# Need help with capa questions

1. Apr 1, 2004

### Evergreen

need help with capa questions....

Two polarizers are oriented at 35.7o to each other and plane-polarized light is incident on them. If only 11.9 percent of the light gets through both of them, what was the initial polarization direction of the incident light?

White light containing wavelengths from 391 nm to 758 nm falls on a grating with 7770 lines/ cm. How wide is the first-order spectrum on a screen 2.40 m away?

just two questions, i have no clue....

2. Apr 2, 2004

### Staff: Mentor

Are you familiar with Malus' Law? It says that if linearly polarized light passes through a polarizer, the intensity of the light transmitted is I = Iincidentcos2(θ), where θ is the angle between the polarization direction of the incident light and the polarization axis (transmission axis) of the polarizer.
Take a peek at these threads:

3. Apr 2, 2004

### Evergreen

i need a numeric answer, for the second quesiton that I am posting, i did use a similar method, but my answer is still wrong

4. Apr 2, 2004

### Staff: Mentor

Show your work and I'll take a look.

Last edited: Apr 2, 2004
5. Jul 28, 2004

### PrettyMz4Christ

6. Jul 28, 2004

### Staff: Mentor

Law of Malus

That depends on what you are given in the problem. If you have a specific problem, post it and your work and I'll take a look. (You might want to start a new thread.)

I give a brief description of Malus' law in my earlier post.
Do a search on Malus' Law and you'll find plenty. Here's one place to start: http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/polcross.html#c3

Welcome to PF!