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## Homework Statement

You need to design a diffraction grating that will disperse the visible spectrum (400-700nm) over 30.0 degree in first order.

a) How many lines per millimeter does your grating need?

b) What is the first-order diffraction angle of light from a sodium lamp (wavelength = 589nm)?

## Homework Equations

dsin(theta) = m(wavelength)

## The Attempt at a Solution

m= 1 (as it is first order) wavelength = (400*10^-9)m

angle = 30 degree wavelength = (700*10^-9) m

I'm confused because there are two wavelengths given. Do I find the d value for both wavelength and then find difference between them ... d= 0.0000014-0.0000008 = 0.0000006 = 6*10^-7

then 1667lines/mmm

for part 2) do i use the d value as 6*10^-7

because other values are given ... wavelength = 589 *10^-9 and m=1

If I take the same d value I'm getting as 79 degree ... is it right ?

Please somebody check the calculation and tell if its right ... I've only one attempt left.

Can someone also tell me how to put equation on these kind of questions. I'll be very grateful.