First convert the wavelength to meters:
λ = 3.835 × 10^−7 cm is 0.003835 in meters
The speed of light is:
C = 3.0 × 10^8 m/s
Frequency is the speed the wavelength:
f = C/λ where c is speed of light and λ is the length of the wave
f = 3 × 10^8 m/s/ 0.003835 m
f = 7.8227 × 10^10 Hz
