State the reason why sound waves cannot be polarised.
A plane-polarised light wave falls on a polarising filter, as shown in Fig. 5.1. The intensity of the light striking the filter is $I_0$. The light arrives normally at the filter, and at first the transmission axis of the filter is perpendicular to the plane of polarisation of the light. The filter is then turned through $360^{\circ}$ about the direction of travel of the light wave.
On Fig. 5.2, sketch how the transmitted-light intensity $I$ varies with rotation angle $\alpha$ as the filter is turned through $360^{\circ}$ from its starting position.
The amplitude of the incident light wave is $A_0$ when the wave intensity is $I_0$. Use Malus’s law to determine, in terms of $A_0$, the amplitude of the transmitted wave when $\alpha = 20^{\circ}$.
Apply Malus’s law to determine, in terms of $A_0$, the amplitude of the transmitted wave when $\alpha = 20^{\circ}$.