(a)[2]
State the meaning of the term photon.
(b)[3]
Calculate the energy, in eV, for a photon of light with wavelength $540\,\text{nm}$.
(c)[4]
The outermost electron energy bands of a semiconductor material are shown in Fig. 11.1. The width of the forbidden band is $1.1\,\text{eV}$. Explain why, when photons of light, each of energy $2.1\,\text{eV}$, strike the semiconductor material, its resistance decreases.