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Oijl

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## Homework Statement

Assume that the limits of the visible spectrum are arbitrarily chosen as 430 and 680 nm. Calculate the number of rulings per millimeter of a grating that will spread the first-order spectrum through an angle of 20.0 degrees.

## Homework Equations

(y is lambda)

dsinø = my (maxima)

## The Attempt at a Solution

So, the first-order spectrum of white light has a line (maxima) the lowest wavelength and another line at the highest wavelength - right?

And for the first-order spectrum would have a m of 1, right?

If this is true, then,

dsin(ø1) = 430

dsin(ø2) = 680

And, ø2 - ø1 = 20 degrees

And

ø1 = arcsin(430/d)

ø2 = arcsin(680/d)

But, I want to find out d. How can I extract d from these equations?

Or, alternatively, do I not understand what's going on?