# Calculating the Fringe Width without the value of its Wavelength

1. Apr 14, 2010

### AJ786

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

Young's fringes, produced by monochromatic laser light passing through slits 0.60mm apart, are viewed on a screen. The distance accrose 20 fringe spacings on the screen is 58mm. When the screen is moved 0.80m away from the slits, the distance across 20 fringe spacings becomes 74mm.

2. Relevant equations

Y = D(lamda) / d

Y = Fringe Width
D = Distance from slits to screen
d = spacing between slits
(lamda) = Wavelength

3. The attempt at a solution

Last edited: Apr 14, 2010
2. Apr 14, 2010

### rl.bhat

In the experiment wavelength and slit width is constant. There fore
Y1/Y2 = D1/D2.
Y1 and Y2 is given. D1 is not given. But D2 = D1 + 0.80 m.
Substitute these values in the above relation and find D1.
Then using the relevant equation, you can find the wavelength.

3. Apr 14, 2010

### AJ786

Are Y1 and Y2 0.60mm and 74mm as Y is what I need to calculate so surely this would not be given to me within the question ?

Last edited: Apr 14, 2010