<span>The answer is: ultraviolet
The energy (E) of a photon is directly proportional to its frequency f, by Planck's
formula: E = hf, where h is Planck's constant (6.625 * 10**-34 joule-second).
The frequency is inversely proportional to the wavelength w by: f = c/w, where
c is the speed of light, 3.0 * 10**8 meters per second.
Combine these formulas and we see that the energy is inversely proportional to
the wavelength by: E = hc/w
If the energy is inversely proportional to the wavelength, a photon with twice the
energy has half the wavelength of our 442-nm. photon in this example.
So its wavelength is 221 nm. which is in the ultraviolet range.</span>
