At the start, the transmission axis of the filter is vertical. It is then turned through $360^\circ$ while the plane of the filter stays perpendicular to the beam. On Fig. 5.2, draw a graph to show how the intensity of the light in the transmitted beam changes with the angle through which the transmission axis is turned.
The incident beam has an intensity of $7.6\,\text{W m}^{-2}$. When the transmission axis of the filter is at an angle $\theta$ to the vertical, the intensity of the transmitted beam is $4.2\,\text{W m}^{-2}$. Calculate angle $\theta$.
State what is meant by the diffraction of a wave.
A beam of light with wavelength $4.3 \times 10^{-7}\,\text{m}$ is incident normally on a diffraction grating in air, as shown in Fig. 5.3. The third-order diffraction maximum for the light is at an angle of $68^\circ$ to the direction of the incident light beam. Calculate the line spacing $d$ of the diffraction grating.
Find another wavelength of visible light that would also give a diffraction maximum at an angle of $68^\circ$.