What is the Separation of Two Apertures in a Light Diffraction Grating?

[Rookie]

Homework Statement

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.

Homework Equations

The Attempt at a Solution

From wikipedia it says that dsinθ_m = 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!

 

[CWatters]

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

dsinθm = mλ

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

point P represents the position of the second order intensity maximum

 

[Rookie]

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