# Diffraction Grating Problem, brightness maximum involved

1. Mar 12, 2009

### NCyellow

1. The problem statement, all variables and given/known data
A bulb emits a continuous spectrum of ultraviolet, visible and infrared light in the wavelength range 360nm to 2000nm. Assume that the light from this bulb is incident on a diffraction grating with slit spacing d and that the first-order brightness maximum for the wavelength of 1200 nm occurs at angle (theta). What other wavelengths within the spectrum of incident light will produce a brightness maximum at this same angle (theta)?

2. Relevant equations
sin(theta) = m(lamda)/d
where m is an integer representing the order, and d is the distance between grating lines. Lamda represents the wavelengths of the light.

3. The attempt at a solution
Since I am given a lamda (wavelength) and an order, I set up my equation for theta as
(theta) = arcsin (1200nm/d)
I have no idea what the problem is asking for.
Thanks

2. Mar 12, 2009

### dslowik

Are you familiar with the geometry, what d , theta are? that really helps thinking these through.
otherwise, "first-order" refers to m=1 in that equation for the location(theta) of brightness maxima.
The question should make sense now.

3. Mar 12, 2009

### NCyellow

I went back to look in my textbook, but I am still confused by what you mean. I know that d is the separation between slits, D is the actual width of each slit, and theta is the angular spread. I am still confused however.

4. Mar 13, 2009

### dslowik

can u post the figure?
Otherwise, that m(lambda) is just the requirement to get constructive interference. m(lambda) can equal the same number for different combinations of m and lambda...