State the meaning of a photon.
Electromagnetic radiation with frequency $f$ that varies and constant intensity $I$ is directed at a metal surface. At some frequencies, electrons are released from the metal. Figure 7.1 shows how the maximum kinetic energy $E_{\text{MAX}}$ of the emitted electrons changes with $f$.
State the name given to this effect.
Describe three conclusions that can be made from the graph in Fig. 7.1. Your conclusions may be qualitative or quantitative.
The experiment in (b) is repeated twice, and one change is made each time. State, with a reason, how the graph obtained would compare with Fig. 7.1 when:
a different metal is chosen, while the intensity $I$ of the radiation is kept unchanged.
the same metal is used, but the electromagnetic radiation has intensity $2I$.