1.1. State what is meant by a photon.

1.2. Electromagnetic radiation of a varying frequency f and constant intensity I is used to illuminate a metal surface. At certain frequencies, electrons are emitted from the surface of the metal.  

(i)

State the name of this phenomenon.

[1] 

(ii)

The variation with f of the maximum kinetic energy E_MAX of the emitted electrons is shown in Fig. 1.1.

Fig. 1.1

Describe four conclusions that can be drawn from the graph in Fig. 1.1. The conclusions may be qualitative or quantitative.  

[1]

1.3. The experiment in (b) is carried out twice more. Each time one change is made to the method used. 

State, and explain, how the graph obtained would compare with Fig. 1.1. when: 

(i)

the same metal is used, but with electromagnetic radiation of intensity $\frac{I}{2}$

[2]

(ii)

a different metal is used, but the intensity I of the radiation is the same.

[2]