# Homework Help: Diffraction Question: Calculating m

1. May 1, 2007

### cheechnchong

Diffraction Question: Calculating m....

1. The problem statement, all variables and given/known data

There are 5620 lines per centimeter in a grating that is used with light whose wavelength is 471 nm. A flat observation screen is located at a distance of 0.750 m from the grating. What is the minimum width that the screen must have so the centers of all the principal maxima formed on either side of the central maximum fall on the screen?

2. Relevant equations

sin(theta) = m*wavelength/width

3. The attempt at a solution

I realized that we were missing m from the problem...so I setup the equation sin (theta) = m*wavelength/w = m (471 x 10^-9 m/ .01/5620) = 0.265m

I can't proceed from there...It's quite confusing. can someone help me complete this problem??? Thanks!

By the way, the book answer is 1.95 m

2. May 1, 2007

### Mentz114

The principal maxima are given when m = +1 and m=-1. Calculate the angle between them, then use the distance between the screen and grating to get the spread. Draw a diagram.