# How to find theta in a mutiple slit question

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1. Oct 7, 2016

### MartinFreeman

1. The problem statement, all variables and given/known data

A diffraction grating with 14100 lines per 2.54 cm (i.e., per in.) is used to view the visible spectrum from a Hydrogen gas excited by an electrical discharge. At what angle from the beam axis will the first order peak for the red photons with wavelength of 0.656 μm occur?
2. Relevant equations

d sinΘ= m λ

3. The attempt at a solution

I think i've got the right awnser, but apparent not.

so here is what i've done , to get d : 0.0254m/14100 = 1.801E-6

Θ = sin^-1 ( 656E-9 / 1.801E-6 ) = 21.36ο .

However, this is not the correct answer. I was wondering how I might have made a mistake?

2. Oct 7, 2016

### MartinFreeman

I have a feeling that maybe this question is much more complicated than my 3 step calculation...

3. Oct 8, 2016

### lychette

What you have done is correct. What are you told is the correct answer?

4. Oct 10, 2016

### MartinFreeman

Unfortunately the system only accepts correct answers, but does not accept wrong awnsers, So... i don't know. But it's good to know i did the right work. Il mark it solved , thanks for your help.