- #1

JJBladester

Gold Member

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## Homework Statement

This is the interference pattern on a viewing screen behind two slits.

(image of 7 bright fringes with black fringes between every pair of bright fringes)

How would the pattern change if the two slits were replaced by 20 slits having the

*same spacing d*between adjacent slits? Would the number of fringes on the screen increase, decrease, or stay the same?

## Homework Equations

dsin(theta)=m(lambda)

## The Attempt at a Solution

The formula above says that for constructive interference, the path-length difference between successive slits needs to be an integer multiple of wavelength (lambda). However, I don't see anything in my book about the number of fringes going up or down with N (the number of slits) on the grating. Any advice?

I know that the fringe spacing increases, the width of each fringe decreases, and the brigntness of each fringe increases, but I don't know about the *number* of fringes and whether it goes up or down.