Explain the role of diffraction in forming the fringes.
Explain why a double slit is used instead of two separate light sources.
An interference pattern is seen on the screen AB. The slit separation is $0.48\ \text{mm}$. The slits are $2.4\ \text{m}$ from AB. The distance across 16 fringes on the screen is $36\ \text{mm}$. Calculate the wavelength of the laser light.
Two dippers $D_1$ and $D_2$ produce identical waves on the water surface, as shown in Fig. 6.3. Point P is $7.2\,\text{cm}$ from $D_1$ and $11.2\,\text{cm}$ from $D_2$. The wavelength of the waves is $1.6\,\text{cm}$. The phase difference between the waves generated at $D_1$ and $D_2$ is zero.
State and explain the observation at P.
State and explain the effect on the answer to c(i) if the apparatus is changed so that, separately, the phase difference between the waves at $D_1$ and $D_2$ is $180^{\circ}$.
State and explain the effect on the answer to c(i) if the apparatus is changed so that, separately, the intensity of the wave from $D_1$ is less than the intensity of that from $D_2$.