(a)[1]
State what the meaning of diffraction is.
(b(i))[2]
Light with wavelength $720\,\text{nm}$ in a vacuum falls normally on a diffraction grating, as shown in Fig. 6.1. Calculate the frequency of the light.
(b(ii))[3]
Calculate how many lines there are per unit length in the diffraction grating.
(b(iii))[2]
The light in Fig. 6.1 is now replaced by light of another wavelength $\lambda$. It is found that the third-order maxima for this light occur at the same positions as the second-order maxima of the light in Fig. 6.1. Calculate, in $\text{nm}$, the wavelength $\lambda$.