# Homework Help: Unpolarized Light Intensity

1. Sep 17, 2009

Unpolarized light from an incandescent lamp has an intensity 176 Cd as measured by a light meter. What is the intensity reading on the meter when two ideal are inserted between the bulb and the meter with their axis of polarization making an angle of θ = 40.0° relative to each other? Express your answer in Cd.

am having some trouble with this problem. Here's what I have so far:

Known info:

Io=28 Cd

Theta= 6o

There are two polarizers, so theta1=6 and theta2=6

Equations:

I= Io/2

Malus' Law: I= Iocos^2theta

Work:

I used this to try and solve and it is wrong...

I = 28/2

I=14

Then

I = 28(cos6)^2 which = 27.7 (at theta1)

but there are two polarizers so 27.7 becomes the new Io for theta2

I=27.7(cos6)^2 which =27.4

So you add them right? 27.7+27.4 which = 55.1?

Where am I getting confused?

2. Sep 17, 2009

### Redbelly98

Staff Emeritus
Welcome to PF.

For starters, the problem statement says 176 Cd and 40.0 degrees. Why are you using 28 Cd and 6 degrees when you work out the problem?