# Double slit experiment problem

## Homework Statement

monochromatic light of 625 nm of wavelength falls normal to the optical bar. Total number of light lines that appear behind the bar is 11. What is the constant of the difraction bar?

## Homework Equations

3. The Attempt at a Solution [/B]
I tried ##dsinx=ms## where ##s## is the wavelength and ##m## is number of lines. Since x is 90 i can calculate the ##d## to find the distance between the slits but what is diffraction constant?

TSny
Homework Helper
Gold Member
"Constant of the diffraction bar" might be referring to the "grating constant". The grating constant usually denotes the number of lines of the grating per unit length (often given as lines per millimeter). However, I've also seen people refer to the distance between two lines as the grating constant. So, you might need to consult your notes or textbook to see how it is used in your course.

I think it is lines per mm, is that 1/d?

TSny
Homework Helper
Gold Member
I think it is lines per mm, is that 1/d?
Yes. If you express d in mm, then you can think of d as the number of mm per line (mm/line). So, the units for 1/d would be .....?

TSny
Homework Helper
Gold Member
Your title for this thread refers to "double slit". But the question refers to a "diffraction bar", which I was thinking might be a diffraction grating. So, I'm not sure what you're actually dealing with here.