A laser is used to create an interference pattern on a screen, as illustrated in Fig. 6.1. The laser emits light with wavelength $630\,\text{nm}$. The slit separation is $0.450\,\text{mm}$. The distance from the slits to the screen is $1.50\,\text{m}$. A maximum is produced at $P_1$ and a minimum is produced at $P_2$. Interference fringes are seen only when the light from the slits is coherent.
(a(i))[2]
Explain the meaning of coherence.
(a(ii))[1]
Explain how an interference maximum is produced at $P_1$.
(a(iii))[1]
Explain how an interference minimum is produced at $P_2$.
(a(iv))[3]
Calculate the fringe spacing.
(b)[3]
State the effects, if any, on the fringes when the amplitude of the waves reaching the double slits is increased.
Worked solution & mark scheme
This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Coherence: a constant phase difference between two waves” …