# Help Required ly in this light problem

1. Mar 6, 2005

### shaiqbashir

Help Required urgently in this light problem

Hi !

can any body help me in solving this problem!

The electric field at Poin P due to N slits is,

A(r,$$\theta$$,t) =A(r) $$\frac{\sin\frac{1}{2}\N\Delta\phi\cos(kr-\omega\ t)}{\sin\frac{1}{2}\Delta\phi}$$

where $$\Delta\phi$$ =kd$$\sin\theta$$,

"d" being the spacing between adjacent slits.Let N=4.

a) Find two anglws on either side of $$\theta$$=0 at which there is an interference minima.
b)Find the spacing between the minima compare tp the case pf only two slits of separation "d".

I have solved its "a" part but i just couldnt solve its "b" part. Plz help mw in solving this:

Thanks a lot!