   Chapter 27, Problem 32CQ

Chapter
Section
Textbook Problem

No light passes through two perfect polarizing filters with perpendicular axes. However, if a third polarizing filter is placed between the original two, some light can pass. Why is this? Under what circumstances does most of the light pass?

To determine

The reason for to pass some light through two perfect polarizing filter with perpendicular axes when a third polarizing filter is placed between them and the circumstances under which most of light pass.

Explanation

Introduction:

The polarization axis of a polarizing filter acts as a slit passing through electric fields parallel to its direction.

The intensity of light after passing through a polarizing filter is given by,

I=I0cos2θ   ....... (1)

Where, I0 is the intensity of original light and θ is the angle between the axis of polarizing filter and direction of polarization of light.

When light passes through first polarizing filter, it gets polarized in the direction of polarizing axis of first filter. The second filter is perpendicular to the first it means angle θ=90° . Thus, from equation (1), we get zero intensity of light after passing through second filter. Hence, we get no light.

Now, we place at third filter in between them making angle other than 90° with the other two

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