4.5 Quantum Physics

4.5.1 Photons

Learners should be able to demonstrate and apply their knowledge and understanding of:

(a) the particulate nature (photon model) of electromagnetic radiation

(b) photon as a quantum of energy of electromagnetic radiation

(c) energy of a photon;

(d) the electronvolt (eV) as a unit of energy

(e) (i) using LEDs and the equation  to estimate the value of Planck constant h

(ii) Determine the Planck constant using different coloured LEDs.

4.5.2  The photo-electric effect

Learners should be able to demonstrate and apply their knowledge and understanding of:

(a) (i) photoelectric effect, including a simple experiment to demonstrate this effect

Learners should understand that the photoelectric effect provides evidence for particulate nature of electromagnetic radiation.

Remember how Young's slits proved that light is a wave.  This is the experiment that proves that it is made of particles i.e. photons.

(ii) demonstration of the photoelectric effect using, e.g. gold-leaf electroscope and zinc plate

(b) a one-to-one interaction between a photon and a surface electron

You should say this in every answer to a photo-electric effect question.  It always gets a mark.

(c) Einstein’s photoelectric equation

(d) work function; threshold frequency

(e) the idea that the maximum kinetic energy of the photoelectrons is independent of the intensity of the incident radiation

(f) the idea that rate of emission of photoelectrons above the threshold frequency is directly proportional to the intensity of the incident radiation.

4.5.3  Wave-particle duality

Learners should be able to demonstrate and apply their knowledge and understanding of:

(a) electron diffraction, including experimental evidence of this effect

Learners should understand that electron diffraction provides evidence for wave-like behaviour of particles.

This is the third important experiment that proves that given that light is a particle and a wave then all particles must be waves.

(b) diffraction of electrons travelling through a thin slice of polycrystalline graphite by the atoms of graphite and the spacing between the atoms

(c) the de Broglie equation