# Photoelectric effect – problems and solutions

1. The correct statement about the photoelectric effect is …

A. Can be explained by considering light as a wave

B. Electrons released by the metal surface will decrease if the light frequency increased

C. The intensity of light does not affect the energy of electrons coming out of the metal surface

D. The photoelectric effect occurs in the infrared region

E. The photoelectric effect will occur when the light intensity of the metal is large

Solution

A. The photoelectric effect can be explained by considering light as a particle, not as a wave. Light energy is not distributed continuously as the waves move but are small packets called photons aka light quanta (just imagine it like rainwater).

B. If the frequency of light increased then the electron coming out of the metal surface increases. When the frequency of light increased the energy of light increases. The larger the energy absorbed the more electrons coming out of the metal surface.

C. The intensity of light corresponds to the speed of the emission of energy or the rapidity of light energy on the metal surface. The intensity of light enlarged does not mean that the energy of light is enlarged. The photon energy (E = hf) depends on the frequency (f) or wavelength and Planck’s constant (h).

D. Photoelectric effect occurs at the frequency or wavelength of ultraviolet light aka ultraviolet rays. The ultraviolet frequency is the threshold frequency at which the photon energy is capable of releasing electrons from the metal surface. The infrared frequency cannot be because it is too small, otherwise, the frequency of x-rays and gamma rays can be due to greater frequency than ultraviolet.

E. The intensity of the light does not affect the photoelectric effect

2.
(1) The photoelectric effect can be explained by assuming light consists of energy packets
(2) The photoelectric effect can prove that light can behave as a wave
(3) The electron energy coming out of the metal surface depends on the frequency
(4) The photoelectric effect occurs in the vicinity of the infrared region
The true statement about the photoelectric effect is…

A. (1) and (2)

B. (1) and (3)

C. (1) and (4)

D. (2) and (3)

E. (2) and (4)

Solution

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3.

(1) The detachment of electrons from the metal is determined by the wavelength of the incoming light
(2) The intensity of the incoming light does not guarantee the removal of electrons from the metal surface

(3) Below threshold frequency, the electrons remain out of the metal as the intensity of the incoming light is magnified

The correct statement relating to the photoelectric effect is…..

Solution
Statement (1): This statement is true. If the wavelength that comes is smaller than the wavelength of the metal threshold then the electrons are not released.

Statement (2): This statement is true. The exit of electrons from the metal surface depends on the frequency or wavelength or light energy.

Statement (3): This statement is false. Electrons out of metal if the light frequency is greater than the metal threshold frequency. The absence of electrons from the metal surface depends on the energy of light rather than on the intensity of light. Light energy depends on frequency or wavelength (E = hf). The intensity of light is related to the rate of light energy emitting.

4.

(1) Electrons can exit from metal surfaces when metal is radiated the electromagnetic waves

(2) The detachment of electrons from the metal surface depends on the frequency of incoming light

(3) The work function for each metal is the same

The correct statement relating to the photoelectric effect is…..

Solution

Statement (1): This statement is true. Electromagnetic waves consist of many types of waves that have different frequencies or wavelengths. Only electromagnetic waves that have a frequency or wavelength greater than the threshold or wavelength frequency can remove electrons from the metal.

Statement (2): This statement is true. If the light frequency is smaller than the metal threshold frequency then the electron is inseparable from the metal. Conversely, if the frequency of light is greater than the metal threshold frequency, the electron is released from the metal.

Statement (3): This statement is false. The metal work function is the minimum work or minimum energy required to remove electrons from the metal surface. The work function for each metal depends on the characteristics of the metal.

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5.

(1) The electrons radiated in the photoelectric effect are called photon electrons

(2) The radiated electron rate does not depend on the intensity of light that concerns the metal surface

(3) The kinetic energy of the emitted electrons depends on the energy of the light waves on the metal surface

(4) To remove electrons from a metal surface independent of threshold frequency (fo)
The true statement about the photoelectric effect is…..

Solution
(1) Electrons that are radiated are called photoelectrons

(2) The radiated electron rate corresponds to the number or number of electrons emitted over a period of time. The rate of emitted electrons is influenced by the intensity of light, where the intensity of light is related to the rate of light transmission. The intensity of light affects only when the energy of light is greater than the energy of the metallic threshold. If the light energy is smaller than the threshold energy of the metal, the light intensity has no effect.

(3) This statement is true. The kinetic energy of the emitted electrons depends on the energy of the light waves on the metal surface. The electron is released from the surface of the metal only when the light energy is greater than the threshold energy of the metal.

(4) This statement is false. If the frequency of the incoming light wave is smaller than the metallic threshold frequency, the electrons are not released. So the discharge of electrons depends on the threshold frequency.

6.
(1) the frequency of light illuminating the cathode must be greater than the threshold frequency
(2) the working function of the cathode metal is greater than the energy of light which illuminates the cathode
(3) the threshold wavelength must be greater than the wavelength of the light shining on the cathode
(4) the kinetic energy of electrons released from the cathode must be greater than the threshold energy
In order for photoelectrons to be met:

Solution
(1) This statement is true. Photoelectric happens when the frequency of light illuminating the cathode metal, is greater than the threshold frequency of the cathode metal.

(2) This statement is false. The work function is minimum work or minimum energy required to release electrons. In order for photoelectric to occur the light energy must be greater than the working function of the cathode metal.

(3) This statement is false. Photoelectric happens when the wavelength of light illuminates the cathode, greater than the threshold wavelength of the cathode metal.

(4) This statement is true. In order to escape the metal, the kinetic energy of the electron must be greater than the threshold energy of the cathode metal.

The correct answers are (1) and (4).

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7. Notice the following statement:

(1) The working function of the metal must be less than the light energy illuminating the cathode metal

(2) The energy of the cathode threshold is greater than the light energy illuminating the cathode metal

(3) The kinetic energy of electrons released from the cathode is always greater than the energy of the cathode threshold

(4) The kinetic energy of electrons released from the cathode surface is proportional to the energy of light which illuminates the cathode

The exact statement on the photoelectric effect is…..

Solution
(1) This statement is true

(2) This statement is false

(3) This statement is true

(4) This statement is true only if the energy of light shining on the cathode is greater than the threshold energy of the cathode metal. If the light energy is smaller than the threshold energy of the metal then the electrons cannot be separated from the surface of the cathode metal.

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