# Homework Help: Lab Prep Help (diffraction and interference)

1. Nov 22, 2009

### KBriggs

1. The problem statement, all variables and given/known data
This is a second year physics lab on diffraction and interfererence. The theory is not given in the lab manual, and unfortuneately, all of the references they list are unavailable at the library.

So, I need some hep recalling a few equation that I am going to need. I am googling around for them now, but if anyone knows them and posts them here it might greatly speed up my search.

The apparatus is a single wavelength laser source passed through a lense to make the beam parallel and them the diffraction device to a wall. Angles are measured as the distance along the wall, divided by the distance to the wall.

Here are the instructions:

2.3 Measurements
Single Slit Draw:
a rough diagram of the diffraction pattern and take enough
measurements to determine the slit width accurately.

Double Slit Draw:
a rough diagram of the diffraction-interference pattern,
and take enough measurements to calculate the slit width and the slit
separation accurately

The Diffraction Grating:
Take enough measurements to determine the
grating constant accurately.

2. Relevant equations
I reccall that the double slit separation equation is:

$$a sin\theta = m\lambda$$
for a the slit separation
This formula also gives the locations of the minima for single slit interference, with a the slit width

and the diffraction grating constant equation is
$$d sin\theta = m\lambda$$
for d the diffraction grating slit width

But I forget the formulas for the slit width in the double slit case

3. The attempt at a solution
See above

Thanks!

Last edited: Nov 22, 2009