Black Body Radiation questions

In the electromagnetic spectrum, the ratio between the wavelength of red light and the wavelength of ultraviolet rays is ..........

1. A greater than one
2. B less than one
3. C equal to one
4. D equal to the ratio between the speeds of the two radiations

In the opposite figure, when the lamp is switched on for a certain time, which of the two surfaces A or B gets hotter?

1. A Surface A
2. B Surface B
3. C Both surfaces reach the same temperature
4. D The answer cannot be determined

The dominant colour of the electromagnetic radiation emitted by an ideal black body changes with the ..........

1. A mass of the body
2. B density of the body's material
3. C temperature of the body
4. D type of the body's material

The opposite figure shows a heated piece of iron. Which position on the piece has the lowest temperature?

1. A A
2. B B
3. C C
4. D D

Which of the following graphs represents Planck's curve for the radiation emitted by two identical bodies x and y kept at constant temperatures $T_x$ and $T_y$ respectively, where $(T_y < T_x)$?

1. A A
2. B B
3. C C
4. D D

In Planck's curve for black body radiation, if the temperature of the body decreases, then ..........

1. A the peak of the curve: shifts to higher frequencies, the area under the curve: increases
2. B the peak of the curve: shifts to higher frequencies, the area under the curve: decreases
3. C the peak of the curve: shifts to lower frequencies, the area under the curve: increases
4. D the peak of the curve: shifts to lower frequencies, the area under the curve: decreases

An AC circuit consists of an AC source connected to a lamp and an induction coil with an iron rod inside it, as in the opposite figure. The wavelength $(\lambda_o)$ in the radiation emitted by the lamp has the maximum intensity $(I_o)$. If the iron rod is taken out of the coil, then ..........

1. A maximum radiation intensity: stays $I_o$, wavelength at maximum intensity: stays $\lambda_o$
2. B maximum radiation intensity: stays $I_o$, wavelength at maximum intensity: becomes less than $\lambda_o$
3. C maximum radiation intensity: becomes more than $I_o$, wavelength at maximum intensity: stays $\lambda_o$
4. D maximum radiation intensity: becomes more than $I_o$, wavelength at maximum intensity: becomes less than $\lambda_o$

Two identical bodies x and y, the temperature of x is higher than that of y. The ratio between the rate of total radiated energy from x and that from y is ..........

1. A less than one
2. B equal to one
3. C greater than one
4. D the information is not enough to decide

In Planck's curve for black body radiation, the radiation intensity at very high frequencies ..........

1. A does not change
2. B is medium
3. C is very large
4. D approaches zero

In the opposite graph, if $\lambda_1$ is the shortest wavelength of visible light and $\lambda_2$ is the longest wavelength of visible light, the graph may represent the radiation emitted by ..........

1. A a glowing star
2. B the Earth
3. C a tungsten lamp
4. D the human body

The opposite graph represents Planck's curve for a hot black body. What happens to each of the following when its temperature is raised:
(1) the number of photons emitted by the body per second?

1. A increases
2. B decreases
3. C does not change
4. D cannot be determined

The opposite graph represents Planck's curve for a hot black body. What happens to each of the following when its temperature is raised:
(2) the value of the maximum radiation intensity?

1. A becomes greater than I
2. B becomes less than I
3. C stays I
4. D cannot be determined

The opposite graph represents Planck's curve for the radiation of a hot ideal black body. The rate of emission of photons of wavelength $(\lambda_1)$ compared to their rate of emission at wavelength $(\lambda_2)$ is ..........

1. A greater
2. B smaller
3. C equal
4. D cannot be determined

The opposite graph represents Planck's curve for the radiation of an ideal black body. Which of the two regions shown has an explanation that contradicts the principles of classical physics?

1. A Region A
2. B Region B
3. C Both regions
4. D Neither region

The opposite figure shows a glowing electric lamp. The ratio between the total energy of the invisible rays it emits and the total energy of the visible rays in the same time is ..........

1. A greater than one
2. B less than one
3. C equal to one
4. D unchanged when the temperature changes

Which of the following graphs represents the relation between the wavelength $(\lambda_m)$ at maximum radiation intensity emitted by several identical hot bodies and the absolute temperature (T) of each?

1. A A
2. B B
3. C C
4. D D

The opposite figure shows Planck's curve of a hot black body at two temperatures $T_1$ and $T_2$. The ratio $\left(\frac{\lambda_1}{\lambda_2}\right)$ is ..........

1. A $\dfrac{1}{16}$
2. B $\dfrac{1}{8}$
3. C $\dfrac{1}{4}$
4. D $\dfrac{1}{2}$

A black body has a temperature of 3000 K and the wavelength of maximum radiation intensity is λ. If it is cooled to an absolute temperature T, the wavelength of maximum radiation intensity becomes 10 λ. The temperature T equals ..........

1. A 300 K
2. B 2700 K
3. C 270 K
4. D 1800 K

The figure in front of you shows the relation between the intensity of radiation emitted from the surfaces of the Sun and the Earth and the wavelength (λ). If the temperature of the Sun's surface is 6000 K, then using the data on the figure, the average temperature of the Earth's surface is ..........

1. A 9000 K
2. B 1935.9 K
3. C 309.9 K
4. D 200 K

For a black body at absolute temperature $(T_o)$, the wavelength at maximum radiation intensity is $(\lambda_o)$. If the temperature of the body is raised by 500 K, the wavelength at maximum radiation intensity decreases by $\left(\frac{5}{8}\lambda_o\right)$. The temperature $(T_o)$ equals ..........

1. A 300 K
2. B 500 K
3. C 800 K
4. D 1500 K

The opposite graph represents the relation between the wavelength $(\lambda_m)$ at maximum radiation intensity emitted by a number of hot bodies and the reciprocal of the absolute temperature $\left(\frac{1}{T}\right)$ of each. The wavelength at maximum radiation intensity emitted by a body at 4830 K lies in the range of ..........

