When red light is incident on the metallic surface M the microammeter registers a current. Explain how a current is established in this circuit even though nothing joins M to C inside the tube.

The graph shows the variation with voltage V of the current I in the circuit.

The work function of the metallic surface M is 0.48 eV.

(i) Define work function.

(ii) State the maximum kinetic energy of an electron immediately after it has been emitted from M.

(iii) Calculate the energy of a photon incident on M.

(iv) The red light incident on M is now replaced by blue light. The number of photons incident on M per second is the same as in (b).

On the axes opposite, sketch a graph to show the variation with V of the current I.

the light causes emission of (photo)electrons;
which move (from M) to C;

(i) the (minimum) energy required to eject an electron from the metal;

(ii) 1.42 eV;
Allow answer in Joules.

(iii) (1.42+0.48 )=1.90 eV;
Allow answer in Joules.

(iv) line starting to the left of where red curve starts;
and saturates at the same value as red;