Waves in Physics


General notes:

  • A hallmark property of waves is interference
  • In physics, waves are usually associated with the transmission of enegry between different points in space

Three Types of Waves

  1. Mechanical waves
  2. Electromagnetic waves
  3. Matter waves

Mechanical waves

Mechanical waves are propagations of a disturbance thorugh a material medium due to periodic motion of particles that comprise the medium from their mean positions

  • Existence of a medium is essential for propagation of a mechanical wave
    • Propagation occurs due to properties of the medium such as elasticity and inertia
  • Energy and momentum propagate via motion of particles in the medium BUT the overall medium remains in its original position
  • Two main types of mechanical waves:
    1. Transverse waves = the vibration of particles in the medium occurs perpendicular to the direction of wave propagation (e.g., vibration on a string)
    2. Longitudinal waves = the vibration of particles in the medium occurs parallel to the direction of wave propagation (e.g., oscillations in a spring, internal water waves, tsunamis, sound waves etc.)

Electromagnetic waves

Electromagnetic waves = periodic distortions in electric and magnetic fields

  • Two components: an electric component and a magnetic component
  • Initiated when charged particles (e.g., electrons) begin vibrating due to various forces acting on them
    • The vibration of these charged particles then results in the emission of energy called electromagnetic radiation
  • Importantly, electromagnetic waves do NOT require a medium to travel through
    • As far as we know, this property is unique to electromagnetic waves
  • Other properties:
    • Travel at the speed of light ($3 \cdot 10^8 \mathrm{m/s}$) in a vacuum
    • Can be polarized
    • Transverse in nature
      • Propagate out from their source (i.e., the vibrating particles)
      • Oscillations of waves occur perpendicular to the direction they are propagating/traveling
        • Furthermore, in the case of electromagnetic waves, oscillations in the magnetic component occur in a direction perpendicular to oscillations in the electric componet
    • No medium required
    • All EM waves have momentum (thus, they have kinetic energy)

Matter waves

Matter waves (or, de Broglie waves) = depict the wave-like properties of all matter

  • Assumes wave-particle duality for all matter
  • Frequency of these waves depends on their kinetic energy
  • Momentum is not directly (or, inversely) proportional to position of the wave

Miscellaneously-classed waves

Surface waves (or, Rayleigh waves) = can have mechanical or electromagntic nature

Standing waves = a wave that remains constant


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