Light of wavelength 565 nm is used to illuminate normally tw

Light of wavelength 565 nm is used to illuminate normally two glass plates 23.8 cm in length that touch at one end and are separated at the other by a wire of radius 0.022 mm. How many bright fringes appear along the total length of the plates.

Solution

slit width, a = 0.022mm = 0.022 x 10^-3 m

wavelength, lambda = 565 nm = 565 x 10^-9 m

for bright fringe,

sin@ = m * lambda / a

sin90 = m * (565 x 10^-9) / (0.022 x 10^-3)

m = 38.94

hence 38 fringes will appear.