Planck constant

The Planck constant describes how the energy of a photon is related to its frequency.

h=6.63 \times 10^{-34}\,\,Js

We write it with the letter h.

Uses

We use planck’s constant in lots of equations, such as:

• The photoelectric equation - E_{kmax} = hf - \phi
• The equation for the energy of a photon - E = hf
• The equation linking threshold frequency and work function - \phi = hf_0

Units

The units of the Planck constant are joule seconds (Js), which is energy multiplied by time. We can find that out because of the equation E = hf:

• The energy of a photon is measured in joules (J).
• The frequency of a photon is measured in hertz (Hz), which is the same as s^{-1} (because it’s the number of waves per second).
• Rearranging the equation to find the Planck constant gives us h = \frac{E}{f}, which is \frac{J}{s^{-1}}, which is the same as Js.