1. A infrared rays
2. B visible light
3. C ultraviolet rays
4. D X-rays

The opposite figure shows a picture taken by a night vision device. The device depends on receiving the .......... rays emitted by bodies.

1. A visible
2. B ultraviolet
3. C infrared
4. D X

According to the assumptions of Max Planck's quantum theory:
(1) the atoms of a black body emit photons ..........

1. A when they move from their ground level to a higher energy level
2. B of different wavelengths but the same intensity
3. C whose number decreases as the frequency of the radiation increases beyond a certain limit
4. D whose energy is directly proportional to the wavelength of the radiation

According to the assumptions of Max Planck's quantum theory:
(2) when an atom moves from a higher energy level to a lower energy level, it ..........

1. A absorbs a photon of energy hν
2. B absorbs a photon of energy $h\nu^2$
3. C emits a photon of energy hν
4. D emits a photon of energy $h\nu^2$

According to the assumptions of Max Planck's quantum theory:
(3) the energy of a photon of frequency $5 \times 10^{14}$ Hz equals ..........

1. A $1.7 \times 10^{-19}$ J
2. B $3.3 \times 10^{-19}$ J
3. C $6.6 \times 10^{-19}$ J
4. D $9.9 \times 10^{-19}$ J

One of the properties of cathode rays is that they are ..........

1. A electromagnetic waves
2. B of constant speed
3. C charged particles
4. D uncharged particles

The opposite figure represents a cathode ray tube. Which of the parts in the tube:
(1) is the source of electrons?

1. A Part (1)
2. B Part (2)
3. C Part (3)
4. D Part (4)

The opposite figure represents a cathode ray tube. Which of the parts in the tube:
(2) is responsible for changing the position where the electron beam hits the screen?

1. A Part (1)
2. B Part (2)
3. C Part (3)
4. D Part (4)

The opposite figure represents a cathode ray tube. Which of the parts in the tube:
(3) controls the brightness on the fluorescent screen?

1. A Part (1)
2. B Part (2)
3. C Part (3)
4. D Part (4)

Which figure shows the correct electric potentials used to form an image on the screen of a cathode ray tube?

1. A A
2. B B
3. C C
4. D D

In a cathode ray tube, when the grid potential is changed from −20 V to −50 V ..........

1. A the brightness on the fluorescent screen increases
2. B the brightness on the fluorescent screen decreases
3. C the deflection of the electron beam increases
4. D the deflection of the electron beam decreases

In a cathode ray tube, when the filament is damaged ..........

1. A the brightness on the fluorescent screen increases
2. B the brightness on the fluorescent screen decreases
3. C the fluorescent screen does not light up
4. D the deflection of the electron beam decreases

In a cathode ray tube, when the grid is not connected to any electric signal ..........

1. A the path of the electron beam to the screen cannot be controlled
2. B the fluorescent screen does not light up
3. C the electron beam goes back to the cathode
4. D the brightness on the screen stays almost constant

Which of the following choices shows what appears on the screen of a cathode ray tube when the beam-moving system is not working?

1. A A
2. B B
3. C C
4. D D

What happens to the path of the cathode rays when a DC voltage is connected across part (X)?

1. A The electron beam is deflected towards the negative plate
2. B The electron beam is deflected towards the positive plate
3. C The electron beam is not deflected
4. D The electron beam does not pass through part (X)

The kinetic energy of the electrons when they reach the anode in a cathode ray tube depends on ..........

1. A the surface area of the cathode
2. B the type of the anode material
3. C the potential difference between the two plates of the beam-directing system
4. D the potential difference between the anode and the cathode

In a cathode ray tube, if the potential difference between the anode and the cathode increases while the temperature of the filament does not change, the rate of emission of electrons from the filament ..........

1. A increases
2. B decreases
3. C does not change
4. D cannot be determined

In a cathode ray tube, the maximum speed of an electron reaches v when it is accelerated by a potential difference V. If the potential difference acting on the electron increases to 2 V, the maximum speed of the electron becomes ..........

1. A 2 v
2. B $\sqrt{2}$ v
3. C 4 v
4. D $\dfrac{1}{2}$ v

The graph that represents the relation between the square of the maximum speed $(v^2)$ of the electrons reaching the anode in a cathode ray tube and the potential difference (V) between the anode and the cathode is ..........

1. A A
2. B B
3. C C
4. D D

If the potential difference between the anode and the cathode in a cathode ray tube is 1000 V:
(1) the maximum kinetic energy of the electrons is ..........

1. A $1.6 \times 10^{-15}$ J
2. B $1.6 \times 10^{-16}$ J
3. C $1.6 \times 10^{-17}$ J
4. D $32 \times 10^{-18}$ J

If the potential difference between the anode and the cathode in a cathode ray tube is 1000 V:
(2) the maximum speed of an electron emitted from the cathode when it reaches the anode equals ..........

1. A $1.88 \times 10^{6}$ m/s
2. B $1.88 \times 10^{7}$ m/s
3. C $3.52 \times 10^{5}$ m/s
4. D $3.52 \times 10^{4}$ m/s

The emission of electrons from the cathode surface of a photoelectric cell depends on ..........

1. A the type of the anode material and the intensity of the incident light
2. B the type of the cathode material and the frequency of the incident light
3. C the type of the anode material and the frequency of the incident light
4. D the type of the cathode material and the intensity of the incident light

Which of the following graphs represents the relation between the maximum kinetic energy $(KE)_{max}$ of the electrons emitted from the cathode of a photoelectric cell and the intensity of the monochromatic light falling on the cathode?

1. A A
2. B B
3. C C
4. D D

Electromagnetic radiation of a certain frequency fell on the cathode of a photoelectric cell and electrons were emitted with a certain maximum kinetic energy. Then the radiation was replaced by radiation of a higher frequency. The quantity that does not change is ..........

