(a) Explain what is meant by photoelectric emission

(b) Draw a labelled diagram showing the structure of a simple type of a photocell and explain its mode of operation.

(c) State four applications of photoelectric emission.

(d) In a photocell, no electrons are emitted until the threshold frequency of light is reached. Explain what happens to the energy of the light before emission of electrons begins. State one factor that may affect the number of emitted electrons.