# Photon kinetic energy

How is a photon's energy determine in relation to it's wavelength and frequency?
For example, 20hz vs. 400ghz electromagnetic waves.

How is a photon's energy determine in relation to it's wavelength and frequency?
For example, 20hz vs. 400ghz electromagnetic waves.
The energy of a photon, E (which can be considered as all kinetic energy since the proper energy = E0 = 0 and E = K + E0 = K), is related to the photon's frequency, f, by E = hf where h = Planck's constant = 6.626068 × 10-34m2kg/s.

Pete

can E=1/2mv^2 be applied to photons ever?
or E=mc^2

The proper relativistic equation is
:$$E^2 = p^2c^2 + m^2 c^4$$, which works just fine for photons when $$m = 0$$.

For ordinary particles, one can Taylor expand $$E = \sqrt{p^2c^2 + m^2 c^4}$$ to get a non-relativistic equation most people use... but for photons, you can't do this, and $$E = pc$$ simply.

According to de Broglie, $$p = h \nu$$, of course.

can E=1/2mv^2 be applied to photons ever?
or E=mc^2
No.

Pete