AP EAMCET Engineering 26 Apr 2017 Shift 1 Paper

The formula for the fringe width is,β=

λd

D

Substitute the given values in the above equation.
β=

(120×10−2)(0.5×10−9)

500×10−9

β=12×10−4m
The number of fringes in 3‌mm distance on screen is,
n=

3mm

12×10−4

n=

3×10−3

12×10−4

=25
That is third fringe.
The phase difference is,
ϕ=2π+2π+π
ϕ=5π