# Singe Slit Diffraction

1. May 25, 2005

### drunkenfool

Hey, I have a problem here involving single slit diffraction, and it's stumped me.

A single slit is illuminated with a 660-nm light, and the resulting diffraction pattern is viewed on a screen 2.3 m away. If the linear distance between the first and second dark fringes is 12 cm, what is the width of the slit?

I want to use this formula to start me off:

y= L tan (theta)

But what value of y should I use? It can't be 12 cm, because that's defining the distance between those two dark fringes, not their distance to the central bright fringe.

Any ideas?

2. May 26, 2005

### OlderDan

The notation is a bit different, but take a look at the diagram and the equation here.

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/fraungeo.html#c2

You have two different y values corresponding to two different values of m, and all you know is the difference between the y values. You can use the equations to take the difference between the y values for the two m values and relate that difference to the distance to the screen and the slit width.