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 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
  • D. h

4. What is equal to the Y intercept of this graph?

  • A. hf
  • B. -Φ
  • C. Φ
  • D. h
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. The kinetic energy of the photoelectrons can be found by applying a stopping potential.
If the work function of the metal is 2.8 eV, and the value of 'hf' is 5.7 eV, then the stopping potential is:

  • A. 2.9 eV
  • B. 2.9 V
  • C. 8.5 eV
  • D. 8.5 V
10. A red 60W lamp is used to produce a small current I from a photocell, with a stopping potential of V. The red lamp is replaced with a violet lamp of the same power output. What effect does this have on I and V?  
I V
A
 decreases decreases
B
 no effect decreases
C
 decreases increases
D
 no effect increases