The photoelectric effectEdexcel International A Level Physics: Subtopic test

1. 1
   A student shines ultraviolet light on to a clean zinc plate connected to a sensitive charge detector and finds that electrons are emitted from the plate. When she replaces the ultraviolet lamp with a very bright red lamp, no electrons are emitted, however bright the lamp is made.

   (a)

   What is meant by the work function of a metal?

   [1 mark]

   • AThe minimum energy needed to remove an electron from the surface of the metal
   • BThe maximum kinetic energy of an emitted photoelectron
   • CThe total energy of all the electrons in the metal
   • DThe energy gained by an electron for each photon absorbed

   (b)

   The intensity of the ultraviolet light is doubled, with the frequency unchanged. Which statement is correct?

   [1 mark]

   • AThe maximum kinetic energy doubles and the number of electrons emitted per second is unchanged
   • BThe number of electrons emitted per second doubles and the maximum kinetic energy is unchanged
   • CBoth the maximum kinetic energy and the number of electrons emitted per second double
   • DNeither the maximum kinetic energy nor the number of electrons emitted per second changes

   (c)

   Explain why no electrons are emitted by the bright red lamp.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A clean sodium surface has a work function of 2.3 eV. It is illuminated with light of wavelength 400 nm. Use the Planck constant h = 6.63 × 10⁻³⁴ J s, the speed of light c = 3.00 × 10⁸ m s⁻¹ and 1 eV = 1.60 × 10⁻¹⁹ J.

   (a)

   What is the work function of sodium in joules?

   [1 mark]

   • A1.4 × 10¹⁹ J
   • B1.6 × 10⁻¹⁹ J
   • C3.7 × 10⁻¹⁹ J
   • D7.0 × 10⁻²⁰ J

   (b)

   What is the threshold frequency of sodium?

   [1 mark]

   • A1.8 × 10⁻¹⁵ Hz
   • B3.5 × 10³³ Hz
   • C1.4 × 10¹⁹ Hz
   • D5.6 × 10¹⁴ Hz

   (c)

   Calculate the maximum kinetic energy of the photoelectrons emitted by the 400 nm light.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A metal Q has a work function of 3.6 × 10⁻¹⁹ J. It is illuminated with light of frequency 6.0 × 10¹⁴ Hz. Use the Planck constant h = 6.63 × 10⁻³⁴ J s and the electron mass m = 9.11 × 10⁻³¹ kg.

   (a)

   Calculate the maximum kinetic energy of the photoelectrons.

   [3 marks]

   (b)

   Calculate the threshold frequency of metal Q and the maximum speed of the photoelectrons.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A class investigates the photoelectric effect using a clean metal plate and a lamp whose frequency can be varied. They measure the maximum kinetic energy of the emitted photoelectrons. Take 1 eV = 1.60 × 10⁻¹⁹ J.

   (a)

   Explain how the observations of the photoelectric effect provide evidence for the particle nature of electromagnetic radiation, and why the wave model cannot explain them.

   [6 marks]

   (b)

   The maximum kinetic energy was 1.64 × 10⁻¹⁹ J for light of frequency 7.0 × 10¹⁴ Hz and 2.97 × 10⁻¹⁹ J for light of frequency 9.0 × 10¹⁴ Hz. Use these data to determine the Planck constant, the work function of the metal in eV and its threshold frequency.

   [6 marks]

   Total for question 4: 12 marks

End of questions