Light of intensity I0 and polarized horizontally passes through three polarizes. The first and third polarizing axes are horizontal, but the second one is oriented 20.0� to the horizontal. In terms of I0, what is the intensity of the light that passes through the set of polarizers? A) 0.442 I0
B) 0.180 I0
C) 0.780 I0
D) 0.883 I0

Option C.

Explanation:

Suppose that we have light polarized in some given direction with an intensity I0, and it passes through a polarizer that has an angle θ with respect to the polarization of the light, the intensity that comes out of the polarizer will be:

I(θ) = I0*cos^2(θ)

Ok, we know that the light is polarized horizontally and comes with an intensity I0

The first polarizer axis is horizontal, then the intensity after this polarizer is:

then θ = 0°

I(0°) = I0*cos^2(0°) = I0

The intensity does not change. The axis of polarization does not change.

The second polarizer is oriented at 20° from the horizontal, then the intensity that comes out of this polarizer is:

I(20°) =  I0*cos^2(20°) = I0*0.88

And the axis of polarization of the light that comes out is now 20° from the horizontal

Now the light passes through the last polarizer, which has an axis oriented horizontally, so the final intensity of the light will be:

note that here the initial polarization is  I0*0.88

and the angle between the axis is 20° again.

Then the final intensity is:

I(20°) =  I0*0.88*cos^2(20°) = I0*0.78

Then the correct option is C.

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