Quantum Physics - CAIE

Define the photon

A quantum of energy of electromagnetic radiation

What is the photoelectric Effect [2 marks]

• Emission of electron

• When EM radiation is incident (on surface)

Define the work function

The minimum energy needed by an electron to free itself from the surface of a metal. Work function is a property of the metal.

Define the De Broglie Wavelength

The wavelength associated with a moving particle

Explain why the maximum kinetic energy of the electron emitted from a metal surface is independent of the intensity of the incident electromagnetic radiation. [3 marks]

• The frequency of a photon determines its energy.

• The intensity of light determines the number of photons per unit time.

• The intensity of light does not determine the energy of a photon.

• The kinetic energy of an electron depends on the energy of one photon.

What is the equation linking momentum of a photon and its energy?

p = E/c, where c = speed of light in a vacuum.

Explain how the emission spectrum provides evidence for the existence of discrete energy levels for electrons in an atom [3 marks].

• Energy of photon has a corresponding frequency

• change in electron energy level emits a single photon

• photon energy = difference in energy levels

• discrete frequencies must have come from discrete energy gaps.

• discrete energy changes imply discrete energy levels.