# Homework Help: Young's Double Slit vs. Diffraction grating

1. Aug 3, 2006

### User Name

I've been working on my Physics work when I scanned across a section and noticed something that bothered me.

The equation: d sin (thetha) = m (wavelength).

d is the separation and m is an interger.

However, it said to find the bright fringes of a double slit (Young's Double Slit Experiment), use this equation, and also to use this equation for the principal maxima of a diffraction grating.

Is there a difference? Are they just two different fancy names for finding the same thing?

Also, there's an equation I have to find: x ~ (wavelength)mL/d

x being position, m being an interger, L being distance and d being separation.

Is that related to the previous equation?

2. Aug 3, 2006

### HallsofIvy

No, they aren't the same thing although they are closely related. "Young's double slit" experiment, as the name implies, involves exactly two slits that are very close together. The diffraction pattern is a single central maximum with a number of smaller local maxima on either side (getting smaller as you move away from the central maximum). A diffraction grating involves a large number of slits (you take the number to be infinite) also very close together. It's diffraction pattern is periodic.