(a)(i) Explain photoelectric emission.

(ii) State four applications of photoelectric emission.

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

(c) In a photocell, no electrons are emitted until the threshold frequency of light is reached.

(i) Explain what happens to the energy of the light before emission of electrons begin.

(ii) State one factor that may affect the number of emitted electrons.