1. A the energy of the incident photon
2. B the speed of the incident photon
3. C the maximum energy of the emitted electron
4. D the maximum speed of the emitted electron

In the photoelectric effect, if the energy of the photon falling on the metal surface is $(E_1)$ and the kinetic energy of the electron it frees from the surface is $(E_2)$, the ratio $\left(\frac{E_1}{E_2}\right)$ is ..........

1. A greater than one
2. B less than one
3. C equal to one
4. D undefined

In a photoelectric cell experiment, the cathode surface was lit with monochromatic light whose frequency is greater than the threshold frequency of the metal. Then the experiment was repeated using light of the same wavelength but with twice the light intensity. The quantity that doubles is ..........

1. A the energy of one photon
2. B the maximum kinetic energy of the emitted electrons
3. C the work function of the metal
4. D the photoelectric current

When a light beam of wavelength 591.5 nm falls on a caesium surface, photoelectrons are only just emitted. For electrons of energy 1.81 eV to be emitted, a beam of wavelength of about .......... is needed.

1. A 318 nm
2. B 520 nm
3. C 650 nm
4. D 720 nm

When monochromatic electromagnetic radiation falls on the cathode of a photoelectric cell, a photoelectric current passes in its circuit. The rate of emission of electrons from the cathode decreases but does not stop when .......... is decreased.

1. A the wavelength of the incident light
2. B the frequency of the incident light
3. C the speed of the incident light
4. D the intensity of the incident light

Which of the following factors controls the rate of emission of electrons from a metal surface when photons with a wavelength shorter than the threshold wavelength of the surface fall on it?

1. A The frequency of the photon beam
2. B The energy of the photon
3. C The intensity of the photon beam
4. D The momentum of the photon

Monochromatic light fell on a metal surface and electrons were freed at a certain rate. If another monochromatic light of higher frequency falls on the same metal at the same rate, the number of electrons freed per second ..........

1. A increases
2. B decreases
3. C does not change
4. D cannot be determined

The opposite figure shows light from an electric lamp falling on a photoelectric cell, causing a photoelectric current. If the brightness of the lamp increases, the photoelectric current ..........

1. A increases
2. B decreases but does not stop
3. C does not change
4. D stops

In the opposite figure, a glowing black body was placed in front of a metal surface, and the radiation from the black body caused electrons to be emitted from the metal surface. If the temperature of the black body is raised:
(1) the rate of emission of electrons from the metal surface ..........

1. A increases
2. B decreases
3. C does not change
4. D stops

In the opposite figure, a glowing black body was placed in front of a metal surface, and the radiation from the black body caused electrons to be emitted from the metal surface. If the temperature of the black body is raised:
(2) the maximum kinetic energy of the electrons emitted from the metal surface ..........

1. A increases
2. B decreases
3. C does not change
4. D becomes zero

If the frequency of the light falling on a metal surface doubles, the work function of this metal ..........

1. A doubles
2. B becomes half
3. C stays constant
4. D becomes four times

Which of the following graphs represents the relation between the maximum kinetic energy of the photoelectrons $(KE)_{max}$ and the reciprocal of the wavelength of the rays falling on the cathode of the photoelectric cell $\left(\frac{1}{\lambda}\right)$?

1. A A
2. B B
3. C C
4. D D

Light fell on a metal surface with a frequency greater than the threshold frequency of the surface. Which of the following graphs represents the relation between the speed (v) of the emitted electrons and the rate at which photons fall on the surface $\left(\frac{N}{t}\right)$?

1. A A
2. B B
3. C C
4. D D

When light falls on a metal surface with a frequency less than the threshold frequency of the surface, which of the following graphs represents the relation between the rate of emission of electrons $\left(\frac{N_2}{t}\right)$ from the surface and the rate at which photons fall on it $\left(\frac{N_1}{t}\right)$?

1. A A
2. B B
3. C C
4. D D

When light falls on a metal surface with a frequency greater than the threshold frequency of the surface, which of the following graphs represents the relation between the rate of emission of electrons $\left(\frac{N_2}{t}\right)$ from the surface and the rate at which photons fall on it $\left(\frac{N_1}{t}\right)$?

1. A A
2. B B
3. C C
4. D D

The opposite graph represents the relation between the maximum kinetic energy $(KE)_{max}$ of the electrons emitted from the cathode of a photoelectric cell and the frequency of the incident light (ν). The value a divided by the value b represents ..........

1. A Planck's constant
2. B the threshold frequency
3. C the work function
4. D the photon energy

The opposite figure represents the relation between the frequency of the light falling on the surfaces of three metals A, B, D and the maximum kinetic energy of the electrons emitted from them. If the work functions of these metals are $E_A$, $E_B$, $E_D$, then ..........

1. A $E_A < E_B < E_D$
2. B $E_A = E_B < E_D$
3. C $E_A > E_B > E_D$
4. D $E_A = E_B = E_D$

Three metal surfaces (x), (y), (z): surfaces (x) and (y) are caesium and surface (z) is silver. Electromagnetic radiation of wavelengths λ, $\frac{2}{3}$ λ and λ fell on them respectively, and photoelectrons were emitted from all three surfaces. Given that the work function of caesium is less than that of silver, the correct order of the three surfaces by the maximum speed of the electrons emitted from them is ..........

1. A z < y < x
2. B z > y > x
3. C x = z < y
4. D z < x < y

Given that the work functions of potassium and silver are 1.8 eV and 4.73 eV respectively, which of the following graphs represents the relation between the maximum kinetic energy $(KE)_{max}$ of the electrons emitted from each and the frequency (ν) of the light falling on each?

1. A A
2. B B
3. C C
4. D D

The opposite graph represents the relation between the maximum kinetic energy $(KE)_{max}$ of the electrons emitted from two metal surfaces (1) and (2) and the wavelength (λ) of the photons falling on each. Which metal has the larger work function?

