I have the energy and frequency of a light source and I need the wavelength and colour. What do I do?
speed = c = 3*10^8 m/s close enough
p = period = 1/frequency
the light goes a wavelength in a period
distance = rate * time
L = 3*10^8 * period
or
L = 3*10^8 /frequency
for the color look it up in a table of color versus wavelength or frequency
You do not need the energy for this but the energy of a photon is h * frequency where h = Plank constant.