What is the wavelength of light produced by the pointer?

A red laser from the physics lab is marked as producing 632.8 nm light. When light from this laser falls on two closely spaced slits, an interference pattern formed on a wall several meters away has bright fringes spaced 6.00 mm apart near the center of the pattern. When the laser is replaced by a small laser pointer, the fringes are 6.20 mm apart.What is the wavelength of light produced by the pointer?

The fringe width in the double slit interference pattern is given by

fringe width = D? / d

Where D = distance of the screen from the slits
d = separation between the slits

The wave length ? is directly proportional to the fringe width.

?1 / ?2 = 6 / 6.2
?2 = ?1 x 6.2 / 6 = 632.8 x 6.2 / 6 = 653.9 nm is the wave length of light produced by the pointer.