Hey how did you guys do the double slit question to find the frequency? (Can’t remember the question very well but I was a bit stumped and ended up doing something, don’t know if it was right)

I can't quite remember the question either but what the question was assessing was the knowledge that at local maximums (so the points labeled on the graph) the path difference is a multiple of the wavelength. At point p3 (I think that's what it asked) the path difference must be 3 times the wavelength in order for constructive interference to occur and since they give you the path difference you can solve for the wavelength and then obtain the frequency.

To clarify:

The path difference is the difference in distance light from each slit has to travel to one point. At each of the local maximums, the path difference needs to be a factor of the lights wavelength so that the waves constructively interfere (crests align with crests, troughs with troughs). At p0, the path difference is 0 (or 0*wavelength) and p1 the path difference is 1*wavelength and do on for all the values of p.

It then follows that local minima occur between these points and have path differences of multiples of half the wavelength so that troughs align with crests and crests align with troughs to result in destructive interference.

Hopefully with clears things up, but feel free point out anything I didn't explain very well.