The Plank constant enables an equation to be formulated for a conversion between hertz (Hz), a unit of frequency, and the joule (J) , a unit of energy.

- Mathematical equations are constructed from expressions some of which are numerical constants (numbers) which do not change. Variables, on the other hand, are expressions, the value of which can change.
- The equation, Energy = Planck Constant x Frequency, allows the quantity of energy associated with electromagnetic radiation to be calculated if the frequency is known.

https://en.wikipedia.org/wiki/Planck_constant