Question

A polariod (I) is placed infront of a monochromatic source. Another polariod (II) is placed in front of this polaroid (I) and rotated till no light passes. A third polaroid (III) is now placed in between (I) and (II). In this case, wil light emerge from (II) . Explain.

Answer 1

In the diagram shown, a monochromatic light is placed infront of polaroid (I) as shown below.

As per given question, monochromatic light emerging from polaroid (I) is plane polarised. When polaroid (II) is placed in front of this polaroid (I), and rotated till no light passes through polaroid (II), then (I) and (II) are set in crossed positions, i.e., pass axes of I and II are at `90^(@)`.

Consider the above diagram where a third polaroid (III) is placed between polaroid (I) and polaroid (II).
When a third polaroid (III) is placed in between (I) and (II), no light will emerge from (II), if pass axis of (III) is prallel to pass axis of (I) of (II). In all other cases, light will emerge from (II), as pass axis of (II) will no longer be at `90^(@)` to the pass axis of (III).