Two thin parallel slits that are 0.012 mm apart are illuminated by a laser beam of wavelength 650 nm. On a very large distant screen, the total number of bright fringes including the central fringe and those on both sides of it is

Options

A. 38
B. 37
C. 40
D. 39

Answer

b

Explanation

For constructive interference,
`d sin theta = n lambda`
`(sin theta)_(max) = 1`
`n_(max) = (d)/(lambda) = (0.012 xx 10^(-3))/(650 xx 10^(-9)) = 18.46`
Therefore, total number of bright fringes including the central fringe is `18 + 18 + 1 = 37`.