# DIffraction vs. Inteference Help!

1. May 19, 2007

### IMGOOD

I know that in a double-slit experiment, the diffraction of the individual slits produces the envelope of the intensity pattern whereas the interference between the waves coming from the slits produces those little wiggles within that envelope.

But what exactly is the difference between diffraction and interference other than how they affect the intensity pattern? Interference make sense to me because, physically, it is just applying the principle of superposition and adding the waves up. But I can't imagine a similar physical picture for diffraction.

Also, how is it possible, in principle, to have interference without diffraction (in the context of slits)?

2. May 19, 2007

### mgb_phys

Interference is, as you say, adding together of two waves
Diffraction is just one way of creating two different waves.
In a double slit you split the wavefront into two and combine them again, in single slit it is easiest to think of the waves from the two edges of the slit.

3. May 20, 2007

### Staff: Mentor

Diffraction is just a more general application of the principle of interference.

Most textbooks present interference as the superposition (addition) of just two waves, or possibly a discrete number of waves (2, 3, 4, etc. slits)

In diffraction from a single slit, you have the superposition of an infinite number of waves, from each of the points across the width of the slit. Mathematically, you analyze this by integrating (rather than simply adding) the contributions from the various sections of the slit. In the full analysis of two-slit interference, you integrate over two regions (corresponding to two slits) and then add the two integrals.