Find angular seperation of spectral lines with a grating spectrometer

[sailfast775]

Homework Statement

find the angular separation between the red hydrogen-alpha spectral line at 656nm and the yellow sodium line at 589nm if the two are observed in third order with a 3500-line/cm grating spectrometer.

Homework Equations

maximum equation for multi-slit interference
d sin(theta)=m*lamda

d=distance between two slits
m=the interger called the order (bright spots)
theta=angular separation
lamda=wavelength

The Attempt at a Solution

I tried plugging all of my data into the equation above with d as 1/grading but I'm not sure if this is the right way to go about the problem. I'm not even sure if this is the best formula to use but I can't find any other relevant equations

 

[djeitnstine]

Welcome to Pf sailfast

you are correct, your d is 1/3500 to get centimeters per grating. This equation is correct and applies to this problem. Just be careful with your units and 'm'

 

[sailfast775]

yay! i rock at PHYS

 

[WenyiJones]

I have the same question here. But when I get sin(theta), I get something over 1. That is not possible. Is my equation wrong? Because I am very sure the units I've been using here are correct. I converted everything into meters.