Destructive Interference and path difference

[wendo]

Hi!

I hope I'm posting in the right place!

In the destructive interference of waves and solving for the path difference, I"m confused at when we should use m+1/2 vs. m-1/2 ( so the eq'n is PD=(m+1/2)lambda or PD=(m-1/2) lambda

Any insight would be greatly appreciated! :)

thanks!

 

[waht]

m is a number of how many dark spots away you are from the center. The sign determines which direction on the interference pattern from the center is your dark spot.

 

[Doc Al]

In the destructive interference of waves and solving for the path difference, I"m confused at when we should use m+1/2 vs. m-1/2 ( so the eq'n is PD=(m+1/2)lambda or PD=(m-1/2) lambda

If you're talking about double slit interference, then destructive interference (dark fringes) happen when the path difference is a 1/2, 3/2, 5/2, etc., multiple of the wavelength. So you can use PD=(m-1/2)lambda, where m stands for the number of the dark fringe (m = 1, 2, 3, etc.; first, second, third, etc., dark fringe) counting from the central maximum.