A Level Physics Practice Exam

What is the result when two polarizing filters are placed one in front of the other and the front filter is rotated in daylight?

1. Light remains constant

2. Complete darkness occurs

3. Variation in intensity between maximum and minimum occurs

4. No observable changes in light intensity

The correct answer is: Variation in intensity between maximum and minimum occurs

When two polarizing filters are aligned with respect to each other, the behavior of light passing through them is influenced by the orientation of the filters. When the front filter is rotated while the back filter remains fixed, the intensity of the transmitted light varies between maximum and minimum levels. When both filters are initially aligned (with their polarizing directions parallel), light passes through with maximum intensity. As you begin to rotate the front filter, the angle between the polarization axes of the two filters changes, affecting the amount of light that can pass through. This is described by Malus's Law, which states that the intensity of light transmitted through two polarizers is proportional to the square of the cosine of the angle between their axes. As the front filter is rotated from 0 to 90 degrees, the light intensity gradually decreases from its maximum value to zero, creating a variation in intensity. This means that there will be points of maximum (when aligned) and minimum (when perpendicular to each other) intensity, leading to the conclusion that there will be a variation in light intensity between these extremes. Therefore, the correct response about the outcome of the situation described is that there will indeed be a variation in intensity between maximum and minimum as the front filter is rotated.