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## Homework Statement

White light containing wavelengths from 396 nm to 756 nm falls on a grating with 7300 lines/cm. How wide is the first-order spectrum on a screen 2.15 m away?

## Homework Equations

y=m*L*wavelenth/(d)

## The Attempt at a Solution

using the equation I have found y1 to be 62.149 and y2 118.635. I took the difference of the two which gave me 56.486 cm, but that is wrong for some reason. Please help.