An EM wave has a wavelength of 620 nm.

Question

What is its frequency?
How would we classify it?

Answer 1

620 nm = 620*10^-9 m. = 6.2*10^-7 m.

L = V/F.
F = V/L = 3*10^8m/s / 6.2*10^-7m = 4.839*10^14 cycles/s = 4.839*10^14 Hz.