Question

A polariod (I) is placed in front of a monochromatic source. Another polatiod (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, will light emerge from (II). Explain.

Answer 1

A polaroid (I) is placed in front of a monochromatic source. Another polaroid (II) is placed in front of this polaroid (I) when the pass axis of (II) is parallel to (I), light passes through polaroid-II unaffected.

Now polaroid (II) is rotated till no light passes. In this situation, the pass of polaroid (II) is perpendicular to polaroid (I) and then (I) and (II) are set in crossed positions. No light passes through polaroid-II.

Now third polaroid (III) is now placed in between (I) and (II). Only in the special cases when the pass axis of (III) is parallel to (I) or (II), there shall be no light emerging. In all other cases, there shall be light emerging because the pass axis of (II) is no longer perpendicular to the pass axis of (III).

Now polaroid (II) is rotated till no light passes. In this situation, the pass axis of polaroid (II) is perpendicular to polaroid (I) and then (I) and (II) are set in crossed positions. No light passes through polaroid-II.

Now third polaroid (III) is now placed in between (I) and (II). Only in the special cases when the pass axis of (III) is parallel to (I) or (II), there shall be no light emerging. In all other cases, there shall be light emerging because the pass axis of (II) is no longer perpendicular to the pass axis of (III).