A sheet of paper $0\mathrm{.}012cm$ thick separates two sheets of glass to form an air wedge $10\mathrm{.}8cm$ long.

When the air wedge is illuminated with monochromatic light, the distance between the centres of the

first and eighth dark bands is $2\mathrm{.}4mm.$ Determine the wavelength of the light. kru $[$ans: $7\mathrm{.}6{10}^{-7}m]$