What Is the Fringe Width in Young's Double Slit Experiment with Red Light?

[ibysaiyan]

Homework Statement

In a Youngs dbl. slit experiment using green light the fringe width was observed to be 0.20mm.if red light replaces green light,what will be the fringe width?

Homework Equations

hmm lambda=ay/d but (no info is given on rest)=/
wavelengths:green=5.2x10^-7m ,red=6.5x10^-7m

The Attempt at a Solution

well i don't know if its correct but i tried to solve it.by dividing the wavelength of of red over greens and i got 1.25m which i multiplied to (2x10^-4) <---- which is the fringe width of green .=/ i totally made it up .sos here =)

 

[The Bob]

Hey ibysaiyan,

Your method is right but now I want you to explain why it is. What do we know about d, n and L in the equation:

$$n \lambda \ = \ \frac{xd}{L}$$

in relation to this question?

The Bob

http://en.wikipedia.org/wiki/Double-slit_experiment