Double-slit interference: At most, how many bright fringes can be formed on each side of the central bright fringe (not counting the central bright fringe) when light of 625 nm falls on a double slit whose spacing is
A) 1
B) 2
C) 3
D) 4
E) 5

Question

Double-slit interference: At most, how many bright fringes can be formed on each side of the central bright fringe (not counting the central bright fringe) when light of 625 nm falls on a double slit whose spacing is 
A) 1 
B) 2 
C) 3 
D) 4 
E) 5

Quizplus · Accepted Answer

The number of bright fringes on each side of the central bright fringe is given by the formula mλd/D, where m is an integer, λ is the wavelength of the light, d is the slit spacing, and D is the distance from the slits to the screen. Plugging in the given values, we get 3 bright fringes on each side of the central bright fringe, for a total of 6 bright fringes. However, we are not counting the central bright fringe, so the answer is 3.

Double-Slit Interference: at Most, How Many Bright Fringes Can Be