State, with reference to the direction in which energy is propagated, what a longitudinal wave means.
State what the principle of superposition is.
Calculate the wavelength, in $\text{nm}$, of the light.
The wavelength of light from a laser is found using the apparatus shown in Fig. 4.1. The laser light falls normally on the plane of the double slit. The slit separation is $3.7 \times 10^{-4}\,\text{m}$. The screen is parallel to the plane of the double slit. The screen is $2.3\,\text{m}$ from the double slit. Bright fringes and dark fringes are seen on the screen. The distance between adjacent bright fringes on the screen is $4.3 \times 10^{-3}\,\text{m}$.
Initially, the light passing through each slit had the same intensity. The intensity through one slit is now reduced. Compare the fringe pattern before and after the change in intensity.