# Planck's Constant

## Definition - What does Planck's Constant mean?

Planck’s Constant relates the energy of one photon (the smallest possible energy ‘packet’) of electromagnetic waves to the frequency of that wave, and is denoted by h. The energy and frequency in the case of photon energy are directly proportional to each other, and hence Planck’s constant is the constant of proportionality between them.

Planck’s Constant is also known as the Plank Constant.

## Techopedia explains Planck's Constant

The SI (International System) unit for Planck’s constant is approximately equal to 6.626176 x 10^{-34} joule-seconds, whereas in the small-unit metric or centimeter-gram-second (cgs) system it is thought to be approximately equal to 6.626176 x 10^{-27} erg-seconds.

Suppose that E is the energy contained in a photon and it is directly proportional to the frequency f of that electromagnetic wave, then according to the given equation:

Eµf

Or

E = hf

In terms of SI units, E is measured in joules and f (frequency) is measured in hertz, then:

E = (6.626176 × 10^{-34}) f

And hence,

f = E / (6.626176 × 10 – 34)