Finding Incident Intensity for Unpolarized Light

[wiped_out]

Homework Statement

Two sheets of Polaroid are placed on top of each other with an angle φ between their pass
directions. Calculate be the ratio of transmitted to incident intensity for initially unpolarised
light if φ = 30°.I copied the question exactly, I'm pretty sure that typo wasn't on purpose but I left it there anyway.

Homework Equations

I0 = I'/2

Malus's Law
I = I0 cos^2 θ

The Attempt at a Solution

I used the equation above to do:

= I0 cos^2(30)
cos^2(30)=.75
.75 x .75 = .5625 = 9/16
= I0(9/16)

not sure if that is right

 

[rl.bhat]

When the unpolarised light is transmitted through a Polaroid, 50% of light is transmitted. So I' = Io/2
When it passes through second Polaroid, the intensity of transmitted light is
I" = Io/2*cos^2(θ)