# Find spacing between slits in a double slit experiement

1. Dec 4, 2016

### mkematt96

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

2. Relevant equations
I = Imax cos^2 ((2pi/lambda)dsin(theta))

.81Imax = Imax cos^2 ((2pi/lambda)dsin(theta))

To shorten up my work I divided out the Imax

3. The attempt at a solution

Not sure where I am going wrong. Is the 2.65 deg not the theta I am suppose to use? I divided out the I max, square rooted both sides, took the inverse cos of the left side to cancel out the cos on the right. Then proceeded to do the algebra.

2. Dec 4, 2016

### TSny

Check your notes or textbook to see if the factor of 2 (shown in red above) should be there.

Also, when doing the calculation think about whether or not the angle obtained from the cos-1 should be in radians or degrees.

3. Dec 5, 2016

### mkematt96

That 2 shouldn't have been in my equation. I found the calculation of inv cos (.9) in radians instead of degrees. That then gave me the correct answer. Thanks for the help!