Question

Unpolarized light with intensity I₀ shines through a series of two polarizing filters. The first is oriented 30° counter-clockwise from vertical and the second is oriented 60° clockwise from vertical.

a.) Find the light intensity as it emerges from the first filter (in terms of I₀).

b.) Find the light intensity as it emerges from the second filter (in terms of I₀).

Now a new polarizing filter (oriented vertically) is placed between the original two filters.

c.) Will the light intensity emerging from the 3-filter combination be different than the 2- filter combination in (b)? If so, find the new intensity. If not, then explain why.

Answer 1

a.) Find the light intensity as it emerges from the first filter (in terms of I₀)

here, angle does not matter as light is unpolarized, intensity will always be reduced to half.

so,

I = I_o / 2 W/m²

_____________

b) Find the light intensity as it emerges from the second filter (in terms of I₀ )

I = I_o / 2 * cos² 90

I = 0 W/m²

_________________

c)

Yes, intensity will be different when we add third polarizer, as we saw intensity went to zero with two polarizers.

it will be around

I = (I_o / 2 ) cos ² 30 cos² 60

0I = 0.09375 I_o