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**1. Homework Statement**

Coherent light with wavelength 585 nm passes through two very narrow slits that are

0.320 mm apart. The screen is 0.700 m away from the slits. The intensity is I0 at the

centre of the central maximum (theta=0)

(a) What is the phase difference (in radians) in the light from the two slits at an angle

of 23degrees from the centre line?

(b) What is the distance on the screen from the centre of the central maximum to the

point where the intensity has dropped to I0/2?

**2. Homework Equations**

Φ=2π/λ*dθ

I=I_0*cos

^{2}Φ/2

**3. The Attempt at a Solution**

a)

(2pi*3.2x10^-4)/(5.85x10^-7)*23pi/180=439pi radians

b) I=I_0cos^2(Φ/2)

cos^2((pi/2)/2)=1/2

So i figured Φ=2pi but the equation i wanted to use to solve is

Φ=(2*pi*d)/(λ)*θ

but i don't have a theta. For part a it was 23 but i figured there will be a completely new angle for this part of the question.

Thanks