10 minutes maximum! Can you do it in 5?

1. The photoelectric effect demonstrates..

  • A. The wave properties of photons and electrons.
  • B. The particle properties of photons and the wave properties of electrons.
  • C. The wave properties of photons and the particle properties of electrons.
  • D. The particle properties of photons and electrons.

2. The work function Φ of a metal is defined as:

  • A. The frequency of a photon required to liberate an electron from the metal.
  • B. The minimum energy required to liberate an electron from the metal.
  • C. The momentum given to an electron liberated from the metal.
  • D. The kinetic energy given to an electron liberated from the metal.

3-5. The graph below shows how the maximum kinetic energy Emax of the electrons varies with the frequency of the incident light on a clean metal surface.

photoelectric effect KE

  

3. What is the gradient of this graph?

  • A. hf
  • B. Φ
  • C. Φ-hf
  • D. h

4. What is the Y intercept of this graph?

  • A. hf
  • B. -Φ
  • C. Φ
  • D. - hf
5. Which of the following quantities is equal to the threshold frequency?  

 

6. Light of wavelength λ is incident on a clean metal sheet, and photoelectrons are liberated with minimal kinetic energy. Which of the following will changes will prevent photoelectrons from being emitted?

  • A. Increase the energy of the incident photons
  • B. Increase the wavelength of the incident light.
  • C. Use a metal sheet with a lower work function.
  • D. Decrease the power output of the light source.

7. Photoelectrons of maximum kinetic energy E are liberated from a metal sheet of work function Φ when photons of frequency f are incident on the metal.
What is the maximum kinetic energy of the photoelectrons if a new metal of work function 2Φ is used, and the frequency of light is also doubled?

  • A. ½E
  • B. E
  • C. 2E
  • D. 4E

8. Photoelectrons liberated from a metal can produce a current I in an external circuit. The number of photons incident on the sheet is kept constant whilst the frequency f is varied. Which of the following graphs best shows how I varies with f?

  

9. Which of these observations of the photoelectric effect cannot be explained with a wave model of light?

I. Light below the threshold frequency cannot dislodge electrons, regardless of intensity
II. Light of higher intensity increases the total energy of electrons released
III. Light of higher intensity has no effect on the maximum kinetic energy of each electron released
  • A. I and III
  • B. II and III
  • C. I only
  • D. II only

10. A student investigates the photoelectric effect on a metal with a fixed work function, using a 60W red light source. They measured the kinetic energy of electons released (Ek) as well as the number of electrons released per second, N.

How will these values change if a 60W blue light source is used instead?

  
Kinetic energy of electrons in blue light number of electrons per second in blue light
A
 < Ek < N
B
 < Ek > N
C
 > Ek < N
D
 > Ek > N