1. A Metal (1)
2. B Metal (2)
3. C Both metals have the same work function
4. D The answer cannot be determined

The opposite figure shows the relation between the maximum kinetic energy of the electrons emitted from the cathode surface of a photoelectric cell and the frequency of the light falling on it. Which of the following quantities gives Planck's constant?

1. A D
2. B $\dfrac{D}{B + A}$
3. C $\dfrac{A}{B}$
4. D $\dfrac{C}{B - A}$

The opposite graph represents the relation between the maximum kinetic energy $(KE)_{max}$ of the electrons emitted from a metal surface and the frequency (ν) of the incident light. The ratio $\left(\frac{E_1}{E_2}\right)$ equals ..........

1. A $\dfrac{1}{2}$
2. B $\dfrac{1}{3}$
3. C $\dfrac{1}{4}$
4. D $\dfrac{1}{5}$

Monochromatic electromagnetic radiation fell on a metal surface whose work function is 3 eV. Which of the following choices can represent the energy of the incident photon and the maximum kinetic energy of the electrons emitted?

1. A incident photon energy: 2 eV, maximum kinetic energy of the electrons: 1 eV
2. B incident photon energy: 2 eV, maximum kinetic energy of the electrons: 5 eV
3. C incident photon energy: 4 eV, maximum kinetic energy of the electrons: 1 eV
4. D incident photon energy: 4 eV, maximum kinetic energy of the electrons: 2 eV

Electromagnetic radiation of frequency ν fell on a metal surface whose work function is 3 eV, and electrons were emitted with a maximum kinetic energy of 2 eV. If the radiation is replaced by another of frequency 2 ν, the maximum kinetic energy of the emitted electrons equals ..........

1. A 7 eV
2. B 6 eV
3. C 5 eV
4. D 4 eV

A metal surface has a threshold frequency $\nu_c$. A light beam of frequency $5\nu_c$ fell on it and photoelectrons were emitted with a maximum speed of $8 \times 10^6$ m/s. If the frequency of the incident light becomes $2\nu_c$, the maximum speed of the emitted electrons becomes ..........

1. A $6 \times 10^{6}$ m/s
2. B $4 \times 10^{6}$ m/s
3. C $8 \times 10^{6}$ m/s
4. D $1 \times 10^{6}$ m/s

Monochromatic electromagnetic radiation fell on each of two metal surfaces (x) and (y) whose work functions are 3 eV and 4 eV respectively. The maximum kinetic energies of the electrons emitted from the two surfaces respectively can be ..........

1. A (x): 1 eV, (y): 2 eV
2. B (x): 2 eV, (y): 1 eV
3. C (x): 3 eV, (y): 1 eV
4. D (x): 2 eV, (y): 2 eV

In the photoelectric cell experiment, using electromagnetic radiation of wavelength λ, the maximum kinetic energy of the emitted electrons was KE. If another radiation of wavelength $\frac{\lambda}{2}$ is used, the maximum kinetic energy of the emitted electrons becomes ..........

1. A zero
2. B less than 2 KE and greater than KE
3. C 2 KE
4. D greater than 2 KE

When light of wavelength 623 nm falls on a metal surface, electrons are freed with a speed of $4.6 \times 10^5$ m/s:
(1) the work function of this surface equals ..........

1. A $2.23 \times 10^{-19}$ J
2. B $3.19 \times 10^{-19}$ J
3. C $4.15 \times 10^{-19}$ J
4. D $4.6 \times 10^{-19}$ J

When light of wavelength 623 nm falls on a metal surface, electrons are freed with a speed of $4.6 \times 10^5$ m/s:
(2) the threshold frequency of this surface equals ..........

1. A $6.94 \times 10^{14}$ Hz
2. B $6.26 \times 10^{14}$ Hz
3. C $4.81 \times 10^{14}$ Hz
4. D $3.37 \times 10^{14}$ Hz

In a photoelectric cell, when yellow light falls on the cathode surface no electrons are emitted, while when blue light falls on it electrons are emitted at a certain rate. If red light falls on the same cathode surface, the rate of emission of electrons ..........

1. A increases
2. B decreases but does not stop
3. C becomes zero
4. D does not change

If the threshold frequency of a metal surface lies within the frequencies of blue light, the rays falling on this metal that allow electrons to be emitted from it are in the region of .......... rays.

1. A infrared
2. B ultraviolet
3. C radio
4. D red

Four photons x, y, z, k with energies 6 eV, 5 eV, 4 eV and 3 eV respectively fell one at a time on a metal surface whose work function is $E_w$, and three electrons were emitted from the surface. The work function $E_w$ of this surface is ..........

1. A $6\ eV > E_w > 5\ eV$
2. B $5\ eV > E_w > 4\ eV$
3. C $4\ eV > E_w > 3\ eV$
4. D $3\ eV > E_w$

Electromagnetic radiation of wavelength 3100 Å fell on the cathode of a photoelectric cell and photoelectrons were emitted with a maximum kinetic energy of 2.5 eV. The work function of the cathode material equals ..........

1. A 3.1 eV
2. B 2.4 eV
3. C 1.5 eV
4. D 0.9 eV

If the work function of a metal surface is $3.3125 \times 10^{-19}$ J, the threshold frequency of this metal equals ..........

1. A $4.5 \times 10^{14}$ Hz
2. B $4.8 \times 10^{14}$ Hz
3. C $5 \times 10^{14}$ Hz
4. D $5.5 \times 10^{14}$ Hz

If the work function of a metal surface is 2.48 eV, the longest wavelength of incident light that frees electrons from the surface equals ..........

1. A $4 \times 10^{-7}$ m
2. B $5 \times 10^{-7}$ m
3. C $5.5 \times 10^{-7}$ m
4. D $6 \times 10^{-7}$ m

When monochromatic light (a) of wavelength 4000 Å falls on a metal surface, electrons are emitted with a speed of $5.3 \times 10^5$ m/s. If another monochromatic light (b) of wavelength 5500 Å falls on the same metal surface, then light (b) ..........

