−Bw2\sqrt{B_s^2-B_w^2}
    2. B Bs2−Bw2B_s^2-B_w^2
    3. C Bw2+Bs2\sqrt{B_w^2+B_s^2}
    4. D Bw2+Bs2B_w^2+B_s^2
    Solve this question →

  30. The opposite figure shows a solenoid and a straight wire, each carrying a current; the wire is at a distance d from point z at the middle of the coil. The magnetic flux densities due to the coil's current alone and the wire's current alone at point z are B and 43B\frac{4}{3}B respectively, and the resultant magnetic flux density at point z due to both is B1B_1. If the distance between the wire and point z is increased to 2d, the resultant magnetic flux density at point z becomes B2B_2. Then .......... (1st session 2024)

    Figure of question 30
    1. A B2=1.4B1B_2=1.4B_1
    2. B B2=0.72B1B_2=0.72B_1
    3. C B2=1.6B1B_2=1.6B_1
    4. D B2=0.5B1B_2=0.5B_1
    Solve this question →

  31. What happens when switch K in the figure shown is closed? (1st session 2024)

    Figure of question 31
    1. A Magnet (2) moves towards the coil while magnet (1) moves away from the coil
    2. B Both magnets (1) and (2) move towards the coil
    3. C Magnet (1) moves towards the coil while magnet (2) moves away from the coil
    4. D Both magnets (1) and (2) move away from the coil
    Solve this question →

  32. A solenoid of 14 turns and length 22 cm22\ cm carries a current of 2 A2\ A. The magnetic flux density at a point on its axis at the middle of the coil = .......... (μ=887×10−7 T.m/A)(\mu=\frac{88}{7}\times10^{-7}\ T.m/A) (2nd session 2024)

    1. A 16×10−7 T16\times10^{-7}\ T
    2. B 1.6×10−4 T1.6\times10^{-4}\ T
    3. C 8×10−4 T8\times10^{-4}\ T
    4. D 8×10−7 T8\times10^{-7}\ T
    Solve this question →

  33. In the opposite figure, if the magnetic flux density due to each of wire (X), wire (Y) and the solenoid alone at point (A) is (B), which of the following is the resultant magnetic flux density at the same point when the current in one of the wires is reversed? (2nd session 2024)

    Figure of question 33
    1. A 3B\sqrt{3}B
    2. B 5B
    3. C 5B\sqrt{5}B
    4. D 3B
    Solve this question →

  34. In the opposite figure, a long solenoid with 5 turns/cm of its length has a circular coil of radius π5 cm\frac{\pi}{5}\ cm and 10 turns wound around its middle so that the axes of the two coils coincide. If a current of 4 A4\ A flows in each coil, the resultant magnetic flux density at the common centre of the two coils (m) equals .......... (Sample exam 2025)

    Figure of question 34
    1. A 4×10−3 T4\times10^{-3}\ T
    2. B 2.5×10−3 T2.5\times10^{-3}\ T
    3. C 1.5×10−3 T1.5\times10^{-3}\ T
    4. D 6.5×10−3 T6.5\times10^{-3}\ T
    Solve this question →

  35. In the opposite figure, a solenoid with 300 turns/m carries a current of 1.75 A1.75\ A, and a straight wire parallel to the axis of the solenoid is placed next to it. If the magnetic flux density due to the current in the straight wire at point (c), at the middle of the solenoid, is 2.33×10−4 T2.33\times10^{-4}\ T, the resultant magnetic flux density at point (c) is approximately .......... (Sample exam 2025)

    Figure of question 35
    1. A 4.27×10−4 T4.27\times10^{-4}\ T
    2. B 6.44×10−4 T6.44\times10^{-4}\ T
    3. C 7×10−4 T7\times10^{-4}\ T
    4. D 8.93×10−4 T8.93\times10^{-4}\ T
    Solve this question →

  36. Which of the following figures correctly describes the direction of the magnetic field produced by a current in a solenoid? (Sample exam 2025)

