# Homework Help: Width of the slit

1. Sep 12, 2014

### somecelxis

1. The problem statement, all variables and given/known data
Monochromatic light of wavelength 550nm is used to illuminate normally a narrow slit. A converging lens of focal length 50cm is used to focus the diffraction pattern onto a screen. If the seperation between the first minima is 10.0mm What is the width of the slit. The ans is 0.055mm.

2. Relevant equations

3. The attempt at a solution
by using formula x= λD/ a ,
i have 10x10^-3 = (550x10^-9) x ( 50x10^-2) / (a) ,
i get my a = 0.0275mm ... What's wrong with my working?

2. Sep 12, 2014

### TSny

Is this formula meant to give the distance between the two first-order minima or is it meant to give the distance between the central maximum and one of the first-order minima?

3. Sep 13, 2014

### desmond iking

I guess the op means the distance between two first min is x ?

4. Sep 13, 2014

### somecelxis

In the working above I assume the x is distance between two first minimum... Anything wrong with it?

5. Sep 13, 2014

### ehild

x is the distance of any of the first minima from the central maximum.

ehild