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**1. Homework Statement**

Two slits separated by a distance of d = 0.12mm are located at a distance of D = 780mm from a screen. The screen is oriented parallel to the plane of the slits. The slits are illuminated by a coherent light source with a wavelength of lambda = 549E-6 mm. The interference pattern shows a peak at the center of the screen (m=0) and then alternating minima and maxima.

7. [1pt]

What is the pathlength difference between the two waves from the two slits at the first (m=1) maximum on the screen?

**2. Homework Equations**

d*sintheta = m*wavelength

sintheta = y(dist bt two maxima) / D(distance to screen)

**3. The Attempt at a Solution**

I'm really confused about what the "pathlength difference" refers to. It doesn't specify it in the book. I know the angles take different paths to get to the same point because of the distance inbetween them, but is it asking for an angle???

I solved the problem for y using the above equations, and at the first maxima (m=1), y(distance between the two maxima) is 0.0036m. But I don't know where to go from there?