Questions on Photoelectric Effect
20 Multiple-Choice Questions: Photoelectric Effect
1. What is the photoelectric effect?
A) The absorption of heat by a metal
B) The emission of electrons from a metal surface when light shines on it
C) The formation of an electric arc in a vacuum
D) The reflection of light from polished surfaces
E) The splitting of white light into its spectrum
2. Which scientist is most closely associated with explaining the photoelectric effect?
A) Isaac Newton
B) Max Planck
C) Niels Bohr
D) Albert Einstein
E) James Clerk Maxwell
3. In the photoelectric effect, the electrons that are emitted are called:
A) Protons
B) Neutrons
C) Valence electrons
D) Photons
E) Photoelectrons
4. Which quantity determines whether electrons will be ejected in the photoelectric effect?
A) The temperature of the metal
B) The frequency of the light
C) The brightness of the light
D) The surface area of the metal
E) The atomic mass of the metal
5. What is the minimum energy needed to eject an electron from a metal surface called?
A) Potential energy
B) Kinetic energy
C) Photon energy
D) Work function
E) Electric field strength
6. According to Einstein, light is made of:
A) Continuous waves
B) Gamma rays
C) Particles called photons
D) Electron streams
E) Sound pulses
7. What happens if the frequency of light is below the threshold frequency of the metal?
A) Electrons are emitted more rapidly
B) The metal glows red
C) No electrons are emitted
D) The photoelectrons become faster
E) The energy is stored in the metal
8. The kinetic energy of photoelectrons depends on:
A) The wavelength of light
B) The angle of incidence
C) The color of the metal
D) The intensity of light
E) The frequency of light above the threshold
9. Increasing the intensity of light above the threshold frequency causes:
A) Faster electrons
B) More electrons to be emitted
C) Lower work function
D) Change in threshold frequency
E) No change
10. Which equation describes the photoelectric effect?
A) E = mc²
B) F = ma
C) E = hf – φ
D) p = mv
E) V = IR
11. In the equation E = hf – φ, what does φ represent?
A) The electric field
B) The speed of light
C) The threshold frequency
D) The work function
E) The momentum
12. What is the unit of Planck’s constant (h)?
A) kg·m/s²
B) N·m
C) J·s
D) Hz
E) m/s
13. Which metal was used in many early photoelectric experiments?
A) Copper
B) Silver
C) Sodium
D) Uranium
E) Lead
14. What does the term “threshold frequency” refer to?
A) The frequency below which light reflects
B) The frequency at which electrons are fastest
C) The minimum frequency to eject electrons
D) The maximum frequency emitted by a source
E) The frequency of gamma rays
15. The photoelectric effect provides evidence that:
A) Light is purely a wave
B) Light has no mass
C) Light can behave as a particle
D) Electrons have color
E) Energy is continuous
16. If light intensity is increased but frequency stays below threshold, what happens?
A) Electrons gain energy
B) Electrons are emitted in greater numbers
C) Electrons move faster
D) No electrons are emitted
E) The work function decreases
17. Why couldn’t classical wave theory explain the photoelectric effect?
A) It predicted no emission of light
B) It suggested energy is absorbed continuously
C) It ignored the metal’s temperature
D) It accounted for photon collisions
E) It used incorrect formulas
18. What happens to excess energy when a photon hits a metal surface with more energy than the work function?
A) It disappears
B) It increases the metal’s mass
C) It becomes the kinetic energy of the ejected electron
D) It is stored in the metal
E) It reduces the speed of light
19. Which application is based on the photoelectric effect?
A) Solar panels
B) Nuclear reactors
C) MRI machines
D) Hydraulic brakes
E) Sound amplifiers
20. Which of the following increases the number of photoelectrons emitted?
A) Decreasing frequency
B) Lowering temperature
C) Increasing light intensity
D) Decreasing the work function
E) Increasing Planck’s constant
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Answers with Extended Explanations
1. B – The photoelectric effect is the emission of electrons when light hits a material.
2. D – Einstein explained it using the photon model of light and won the Nobel Prize for it.
3. E – The emitted electrons are called photoelectrons.
4. B – Frequency must be high enough to eject electrons.
5. D – The work function is the minimum energy needed to eject an electron.
6. C – Einstein proposed light is made of photons, which are energy packets.
7. C – If the frequency is too low, no electrons are ejected regardless of intensity.
8. E – The excess energy from higher frequency becomes kinetic energy.
9. B – Higher intensity (at sufficient frequency) means more photons, so more electrons.
10. C – Einstein's equation for the photoelectric effect: Ek=hf−ϕE_k = hf - \phiEk=hf−ϕ.
11. D – φ is the work function, the energy needed to eject an electron.
12. C – Planck’s constant has units of Joule·second (J·s).
13. C – Sodium was commonly used due to its low work function.
14. C – Threshold frequency is the minimum frequency to cause electron emission.
15. C – The effect supports the particle nature of light.
16. D – Below threshold, no electrons are emitted, no matter how intense.
17. B – Classical theory predicted gradual energy absorption, not the observed instant ejection.
18. C – Extra energy becomes the kinetic energy of the electron.
19. A – Solar panels use the photoelectric effect to convert light into electricity.
20. C – More intensity means more photons, so more photoelectrons.
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