Planck's constant, symbolized
h, relates the energy in one
quantum (
photon) of electromagnetic radiation to the
frequency of that radiation. In the International System of units (
SI), the constant is equal to approximately 6.626176 x 10
-34 joule-seconds. In the centimeter-gram-second (
cgs
) or small-unit metric system, it is equal to approximately 6.626176 x 10
-27 erg-seconds.
The energy E contained in a photon, which represents the smallest possible 'packet' of energy in an electromagnetic wave, is directly proportional to the frequency f according to the following equation:
E = hf
If E is given in joules and f is given in hertz (the unit measure of frequency), then:
E = (6.626176 x 10-34) f
and conversely:
f = E / (6.626176 x 10-34)
Also see electromagnetic field, energy, frequency, SI, and Table of Physical Units and Constants.
This was last updated in April 2002
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