Unpolarised light travels through two polarising filters X and Y and is then incident on a screen - AQA - A-Level Physics - Question 17 - 2020 - Paper 1

To solve this problem, we need to apply Malus's Law, which states that the intensity of light passing through a polariser is given by:

$I = I_0 \cos^2(\theta)$

where:

• $I_0$ is the initial intensity of light that is unpolarised.
• $\theta$ is the angle between the light's polarisation direction and the axis of the polariser.

Maximum intensity will occur when $\theta$ is an integral multiple of $\pi$, because at these angles, the light is fully transmitted.

Since the problem states that we start with $\theta = 0$ (for max intensity), the angles where the intensity is maximised as $\theta$ increases would follow the pattern of:

• $\theta = n\pi$ for integer values of n.

The next three values where this occurs after $0$ are:

1. $\theta = \pi$ (1 complete rotation)
2. $\theta = 2\pi$ (2 complete rotations)
3. $\theta = 3\pi$ (3 complete rotations)

Thus the next three values for $\theta$ in radians where the maximum intensity occurs are:

• $\pi, 2\pi, 3\pi$.