Light Diffraction Grating!

1. Jun 8, 2014

Rookie

1. The problem statement, all variables and given/known data
A source of light shines through two apertures resulting in an intensity distribution pattern on a viewing screen.

The central bright fringe is called the m=0 or zeroth order maximum.

In the schematic diagram 1, the light source is to the left of the page and the point P represents the position of the second order intensity maximum on the screen. Two rays r1 and r2 are depicted incident at P.

Calculate the separation d of the two apertures, given the wavelength of the light is 600nm, L = 2m, Y = 5cm.
Remember that δ is the path difference between the rays (vectors) r1 and r2.

Hint: We need to be able to relate δ to the order number and the wavelength of the light.

2. Relevant equations

3. The attempt at a solution
From wikipedia it says that dsinθm = mλ
I assume I need mλ to find out separation d of the two apertures.
λ = 600nm, L = 2m, Y = 5cm
m = 0
I'm not sure how to comprehend the wavelength.
I really need someone to explain what I need to do here.
Any help would be grand!!

2. Jun 8, 2014

CWatters

Check you understand what "m" is in this equation..

Then check what value "m" is when...

3. Jun 8, 2014

Rookie

Ahh second order, I had m = 0 which is zeroth order.
So m should equal 2?