1. A has a frequency greater than the threshold frequency of the metal
2. B has a frequency less than the threshold frequency of the metal
3. C has a frequency equal to the threshold frequency of the metal
4. D frees electrons from the metal with a greater speed

The opposite graph shows the relation between the maximum kinetic energy $(KE)_{max}$ of the electrons emitted from a metal surface and the frequency (ν) of the light falling on it. Using the graph:
(1) the threshold frequency of the metal surface equals ..........

1. A $2.4 \times 10^{14}$ Hz
2. B $2.5 \times 10^{14}$ Hz
3. C $3 \times 10^{14}$ Hz
4. D $4.8 \times 10^{14}$ Hz

The opposite graph shows the relation between the maximum kinetic energy $(KE)_{max}$ of the electrons emitted from a metal surface and the frequency (ν) of the light falling on it. Using the graph:
(2) the wavelength of the light that causes electrons to be emitted with a maximum kinetic energy of $20 \times 10^{-20}$ J equals ..........

1. A $1 \times 10^{-6}$ m
2. B $5 \times 10^{-7}$ m
3. C $1.67 \times 10^{-15}$ m
4. D $3 \times 10^{-15}$ m

In a photoelectric cell, different monochromatic light rays fell on the cathode, and the opposite graph shows the relation between the maximum kinetic energy $(KE)_{max}$ of the released electrons and the frequency (ν) of the incident light:
(1) the threshold wavelength of the cathode material equals ..........

1. A $2.07 \times 10^{-7}$ m
2. B $6.9 \times 10^{-7}$ m
3. C $2.07 \times 10^{-8}$ m
4. D $6.9 \times 10^{-8}$ m

In a photoelectric cell, different monochromatic light rays fell on the cathode, and the opposite graph shows the relation between the maximum kinetic energy $(KE)_{max}$ of the released electrons and the frequency (ν) of the incident light:
(2) the frequency of the incident light needed for an electron to be freed from the cathode surface with a maximum kinetic energy of $9.6 \times 10^{-19}$ J is ..........

1. A $1.45 \times 10^{15}$ Hz
2. B $2.9 \times 10^{15}$ Hz
3. C $5.8 \times 10^{15}$ Hz
4. D $19.2 \times 10^{15}$ Hz

The opposite figure represents the relation between the maximum kinetic energy $(KE)_{max}$ of the electrons emitted from a metal surface and the frequency (ν) of the light falling on it. If the work function of this metal surface is $5 \times 10^{-19}$ J, the value of X equals ..........

1. A $5 \times 10^{-19}$ J
2. B $1 \times 10^{-19}$ J
3. C $2 \times 10^{-19}$ J
4. D $3 \times 10^{-19}$ J

A photon of energy 3 hν fell on a metal surface whose work function is hν. The number of electrons this photon can free equals ..........

1. A zero
2. B 1
3. C 2
4. D 3

Light of frequency ν fell on a metal surface whose work function is $E_w$, and the maximum kinetic energy of the emitted electrons was KE. If the frequency of the incident light doubles, the maximum kinetic energy of the emitted electrons becomes ..........

1. A 2 KE
2. B $2\,KE - E_w$
3. C $2\,KE + E_w$
4. D $2\,KE + 2\,E_w$

If the threshold wavelength of zinc is 3000 Å, its work function equals ..........

1. A $4.42 \times 10^{-19}$ J
2. B $2.21 \times 10^{-19}$ J
3. C $3.3 \times 10^{-19}$ J
4. D $6.625 \times 10^{-19}$ J

Radiation of wavelength 3000 Å fell on a metal surface and photoelectrons were emitted with a maximum kinetic energy of 0.5 eV. If another radiation of wavelength 2000 Å falls on the same metal surface, the maximum kinetic energy of the photoelectrons becomes ..........

1. A zero
2. B less than 0.5 eV and greater than zero
3. C 0.5 eV
4. D greater than 0.5 eV

The opposite figure shows monochromatic light falling with the same intensity on two different surfaces (x, y) whose threshold frequencies are $\frac{1}{3}$ ν and $\frac{1}{2}$ ν respectively. Which of the following graphs represents the ratios of the kinetic energies of the electrons emitted from the two surfaces?

1. A A
2. B B
3. C C
4. D D

Light of frequency $6 \times 10^{14}$ Hz fell on a metal surface and the maximum kinetic energy of the emitted electrons was 0.18 eV. When light of frequency $1.6 \times 10^{15}$ Hz fell on the same metal surface, the maximum kinetic energy of the emitted electrons was 4.32 eV. The value of Planck's constant is ..........

1. A $6.626 \times 10^{-34}$ J.s
2. B $6.602 \times 10^{-34}$ J.s
3. C $6.624 \times 10^{-34}$ J.s
4. D $6.614 \times 10^{-34}$ J.s

The energy needed to free an electron from a metal surface is $3.968 \times 10^{-19}$ J. Three monochromatic light beams of wavelengths 7000 Å, 6200 Å and 5000 Å fall on the metal surface:
(1) the light beam that frees electrons is the one of wavelength ..........

1. A 7000 Å
2. B 6200 Å
3. C 5000 Å
4. D all of them

The energy needed to free an electron from a metal surface is $3.968 \times 10^{-19}$ J. Three monochromatic light beams of wavelengths 7000 Å, 6200 Å and 5000 Å fall on the metal surface:
(2) the energy of the freed electron equals ..........

1. A $1.14 \times 10^{-21}$ J
2. B $3.97 \times 10^{-21}$ J
3. C $7.94 \times 10^{-22}$ J
4. D $7 \times 10^{-22}$ J

In two different experiments on the photoelectric effect, two beams of electromagnetic rays of frequencies $4 \times 10^{15}$ Hz and $6 \times 10^{15}$ Hz fell on two surfaces of the same metal, and the ratio between the maximum kinetic energies of the released electrons in the two experiments respectively was 1 : 3. The threshold frequency of this surface is ..........

