In the two-slit experiment, the distance between the slits and the screen is 1.15 m and the distance between the slits is 0.100 mm. If the first-order bright fringe is measured to be 4.2 cm from the centerline, what is the wavelength of light?

Given,
D = 1.15 m (distance of slots from
screen)
d = 0.100 mm
10^-4 m (distance between the two slits)
m = 1 (first order bright fringe)
xm = 4.2 cm
0.042 m (distance of first order bright fringe from centreline)

We know that,
xm = m* D λ/d (λ= wavelength)
0.042 = 1* 1.15 λ/10^-4
λ = (0.042 * 10^-4)/1.15

Therefore,
λ = 0.0365 * 10^-4
3.65 * 10^-6 m (approx)