Developing Theories of EM Radiation (AQA A Level Physics): Revision Note

Developing theories of EM radiation

Isaac Newton (1672)

• Newton proposed that visible light is a stream of microscopic particles called corpuscles

• However, these corpuscles could not explain interference or diffraction effects, therefore, the view of light as a wave was adopted instead

Christiaan Huygens (1678)

• Huygens came up with the original Wave Theory of Light to explain the phenomena of diffraction and refraction

• This theory describes light as a series of wavefronts on which every point is a source of waves that spread out and travel at the same speed as the source wave

  • These are known as Huygens' wavelets

Thomas Young (1801)

• Young devised the famous double-slit experiment

• This provided experimental proof that light is a wave that can undergo constructive and destructive interference

James Clerk Maxwell (1862)

• Maxwell showed that electric and magnetic fields obeyed the wave equation

  • This means that light was simply waves made up of electric and magnetic fields travelling perpendicular to one another

• Later, Maxwell and Hertz discovered the full electromagnetic spectrum

Albert Einstein (1905)

• Einstein discovered that light behaves as a particle, as demonstrated by the photoelectric effect

• He described light in terms of packets of energy called photons

• Later the scientific community came to understand that light behaves both like a wave and a particle

  • This is known as wave-particle duality