    Figure of question 36
    1. A A
    2. B B
    3. C C
    4. D D
    Solve this question →

  37. A solenoid of resistance 0.5R0.5R is part of an electric circuit as shown in the opposite figure. The magnetic flux density at the middle of the coil on its axis is greatest after closing switch .......... only. (Sample exam 2025)

    Figure of question 37
    1. A K1K_1
    2. B K2K_2
    3. C K3K_3
    4. D K4K_4
    Solve this question →

  38. The figure shows two insulated solenoids of negligible resistance with the same number of turns, each wound around a metal core of the same type and connected to a source of negligible internal resistance and a resistor. If the magnetic flux densities at the middle of each coil on its axis are equal, and the length of each coil is very large compared with its diameter, the ratio of the emfs of the two sources (VB)1(VB)2\frac{(V_B)_1}{(V_B)_2} = .......... (Sample exam 2025)

    Figure of question 38
    1. A 23\frac{2}{3}
    2. B 112\frac{1}{12}
    3. C 14\frac{1}{4}
    4. D 12\frac{1}{2}
    Solve this question →

  39. You have a solenoid of length (ℓ)(\ell) with its turns uniformly distributed along its length, and its ends connected to the terminals of a battery (VB)(V_B) of negligible internal resistance. When half of the coil is cut off and the rest is connected to the same battery, which of the following physical quantities is halved? (1st session 2025)

    1. A The number of turns per unit length of the coil
    2. B The ohmic resistance of the coil
    3. C The current in the coil
    4. D The magnetic flux density at the middle of the coil
    Solve this question →

  40. A circular coil of radius 10 cm10\ cm and 14 turns is wound around the middle of an insulated solenoid of 28 turns uniformly distributed over 10 cm10\ cm. The axis of the solenoid is perpendicular to the plane of the circular coil and passes through its centre. The circular coil carries a current of 2 A2\ A in the direction shown in the figure. What are the magnitude and direction of the current in the solenoid that make the magnetic flux density at the centre of the circular coil zero? (2nd session 2025)

    Figure of question 40
    1. A 2 A2\ A, opposite to the current in the circular coil
    2. B 0.5 A0.5\ A, in the same direction as the current in the circular coil
    3. C 2 A2\ A, in the same direction as the current in the circular coil
    4. D 0.5 A0.5\ A, opposite to the current in the circular coil
    Solve this question →

  41. The figure shows a battery of negligible internal resistance connected to a resistor (R), a solenoid of ohmic resistance (R) and a lamp (X) whose filament has a resistance (R). If the filament of lamp (X) burns out, the magnetic flux density at the middle of the solenoid .......... (Sample exam 2026)

    Figure of question 41
    1. A decreases
    2. B increases
    3. C becomes zero
    4. D does not change
    Solve this question →

  42. A solenoid connected to a battery of emf (VB)(V_B) with negligible internal resistance and a rheostat carries a current that produces a magnetic field of flux density (B) at the middle of the coil on its axis. The coil is placed in an external magnetic field of flux density (1.5B) directed to the right of the page as in the opposite figure. When the resistance taken from the rheostat is increased by one third of its first value, the resultant magnetic flux density at point (C) .......... (neglecting the resistance of the solenoid wire) (Sample exam 2026)

    Figure of question 42
    1. A increases
    2. B decreases
    3. C stays the same
    4. D becomes zero
    Solve this question →

  43. A solenoid is connected to a battery of emf (VB)(V_B) and internal resistance (r) and a rheostat as in the opposite figure. When the slider is moved from position (X) to position (Y), the magnetic flux density at a point at the middle of the solenoid .......... (Sample exam 2026)

    Figure of question 43
    1. A increases
    2. B does not change
    3. C decreases but does not become zero
    4. D becomes zero
    Solve this question →

Solve the past exam questions online with explained answers →

Other lessons in Magnetic Effect of Electric Current and Measuring Instruments

← كل دروس بنك الأسئلة