Homework Help: Destructive interference and fringes

1. Nov 26, 2007

Joza

I am looking for the distance between the 2nd and 3rd DARK fringes on a screen.

Monochromatic, coherent light is shone through 2 slits a distance d apart.

Wavelength is L. Distance between grating and screen is R.

The formula I am using is: [(R(5/2)L)/d - (R(3/2)L)/d]

I am using 5/2 and 3/2 since these should be the number of wavelengths for destructive interference for the 3rd and 2nd fringes respectively.

The formula doesn't seem to be working though. Where have I gone wrong????

2. Nov 26, 2007

Joza

BUMP!

Come on guys. Any help? I really need to get this sorted today.

3. Nov 26, 2007

Staff: Mentor

Your formula looks OK to me. Why do you think its wrong?

4. Nov 26, 2007

Joza

I feel like an idiot.

Ah it was a classic unit conversion error!

Thanks tho!

5. Nov 26, 2007

Staff: Mentor

D'oh! (Been there, done that.)

6. Nov 26, 2007

Joza

Could you help me with my final part so?

7. Nov 26, 2007

Staff: Mentor

Final part of what?

8. Nov 26, 2007

Joza

I have 2 questions relating to light. This is one. I have posted the other. It is do with interference in a film.

Please excuse the posts in the thread. The first one relates to the question.