# Interference pattern problem

1. Mar 4, 2006

### kidia

Anyone can help me on this one.

A plane wave of wavelength $$\lambda$$= 550 nm is incident normally on an opaque screen with three narrow parallel slits separated by distance a= 2.3 mm. An interference pattern is observed on the other side of the screen at a large distance from it.
(a)At what angles are the first principal maxima adjacent to the central maximum?
(b)How does intensity, Imax, at the principal maxima compare to that from a single slit, I1?

in (a) can I use asin$$\theta$$=m$$\lambda$$ to get the angle?

2. Mar 4, 2006

### BananaMan

from my notes (as im studying this aswell) i believe your answer from (b) should lie.... or could possibly be I= N^2 * Io

for a i would use asin$$\theta$$=m$$\lambda$$ aswell but im not so sure on this one, optics isn't exactly my best subject at the moment

3. Mar 5, 2006

### kmcf

For a maximum, the amplitudes will add in phase when a.sin(theta) = lambda, if a is the slit-to-slit spacing. For a minimum, you have to figure out when 3 waves will add to zero. The intensity is proportional to the square of the sum of the amplitudes.