# Diffraction grating question

1. May 31, 2012

### dlucia

Question: Light from a slit passes through a transmission diffraction grating of 475 lines/mm, which is located 2.8m from a screen. What are the distances on the screen (from the unscattered slit image) of the three birghtest (first-order, n=1) hydrogen lines for red 657nm, blue-green 486nm, and violet 434nm.

I do not even know where to begin to solve this equation. The help is much appreciated.

2. Jun 1, 2012

### tiny-tim

(please use the homework template in future)

what equations do you know that might be relevant?

3. Jun 1, 2012

### dlucia

dsin(theta)=n(lambda)

4. Jun 1, 2012

### tiny-tim

ok, now apply that equation to the figures in the question …

what do you get?

5. Jun 1, 2012

### dlucia

I dont know what to do with the theta, since it is not given. and would i say that 1/d=the 475 mm/lines?

6. Jun 1, 2012

### dlucia

and the final units needs to be in cm

7. Jun 1, 2012

### sophiecentaur

Personally, I'd do all the calculations in m and then, if demanded, change the final answer to cm.

8. Jun 1, 2012

### dlucia

I have been trying everything under the sun and still can not get the answer right. i used the equation x=n(lambda)L/d
L=2.8m
Lambda= 657nm
d=(475 lines/mm)^-1

am I incorrect with that or no? Because the answer is still wrong for finding the distance between the slits.

9. Jun 2, 2012

### tiny-tim

show us your actual calculation and results