Question

You want to photograph a circular diffraction pattern whose central maximum has a diameter of 1.0 cm . You have a helium-neon laser (?=633nm) and a 0.12 mm -diameter pinhole.

Answer 1

Given :-

Diameter of the central maximum, D = 1 cm

r = D/2 = 0.5 cm = 5 x 10^-3 m

= 633 nm = 633 x 10^-9 m

d = 0.12 mm = 1.2 x 10^-4 m

Diffraction through circular aperture,

= 1.22 / d

is the angle of resolution,

= r / L

R/L =  1.22 / d

L = d*r / 1.22

L = (1.2 x 10^-4 x 5 x 10^-3) / (1.22 x 633 x 10^-9)

L = 0.777 m

Hence, distance the viewing screen is placed at 0.777 m behind the pinhole