(a(i))[1]
Explain the meaning of coherence.
(a(ii))[1]
Explain the meaning of interference.
(b(i))[2]
Find the wavelength of the light. Bright spots are observed on a screen placed parallel to the grating. The angle for each second order maximum is $51^{\circ}$. The number of lines per unit length on the diffraction grating is $6.7 \times 10^5\,\text{m}^{-1}$.
(b(ii))[1]
State and explain how, if at all, the distance between the second order maximum spots on the screen changes when the light from the laser is replaced by light of a shorter wavelength.