1. A $2 \times 10^{15}$ Hz
2. B $10^{15}$ Hz
3. C $3 \times 10^{15}$ Hz
4. D $4 \times 10^{15}$ Hz

The opposite table shows the radiation intensity and frequency of three spectra (A, B, C), each used separately to light a metal surface whose work function is $3.056 \times 10^{-19}$ J. Which of these spectra (A, B, C) can free the largest number of electrons per second?

1. A A
2. B B
3. C C
4. D B and C together

The opposite figure shows the photoelectric effect for a certain metal surface whose work function is $\frac{1}{2}$ hν. Which of the following figures shows a surface of the same metal?

1. A A
2. B B
3. C C
4. D D

Light fell on a metal surface whose work function is 3 eV:
(1) the lowest frequency of light that causes photoelectrons to be emitted equals ..........

1. A $4.5 \times 10^{15}$ Hz
2. B $1.21 \times 10^{15}$ Hz
3. C $7.25 \times 10^{14}$ Hz
4. D $4.5 \times 10^{14}$ Hz

Light fell on a metal surface whose work function is 3 eV:
(2) the longest wavelength of light that causes photoelectrons to be emitted is ..........

1. A $1.07 \times 10^{-7}$ m
2. B $4.14 \times 10^{-7}$ m
3. C $6.67 \times 10^{-8}$ m
4. D $1.07 \times 10^{-8}$ m

Light fell on a metal surface whose work function is 3 eV:
(3) the frequency of the light that causes photoelectrons to be emitted with a maximum kinetic energy of 2 eV is ..........

1. A $1.5 \times 10^{14}$ Hz
2. B $3.03 \times 10^{14}$ Hz
3. C $1.21 \times 10^{15}$ Hz
4. D $2.71 \times 10^{15}$ Hz

The opposite table shows the wavelengths of some colours of the visible spectrum. If these colours fall on the cathode of a photoelectric cell whose surface work function is 2.2 eV:
(1) the colours that cause photoelectrons to be emitted when they fall on the cathode are ..........

1. A red and yellow only
2. B blue and violet only
3. C violet only
4. D green, blue and violet

The opposite table shows the wavelengths of some colours of the visible spectrum. If these colours fall on the cathode of a photoelectric cell whose surface work function is 2.2 eV:
(2) the greatest speed of the emitted electrons when these colours fall on the cathode surface is ..........

1. A $445 \times 10^{3}$ m/s
2. B $13.38 \times 10^{3}$ m/s
3. C $5.64 \times 10^{5}$ m/s
4. D $5.41 \times 10^{4}$ m/s

In the following figures, electrons with the same maximum kinetic energy were emitted from the surface of each metal. Which of these metals has the largest surface work function?

1. A Metal X
2. B Metal Y
3. C Metal Z
4. D Metal M

Monochromatic light of wavelength λ fell on a metal surface and the kinetic energy of the emitted electrons was $1.6 \times 10^{-19}$ J. When another monochromatic light of wavelength $\frac{\lambda}{2}$ fell on the same surface, the kinetic energy of the emitted electrons was $6.4 \times 10^{-19}$ J. The work function of this surface equals ..........

1. A $1.2 \times 10^{-19}$ J
2. B $1.6 \times 10^{-19}$ J
3. C $2.4 \times 10^{-19}$ J
4. D $3.2 \times 10^{-19}$ J

When the frequency of the photons falling on the metal surface in a photoelectric cell increases by 20%, the kinetic energy of the electrons emitted from the metal surface increases from 0.5 eV to 0.8 eV. The work function of this metal is ..........

1. A $6.4 \times 10^{-19}$ J
2. B $4.8 \times 10^{-19}$ J
3. C $3.2 \times 10^{-19}$ J
4. D $1.6 \times 10^{-19}$ J

Compare: the radiation emitted by the Sun (a glowing body) and the radiation emitted by the Earth (a non-glowing body)
(in terms of: the region in which the wavelength of maximum radiation intensity lies).

How did Max Planck explain the fall in the intensity of radiation emitted by a glowing body at high frequencies?

Give a reason: a person can see the radiation emitted by a glowing piece of coal in a dark room, while he cannot see some of the things in the room.

An iron rod was heated gradually and different colours of the radiation it emits were seen at different temperatures. What is the dominant visible colour that appears first while heating the rod? How do you explain this?

State one application (or use) of:
(1) infrared rays.
(2) micrometre waves.
(3) the thermal radiation emitted by the human body.

The opposite figure shows a picture taken with a special type of camera. Explain what the different colour of each part shows, and what scientific idea this type of imaging depends on.

The opposite diagram shows the structure of a cathode ray tube:
(1) Which part are the electrons emitted from? What condition is needed for their emission?
(2) How does part (2) control the brightness of the fluorescent screen from one point to another?
(3) State two functions that part (3) performs for the electron beam.
(4) What factor controls the speed of the electrons when they reach part (3)?
(5) Why is the tube evacuated of air?

The opposite figure shows a diagram of a cathode ray tube working perfectly. What happens to the cathode rays inside the tube when:
(1) the X plates stop working?
(2) the Y plates stop working?

The opposite figure represents a photoelectric cell:
(1) Explain why the anode is made of a thin wire.
(2) Which property of the incident light can be increased to increase the ammeter reading?
(3) What are the factors that affect each of:
(a) the work function of the metal surface?
(b) the maximum kinetic energy of the electrons emitted from the cathode?

Explain: electrons may not be emitted from a metal surface even though it is exposed to a certain electromagnetic radiation for a long time.

Explain why, when very bright red light falls on a caesium surface, no photoelectrons are emitted, while when dim blue light falls on it, photoelectrons are emitted from the surface.

Compare: the cathode ray tube and the photoelectric cell (in terms of: the type of energy that frees the electrons from the cathode).

If the work function of copper is 4.4 eV, can visible light free electrons when it is shone on a copper surface? Explain your answer.

