# What is the minimum number of Polarizers needed

1. Mar 9, 2016

### ah011

1. The problem statement, all variables and given/known data
A polarized light is incident on several polarizing disks whose planes are parallel and centred on common axis. Suppose that the transmission axis of the first polarizer is rotated 25° relative to the axis of polarization of the incident light, and that the transmission axis of each additional analyzer is rotated 25° relative to the transmission axis of the previous one. What is the minimum number of polarizer needed (whole number), so the transmitted light through all polarizing sheets has an intensity that is less than 9% that striking the first polarizer?

2. Relevant equations

3. The attempt at a solution

Since the question is asking for the number of polarizers needed, you start by looking at 25 degrees take the cos^2(25). Then, since they are parallel and centered on a common axis it must be added to cos^2(25-9). Im not sure what to do after this.

2. Mar 9, 2016

### ah011

Can anyone reply this question is making me tear my hair out

3. Mar 9, 2016

### Qwertywerty

Hint : Intensity after passing through one polarizer is I0cos2250, after the second, I0cos4250, ...Do you see a general formula for the intensity after passing through x polarizers?

Also, you typically don't want to be the first one to reply to your own thread. It is no longer visible in the 'Unanswered Threads' column, and people are less likely to visit this thread.

4. Mar 9, 2016

### haruspex

That's a very strange conclusion. Where did you get the 9 degrees from? It makes me think you misunderstand the arrangement.