Question

What will you observe if

1. you look at an unpolarized source of light through a polarizer,
2. you look at the source through two polarizers and rotate one of them around the path of light for one full rotation, and
3. instead of rotating only one polaroid, you rotate both polaroids simultaneously in the same direction?

Answer 1

1. The transmitted light becomes plane-polarized, and its intensity is reduced to half of the original intensity. \[I=\frac{I_{0}}{2}\]
2. The intensity of light varies continuously as the polarizer is rotated. It is maximum when the axes are parallel and zero when they are perpendicular, according to Malus’ law: \[I=I_{1}\cos^{2}\theta\] During one complete rotation, the intensity becomes maximum twice and zero twice.
3. If both polaroids are rotated together through the same angle, the angle between their axes remains unchanged. Therefore, the transmitted intensity remains constant, although the direction of polarization of the emerging light rotates.