Write the mathematical relation shown by the graph and what the slope of the straight line equals for each of the following:
where: (υ) is the frequency, (E) the photon energy, (λ) the photon wavelength.

A scientist plotted the values he got in an experiment on the photoelectric effect for a metal, as in the opposite graph. Find:
(1) Planck's constant.
(2) the threshold frequency of the metal.

The opposite graph shows the relation between the maximum kinetic energy of the electrons emitted from the surfaces of three metals (x , y , z) and the frequency of the light falling on each. Using the graph:
(1) Calculate the work function of metal y.
(2) What is the lowest frequency of electromagnetic radiation needed to free an electron from any of these metals?
(3) If light of a certain frequency falls so that it frees electrons from the surface of each of the three metals, which metal releases electrons with the greatest kinetic energy? Explain your answer.

Light of frequency υ₁ fell on the surface of metal x whose work function is (Ew)x, and photoelectrons were emitted with a maximum kinetic energy (KE)₁. Another light of frequency υ₂ fell on the surface of metal y whose work function is (Ew)y, and photoelectrons were emitted with a maximum kinetic energy (KE)₂. Given that (Ew)y < (Ew)x and (KE)₂ = (KE)₁, which light has the higher frequency? Explain your answer.

The opposite figure shows a glowing black body placed midway between two metal surfaces (x , y). The work function of metal (x) is twice that of metal (y), and electrons were emitted from both surfaces. From which surface are electrons emitted at a greater rate? Why?

Which of the following graphs shows the relation between the photon energy (E) in black body radiation and its wavelength (λ)? (1st session 2023)

1. A A
2. B B
3. C C
4. D D

The opposite figure represents Planck's curve for the radiation emitted by a hot body. If the body is left to cool, the curve can be represented by figure .......... (2nd session 2023)
(Note: the figures are not drawn to scale)

1. A A
2. B B
3. C C
4. D D

The opposite graph shows Planck's curve for the radiation of a hot body at 6000 K, and the wavelength at maximum radiation intensity emitted by the body is λ₀. For the wavelength at maximum radiation intensity to become (2λ₀), .......... (2nd session 2024)

1. A the temperature must be lowered by 1500 K
2. B the temperature must be raised by 3000 K
3. C the temperature must be lowered by 3000 K
4. D the temperature must be raised by 1500 K

The opposite graph shows the relation between the wavelength (λ) at maximum radiation intensity emitted by a hot body and the reciprocal of the temperature (1/T) on the kelvin scale. The wavelength at maximum radiation intensity emitted by the body at 2000 K equals .......... (1st session 2024)

1. A $15000\ \text{\AA}$
2. B $20000\ \text{\AA}$
3. C $15000\ nm$
4. D $20000\ nm$

A laser is emitted with a wavelength of 200 nm. How many emitted laser photons have a total energy of 1 joule? (Sample exam 2025)

1. A $8.32 \times 10^{18}$
2. B $1.01 \times 10^{18}$
3. C $1.36 \times 10^{18}$
4. D $9.95 \times 10^{19}$

The graph represents the relation between the intensity of electromagnetic radiation (I) and the wavelength (λ) of the radiation emitted by three glowing bodies (X), (Y), (Z). Which of the following statements is correct? (1st session 2025)

1. A Body (X) has the highest temperature of the three bodies
2. B Body (Y) has the highest temperature of the three bodies
3. C Body (Z) has the highest temperature of the three bodies
4. D The three bodies have the same temperature

The opposite graph represents Planck's curve for solar radiation. The radiation of wavelength λ₂ may be .......... rays, and the energy of one of its photons is .......... the energy of a photon of the radiation of wavelength λ₁ (2nd session 2025)

1. A ultraviolet , equal to
2. B ultraviolet , greater than
3. C infrared , less than
4. D infrared , equal to

The graph represents the relation between the intensity of electromagnetic radiation (I) and the wavelength (λ) of the radiation emitted by three glowing bodies. The ratio between the wavelengths at maximum radiation intensity $(\lambda_Z : \lambda_Y : \lambda_X)$ is .......... (Sample exam 2026)

1. A $4 : 5 : 6$
2. B $6 : 5 : 4$
3. C $5 : 10 : 12$
4. D $15 : 12 : 10$

Two glowing bodies (X) and (Y) of the same material and the same surface area, at temperatures 2000 K and 6000 K respectively, each emit electromagnetic radiation. If the frequencies at which their maximum radiation intensity occurs are $\upsilon_X$ and $\upsilon_Y$ respectively, the ratio $\frac{\upsilon_X}{\upsilon_Y}$ equals .......... (Sample exam 2026)

1. A $\frac{1}{3}$
2. B $\frac{3}{1}$
3. C $\frac{3}{4}$
4. D $\frac{4}{3}$

In the opposite figure, when one of the wavelengths of green light falls on a caesium surface, electrons are only just freed from it. In which of the following figures are electrons freed from the caesium surface with kinetic energy? (Trial exam / June 2021)

1. A A
2. B B
3. C C
4. D D

The opposite graph shows the relation between the maximum kinetic energy of the electrons emitted from the photoelectric cell and the frequency of the light falling on the cathode. Which of the following wavelengths frees electrons with a kinetic energy of $6.6 \times 10^{-20}\ J$? (Trial exam / June 2021)

1. A $5.5 \times 10^{-7}\ m$
2. B $5.3 \times 10^{-7}\ m$
3. C $5.6 \times 10^{-7}\ m$
4. D $5.7 \times 10^{-7}\ m$

The opposite graph represents the relation between the maximum kinetic energy of the electrons released from a metal surface and the frequency of the light falling on it. The unit of the value of point (2) divided by the value of point (1) is .......... (1st session 2021)

1. A $kg.m^2.s$
2. B $J/s$
3. C $kg.m^2.s^{-1}$
4. D $kg.m.s^{-1}$

The opposite graph represents the relation between the maximum kinetic energy of the electrons emitted from the cathode surface of a photoelectric cell and the frequency of the incident light. The work function of the surface is .......... (1st session 2021)

