The particle nature of electromagnetic radiation
When we talk of electromagnetic radiation as a particle, we refer to photons, which are packets of energy. The energy of the photon is related to the wavelength of electromagnetic radiation according to: h (called Planck's constant).
- Definition 1: Planck's constant
Planck's constant is a physical constant named after Max Planck.(1)
The energy of a photon can be calculated using the formula: or . Where E is the energy of the photon in joules (J), h is Planck's constant, c is the speed of light, f is the frequency in hertz (Hz) and λ is the wavelength in metres (m).
Example 1: Calculating the energy of a photon I
Calculate the energy of a photon with a frequency of 2 × 1018 Hz.
We use the formula:
Example 2: Calculating the energy of a photon II
What is the energy of an ultraviolet photon with a wavelength of 200 nm?
Determine what is required and how to approach the problem.
We are required to calculate the energy associated with a photon of ultraviolet light with a wavelength of 200 nm.
We can use:
Solve the problem
Exercise 1: Particle nature of EM waves
How is the energy of a photon related to its frequency and wavelength?
The energy of a photon is directly proportional to its frequency and indirectly proportional to its wavelength. We can show this as: , where h is Planck's constant.
Calculate the energy of a photon of EM radiation with a frequency of 1012 Hz.
Determine the energy of a photon of EM radiation with a wavelength of 600 nm.