The Difference Between Diffraction And Interference Patterns

[PhysicsGuy12341]

I've recently come across this problem:

• Answer true or false. If light shines through 2 slits, will the diffraction pattern always be within the interference pattern.

I don't understand this question, however. How can the interference and diffraction pattern be separated in this situation? What's the difference? I don't understand what a diffraction pattern or and interference pattern is.

Can you please try to answer this question at the level of a high school student? I've tried looking at other sources, such as https://physics.stackexchange.com/q...between-diffraction-and-interference-of-light, but none of them give me a satisfactory and understandable explanation. They contain terms like "spatial frequency domain" that are just too complex for me to understand.

 

[haruspex]

This link http://electron6.phys.utk.edu/phys250/modules/module 1/diffraction_and_interference.htm gives a very clear explanation of the two phenomena, but I don't yet see how to use it to answer your question.

 

[PhysicsGuy12341]

Do you have a source that explains what diffraction and interference patterns are though? Because that source explains what diffraction and interference is, but I already know that. But what I need to know is what diffraction and interference patterns are, not what diffraction and interference is.

 

[haruspex]

what I need to know is what diffraction and interference patterns are

The answer seems so obvious that I feel I must be misunderstanding your difficulty. They're the patterns of dark and light bands produced by the two phenomena, as illustrated at that link.
You can figure out the details by applying the two sin(θ)= equations.

Normally, if discussing two-slit interference, the individual slits are too narrow (<λ) to be producing diffraction patterns. But suppose we make each slit the same width as the gap between them. There will be two diffraction patterns, one centred opposite each slit. In principle, these will have dark bands where sin(θ) is an even multiple of λ/2. There will also be an interference pattern centred opposite the mid point between the slits, with, in principle, dark bands where sin(θ) is an odd multiple of λ/2. I say "in principle" because the two effects will be overlaid and may to some extent cancel out.
To get a full understanding of what will be seen we would need to have a formula for the intensity at each point. I'll see if i can come up with one.

But I still don't really understand the question you are being asked. The dark bands extend as far as the last integer solution of the equation, in each case. E.g. for diffraction, sin(θ)=nλ/w, it would be the largest n for which nλ/w<1, i.e. w/λ rounded down.