# Distance between two second order maxima

1. Sep 29, 2009

### kuzco890

1. The problem statement, all variables and given/known data
Monochromatic light strikes a diffraction grating at normal incidence before illuminating a screen 1.99 m away. If the first-order maxima are separated by 1.36 m on the screen, what is the distance between the two second-order maxima?

2. Relevant equations
I think these are the relevant equations:
deltaL = dsinθ
y = Ltanθ

3. The attempt at a solution
L = 1.99 m
I'm not sure where the 1.36 and 1.99 come in.

2. Sep 29, 2009

### Delphi51

3. Sep 29, 2009

### kuzco890

So I only need the d sinθ = mλ equation?
Would you be able to help walk me through it?
I feel like I need the y = Ltanθ or deltaL = dsinθ equation.
Doesn't L = 1.36 for the first order maxima?
d = 1.99 m
m = 2?

4. Sep 29, 2009

### Delphi51

Draw the triangle with theta, x (distance from center to maximum - half the 1.36), L (L is the hypotenuse), and the 1.99 m distance to the screen. Use the triangle and some trig to find theta.

Use the formula to find lambda/d. This value doesn't change as you move to 2nd order, so you can use the formula again with this value to find theta when m = 2.

5. Sep 30, 2009

Thanks!