Question

The frequency of a radiation having wavelength 900 nm is​

Answer 1

Use a photometer to measure the energy of a wave.

Convert the energy into joules (J).

Divide the energy by Planck's constant, 6.626 x 10-34, to get the frequency of the wave.

Divide the speed of light, ~300,000,000 m/s, by the frequency to get wavelength.