Homework Help: Physics

Posted by EM on Sunday, March 7, 2010 at 6:14pm.

Light from a sodium lamp ( wavelength= 589 nm) illuminates a narrow slit and is observed on a screen 75 cm behind the slit. The dstance between the first and third dark fringes is 7.5 mm. What is the width (in mm) of the slit?

Cant seem to get the answer =/

Physics - drwls, Sunday, March 7, 2010 at 6:40pm
Read the "single slit diffraction" section of
http://en.wikipedia.org/wiki/Diffraction
The formula you need can be found there.

The angle theta at any distance x from the central maximum is
theta = tan^-1 (x/75)
where x is in cm
Physics - EM, Sunday, March 7, 2010 at 7:12pm
I've tried that and im still not getting the answer (which is 0.12 mm) =/ i used that formula to give me the theta and i substituted that into the d= lambda/ sin theta

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