# Homework Help: Light : colour and wavelength

1. Jun 9, 2012

### wow22

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

a certain young's apparatus has slits 0.12 mm apart. the screen is at a distance of 0.80 m. the third bright line to one side of the centre in the resulting interference pattern is displaced 9.0mm from the central line. calculate the wavelength of the light used. What colour is it?

2. Relevant equations

wavelength= xd/L
d= seperation=0.12mm = 1.2*10^(-4)m
x= distance from screen= 0.80m divided by 3 lines aka 2 wavelengths so 0.80m/2=0.40m?
L= pattern intereference distance= 9.0mm=0.009m=9.0*10^(-3)

3. The attempt at a solution
wavelength = xd/L
=(0.40m)(1.2*10^(-4)) DIVIDED BY 9.0*10^(-3)
=0.00533333
=5.3*10^(-3)m

Thanks in advance for any help!

2. Jun 9, 2012

### aznking1

Use the formula x= (wavelength x D)/a where x is the fringe separation, D is the distance from the double slits to the screen and a is the separation of the two slits

fringe separation = 9/3 = 3mm

D = 0.8m

A = 0.12mm

convert all units to M. and you can find wavelength

u will get 4.5*10^-7m. i have tried it.

3. Jun 10, 2012

### wow22

oh thankyouu!