The equation relating velocity and wavelength is written below:
v = λf
where λ is the wavelength in m while f is frequency in 1/s.
Let's determine first the frequency from the speed of light:
c = distance/time, where c is the speed of light equal to 3×10⁸ m/s
3×10⁸ m/s = (300 mm)(1 m/1000 mm)/ time
time = 1×10⁻⁹ seconds
Since f = 1/t,
f = 1/1×10⁻⁹ seconds = 10⁹ s⁻¹
Thus,
v = (795×10⁻⁹ m)(10⁹ s⁻¹)
v = 795 m/s
