⇒ In the early 20th Century, Max Planck developed his quantum theory

⇒ According to Planck's quantum theory, different atoms and molecules can emit or absorb energy in discrete quantities only

• The discrete quantities of energy (quanta) absorbed or emitted is essentially just a small packet (a sort of short burst) of electromagnetic waves, known as a photon
• In short, photons are quanta of electromagnetic energy

⇒ The energy of the radiation absorbed or emitted is directly proportional to the frequency of the radiation.

⇒ Einstein imagined photons to be like flying needles

⇒ The equation that explains this is: E = hf

• E = Energy of the radiation
• F = Frequency of the radiation absorbed or emitted
• h = A constant, now called the Planck constant (the value of Planck's constant is 6.626×10^–34 Js)

⇒ Also see our notes on:

• Introduction to Particles and Nuclides
• The Building Blocks
• Stable/Unstable Nuclei
• Nuclear Radiation
• Nuclear Equations
• Antiparticles