# Interference in 2D (wavefronts)

1. Jul 10, 2009

### ~ak~

1. The problem statement, all variables and given/known data
The figure shows the circular wave fronts emitted by two wave sources.

Make a table with rows labeled P, Q, and R and columns labeled r1, r2, $$\Delta$$r, and C/D. Fill in the table for points P, Q, and R, giving the distances as multiples of $$\lambda$$ and indicating, with a C or a D, whether the interference at that point is constructive or destructive

2. Relevant equations
no real formula, given, just count the rings in the wave front pattern

3. The attempt at a solution
so i got mostly everything except r2 for P and R...im thinking it should be 7/2$$\lambda$$ for both, but apparently its not...what am i doing wrong?

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2. Jul 10, 2009

### Redbelly98

Staff Emeritus
Welcome to Physics forums.

Is the distance from "2" to the smallest ring equal to λ or λ/2?

What did you get for r2 and Q, that was verified as correct?

3. Jul 11, 2009

### ~ak~

thanks a lot redbelly...i cant believe i missed that, but i do have another question regarding this question. I can see that the 2 sources are out of phase but the only explanation that I can give is that 2 in-phase sources emit circular or spherical waves and these 2 dont. Is that correct?

4. Jul 11, 2009

### Redbelly98

Staff Emeritus
Not quite, out-of-phase point sources emit circular or spherical waves as well. It's just a matter of accounting for that phase difference when figuring out where there's constructive or destructive interference.