1. A 2.7 eV
2. B 0.27 eV
3. C 0.027 eV
4. D 27 eV

The opposite figure shows the relation between the photoelectric current and the intensity of the light falling on the cathode of three photoelectric cells of different metals (X, Y, Z). Which metal has a threshold frequency greater than the frequency of the incident light? (2nd session 2021)

1. A Metal (X)
2. B Metal (Y)
3. C Metal (Z)
4. D All the metals

The graph represents the relation between the kinetic energy of the electrons released from the surfaces of four metals (A, B, C, D) and the frequency of the light falling on each. Which frequency allows electrons to be emitted from the surfaces of metals (A, B) only and not from the surfaces of metals (C, D)? (1st session 2022)

1. A $\upsilon_3$
2. B $\upsilon_5$
3. C $\upsilon_2$
4. D $\upsilon_4$

The figure shows a metal surface X whose threshold frequency is $\upsilon_c$. A photon of frequency $(\upsilon_1 = 2\upsilon_c)$ fell on it and the electron was freed with a maximum kinetic energy $(KE)_1$. When the photon was replaced by another of frequency $(\upsilon_2 = 4\upsilon_c)$, the electron was freed with a maximum kinetic energy $(KE)_2$. The ratio $\frac{(KE)_1}{(KE)_2}$ = .......... (1st session 2022)

1. A $\frac{1}{2}$
2. B $\frac{1}{3}$
3. C $\frac{1}{4}$
4. D $\frac{1}{8}$

A metal surface has a work function $(E_w)$. A photon of energy $(E_1)$, equal to three times the work function, fell on it and the electron was freed with speed (v). When the first photon is replaced by another of energy $(E_2)$, equal to seven times the work function, the electron will be freed with speed .......... (2nd session 2022)

1. A $\sqrt{3}\ v$
2. B $3\ v$
3. C $\sqrt{6}\ v$
4. D $6\ v$

Given that the electron mass = $9.1 \times 10^{-31}\ kg$, the electron charge = $1.6 \times 10^{-19}\ C$, Planck's constant = $6.625 \times 10^{-34}\ J.s$ and the speed of light in vacuum = $3 \times 10^{8}\ m/s$, and using the data on the drawing, the maximum speed of the electron emitted when a UV photon falls on a thorium surface equals .......... (2nd session 2022)

1. A $7.43 \times 10^{4}\ m/s$
2. B $7.43 \times 10^{6}\ m/s$
3. C $7.43 \times 10^{5}\ m/s$
4. D $7.43 \times 10^{3}\ m/s$

Electromagnetic radiation fell on three surfaces of different metals A, B, C, and photoelectrons were freed from each surface. If the order of the work functions of these metals is $(E_w)_C > (E_w)_B > (E_w)_A$, which of the following choices gives the correct order of the maximum kinetic energy of the photoelectrons? (Trial exam 2023)

1. A $(KE)_B < (KE)_A < (KE)_C$
2. B $(KE)_C < (KE)_B < (KE)_A$
3. C $(KE)_A < (KE)_C < (KE)_B$
4. D $(KE)_C < (KE)_A < (KE)_B$

When the grid potential in a cathode ray tube is changed from (−12 V) to (−4 V) while the potential difference between the anode and the cathode stays constant, which of the following choices is correct? (1st session 2024)

1. A rate of electrons passing through the grid: decreases , screen brightness: increases
2. B rate of electrons passing through the grid: increases , screen brightness: increases
3. C rate of electrons passing through the grid: decreases , screen brightness: decreases
4. D rate of electrons passing through the grid: increases , screen brightness: decreases

When photons of light of frequency (υ) fell at a rate $\phi_L$ on the cathode of a photoelectric cell, the photoelectric current produced was 3 mA. When the rate at which photons of the same light fall on the cathode is doubled, .......... (1st session 2024)

1. A current: 3 mA , work function: stays the same
2. B current: 3 mA , work function: becomes half
3. C current: 6 mA , work function: stays the same
4. D current: 9 mA , work function: doubles

If the potential difference used between the anode and the cathode in a cathode ray tube is 500 V, the maximum kinetic energy of the electrons emitted from the cathode equals .......... (Sample exam 2025)

1. A $4 \times 10^{-17}\ J$
2. B $8 \times 10^{-17}\ J$
3. C $12 \times 10^{-17}\ J$
4. D $16 \times 10^{-17}\ J$

The opposite figure represents a diagram of the binding energy of the electrons in a metal surface. The work function of the metal surface equals .......... (Sample exam 2025)

1. A 2.5 eV
2. B 3 eV
3. C 3.5 eV
4. D 4 eV

Photoelectrons are emitted from a metal surface when a certain light falls on it. What happens to the work function and to the maximum kinetic energy of the emitted electrons when another light of higher frequency falls on the metal? (Trial exam 2023)

Monochromatic light of frequency $6 \times 10^{14}\ Hz$ fell on the cathode of a photoelectric cell and electrons were emitted with a maximum kinetic energy of 1 eV. When another light of frequency (X) hertz fell on the same cathode, the maximum kinetic energy of the emitted electrons was 0.38 eV. Calculate the frequency of light (X). (1st session 2023)

The figure shows the photoelectric effect in two cases (X, Y). In case (X), dim blue light falls on the metal surface, and in case (Y), high-intensity red light falls on the same metal surface. Assuming electrons are emitted from the metal surface in both cases, compare the photoelectrons emitted in the two cases (in terms of: their maximum speed - their rate of emission). (1st session 2025)

The figure shows a photoelectric cell circuit on which a beam of monochromatic light falls. The ammeter reads a weak photoelectric current in the circuit. To increase the photoelectric current in the circuit, what must be done about: (2nd session 2025)
(1) the way the battery is connected in the circuit?
(2) the properties of the light falling on the cell?