Question

Two identical rectangular slits 5 mm apart are illuminated with a monochromatic light of wavelength 600 nm. The screen is kept 1.2 m away from the slits.

1. Calculate the distance between the 5^th bright fringe (band) on one side and the 3^rd bright fringe on the other side of the central bright band.
2. What will be the change in the interference pattern if the given light is replaced with monochromatic light of wavelength 500 nm?

Answer 1

i. The distance between the 5^th bright fringe on one side and the 3^rd bright fringe on the other side of the control bright band:

= `5 (D lambda)/d + 3 (D lambda)/d`

= `8 (D lambda)/d`

= `(8 xx 1.2 xx 600 xx 10^-9)/(5 xx 10^-3)`

= 115.2 × 10⁻⁵ m

ii. The fringe width of the interference will decrease.