5.1: Discovery of Electromagnetic Waves

• Electromagnetic Waves


  are waves that are made of electric and magnetic field components. They do not need a medium to propagate, hence, they can travel through space.
• Light exhibits different behaviors when it encounters a medium
• Reflection


  is the bouncing back of light when it reaches the boundary between two media, and the light stays in the original medium
• Refraction


  is the bending of light as it travels from one medium to the other
• Dispersion


  is the separation of light into bands of colors: red, orange, yellow, green, blue, and violet
• v = λf

  speed at which a wave propagates
• 3.0 × 10^8 m/s


  speed of light in a vacuum
• People have been studying light since antiquity, even before the discovery of light’s nature as an electromagnetic wave.
• Euclid of Alexandria


  postulated that light “coming from the eye” travels in a straight line. He also worked on the reflection of light.
• Claudius Ptolemy ((c. 100 CE – c. 170 CE)


  famous for his geocentric model of the universe, studied the refraction of light and color phenomena.
• James Bradley


  y used the apparent change in the position of stars as Earth revolves around the Sun to measure the speed of light. The value he obtained was 3.0 × 10^8 m/s, which is within 1% of the current estimate
• There were earlier attempts in measuring the speed of light by other scientists, including Galileo Galilei and Ole Roemer but their methods did not yield any useful results
• The current value is at 299 910 000 m/s, which can still be approximated as 3.0 × 10^8 m/s.
• Two competing models emerged to explain the behavior of light in the 1600s, the particle model and the wave model.
• According to the particle model

  light is made of a stream of particles traveling in a straight path
• Isaac Newton (1642–1727)


  is among the leading proponents of the particle model
• Reflection is explained as the bouncing of light on a surface, much like a bouncing ball
• Refraction is explained by the presence of a certain force at the interface of two media; the nature of this force is left ambiguous
• According to Newton, since light travels in a straight line, it must be a particle because waves are known to bend through obstacles


  Example: sounds can be heard through walls since sound waves bend around them
• After various scientists showed the possibility of the particle model of light, Albert Einstein offered an explanation in 1905.
• Albert Einstein


  He suggested that light, at least in some instances, should be considered to be composed of small packets of energy or particles called photons.
• Albert Einstein added that


  the energy of each particle was proportional to the frequency of the electromagnetic radiation that it was a part of
• On the other hand, the wave model tells us that light is an energy-carrying disturbance or vibration similar to sound and water ripples.
• Christiaan Huygens (1629-1695)


  worked on a mathematical theory of the wave nature of light.
• Mathematical Theory of the Wave Nature of Light


  Reflection is explained as the bouncing of light waves on a material it cannot pass through, similar to the echo of sound and ocean waves bouncing on a steep cliff while refraction of light is the slowing down of the waves as light moves to a different medium.
• The wave model also predicted that light is capable of interference, or waves amplifying or cancelling each other.
• The current consensus among scientists is that electromagnetic waves are both wave and particle; both models are useful in different situations.
• The wave model is useful in developing radio wave transmission for telecommunications while the particle model is useful in developing photovoltaic cells for generation of electricity.
• James Clerk Maxwell (1831-1879)


  came up with the theory of electromagnetic waves. He proposed the idea that electric and magnetic fields induce one another as they propagate. As an electromagnetic wave, it is believed to be vapable of traveling through the vacuum.
• Maxwell hypothesized that light is an electromagnetic wave because its speed matched the known speed of light.
• Heinrich Hertz (1857-1894) 


  using Maxwell's theories, discovered radio waves by building devices that can produce and receive them. He determined that radio waves also travel at 3.0 × 10^8 m/s, and exhibit wave properties similar to that of light. This established that both radio waves and visible light are electromagnetic waves.