Find spacing between slits in a double slit experiement

[mkematt96]

Homework Statement

2. Homework Equations
I = Imax cos^2 ((2pi/lambda)dsin(theta))

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

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.

 

[TSny]

Homework Equations

I = Imax cos^2 ((2pi/lambda)dsin(theta))[/B]

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.

 

[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!