Question

What does a do polaroid consist of? Show, using a simple polaroid, that light waves are transverse in nature. The intensity of light coming out of a Polaroid does not change irrespective of the orientation of the pass axis of the polaroid. Explain why.

Answer 1

A Polaroid consists of long-chain molecules aligned in a particular direction. To show light waves are transverse in nature: Take two polaroids T${}_1$ and T${}_2$ cut with their faces parallel to the axis of the crystal.

When Polaroid T${}_1$ is rotated about the direction of the propagation of light as an axis, the intensity of the transmitted light remains the same. When T${}_2$ is rotated gradually, the intensity goes on decreasing and the transmitted light disappears completely when T${}_2$ is perpendicular to T${}_1$. This happens because the polaroid allows only those vibrations of light which are parallel to its axis. This is true only if the light has vibrations in all possible directions and hence is a transverse wave.

Light waves are transverse waves. So, they have electric vectors in all possible directions. When a Polaroid is placed in between the path of the light, the electric vectors which are parallel to the pass-axis of the polaroid pass through it. Even if the polaroid is rotated, there would be other electric vectors which pass through it. So, the intensity of light does not change irrespective of the orientation of pass-axis of the polaroid.