Check the accuracy of d sin(θ) = mλ and document how to easily check it in the future

[samreid]

For the ideal case double slit interference, maxima occur at d sin(θ) = mλ, where:

d is the distance between the centers of the slits
theta is the angle from the line between the slits
m=0,1,2,3,...
lambda is the wavelength

[samreid]

I pushed a version of the simulation that shows d sin(θ) = mλ and d sin(θ) = (m+1/2)λ. Here are some results:

I've noted this in the documentation. @arouinfar can you take a look on phettest with ?dev or maybe it is &dev and let me know your thoughts?

[arouinfar]

The ?dev overlay for 2-slit interference is really handy! I wonder if it should be its own query parameter that we could share with teachers in the production version.

The double-slit interference is behaving nicely and the physics looks correct to me.

For the single slit, I have not been able to produce an interference pattern. Have you had any luck with that @samreid?

[samreid]

@arouinfar is this single slit diffraction?

[arouinfar]

Yes, that's what I was looking for @samreid! Reducing the wavelength definitely does the trick. I was originally testing with red light.

One thing I'm noticing is that there doesn't appear to be a true minimum between the primary and secondary maxima. It's more apparent when the wavelength is a bit larger.

Do you have any thoughts about this @samreid?

[samreid]

I searched a bit more and found a better node here:

Perhaps noise and near-field effects are obscuring this physics. I don't know if single slit diffraction is a primary learning goal for this simulation, or if we should add a "dev" style overlay for single sit angles. What do you recommend?

[samreid]

Labeled for design meeting to see what else remains for this issue.

[arouinfar]

@samreid given that there's a single-slit scene and now a diffraction screen, I think we can say that single-slit diffraction is certainly an important phenomena to observe. Let's discuss more in design meeting.

An overlay for single-slit angles would certainly be handy, but let's pause until we discuss the fate of its double-slit analog.

[samreid]

The 2nd order maxima for single slit diffraction has a magnitude much smaller than the central (1st order) maximum:

https://en.wikipedia.org/wiki/Diffraction#Single-slit_diffraction

[arouinfar]

@samreid correct, but there should be regions of zero intensity between the maxima. The screenshots in #74 (comment) and #74 (comment) don't have very clear minima.

[samreid]

Perhaps noise and near-field effects are obscuring this physics.

Another possibility is interference from reflections at the boundaries of the lattice (which we haven't been able to eliminate completely).

[samreid]

We'll take the time to quantitatively check the single slit equation with an overlay.

[samreid]

@kathy-phet recommends ?theory for showing the rays. We won't show it for "Interference" screen. Just show it for the slits screen. Promote this code from "hack for testing" to production ready.

[samreid]

Outstanding work tracked in aforementioned issues, closing.