Finding slit seperation in two-slit experiment

1. Nov 4, 2012

clearsky

1. The problem statement, all variables and given/known data

Light from a He-Ne laser ($\lambda$ = 632.8nm) strikes a pair of slits at normal incidence, forming a double-slit interference pattern on a screen located 1.50 from the slits. The figure shows the interference pattern observed on the screen

What is the slit separation?

2. Relevant equations

d*sin($\theta$) = m*sin($\lambda$)
y = L*sin($\theta$)

3. The attempt at a solution

I know i can solve this problem if i just find sin($\theta$) but this is where i'm getting stuck.

Also, does the diagram tell me anything important? i thought maybe by dividing the 23mm by 4, i could get y (the distance between each bright fringe) but that proved to be fruitless when i tried solving for sinθ using 0.023/4 = 1.5sinθ but that didn't give me the correct answer for d.

nevermind. i figured this out.

Last edited: Nov 4, 2012
2. Nov 5, 2012

Delphi51

The formula should be d*sin(θ) = m*λ.
Draw your diagram with one line horizontal from the slits to a bright central maximum and another line at angle θ to the next bright spot, separated from the first by x. You can figure out x from the given diagram and then you can get the hypotenuse in the new diagram using the Pythagorean theorem. Use the formula to solve for the slit separation distance d.