Answer:
6593.4
Explanation:
wavelength, λ = 910 nm = 910 x 10^-9 m
Speed of laser = 3 x 10^8 m/s
t = 20 pico seconds
Distance traveled by laser in this time, d = c x t
d = 3 x 10^8 x 20 x 10^-12 = 6 x 10^-3 m
number of wavelengths, n = d / λ
n = (6 x 10^-3) / (910 x 10^-9)
n = 6593.4
