Wave Phenomena

• Wavefronts & Rays for transverse waves

  1. The distance between successive wavefronts is equal to the wavelength of the waves

  2. Wave phenomena such as reflection can be shown through rays or the wavefronts
• Wave effects may all be demonstrated using a ripple tank
• Wave Phenomena


  • Wavefronts & Rays
  • Reflection, Refraction & Transmission
  • Diffraction of Waves
  • Interference of Waves
  • Superposition of Waves
  • Young’s Double-Slit Experiment
  • Single-Slit Diffraction (HL)
  • Diffraction Gratings (HL)
• Reflection


  1. Reflection occurs when a wave hits a boundary between two media and does not pass through, but instead bounces back to the original medium

  2. The law of reflection states: The angle of incidence, i = The angle of reflection, r

  3. During reflection, the frequency, wavelength, and speed of the wave do not change
• When waves arrive at a boundary between two materials, they can be: Reflected, Refracted, Transmitted
• Ripple tanks are used as a common experiment to demonstrate diffraction of water waves
• Wavefronts & Rays

  • Waves can be represented graphically in two different ways:
  • Wavefronts - lines joining all the points that oscillate in phase and are perpendicular to the direction of motion (and energy transfer)
  • Rays - lines showing the direction of motion (and energy transfer) of the wave that are perpendicular to the wavefront
• Refraction

  1. Refraction occurs when a wave changes speed and direction at the boundary between two media

  2. If the medium is more dense, the wave slows down. If the medium is less dense, the wave speeds up

  3. When a wave refracts, its speed and wavelength change, but its frequency remains the same
• Transmission

  1. A wave passes through a substance

  2. Refraction is a type of transmission

  3. Transmission is the more general term for a wave appearing on the opposite side of a boundary (the opposite of reflection)

  4. Refraction is specifically the change in direction of a wave when it crosses a boundary between two materials that have a different density

  5. When passing through a material, waves can be partially absorbed

  6. The transmitted wave will have a lower amplitude if some absorption has occurred

  7. During transmission, the frequency or speed of the wave does not change

  8. Reflection, refraction, and transmission occur for all types of waves, both transverse and longitudinal
• The only property of a wave that changes when it's diffracted is its amplitude
• Water waves refracting


  • When they travel from deeper to shallower water
• The extent of diffraction depends on the width of the gap compared to the wavelength of the wave
• When a wave refracts, its speed and wavelength change, but its frequency remains the same
• The wavelength of the waves decreases in the shallower water
• Diffracted waves have less amplitude than incident waves
• This is noticeable by the fact that the color of the wave does not change
• In this case, water is denser than air
• Diffraction is most prominent when the width of the slit is approximately equal to or smaller than the wavelength
• Rearrange wave equation for frequency f


  f = v/λ
• Diffracted waves are most prominent when the wavelength is close to the aperture size
• When light passes from more dense to less dense medium (e.g. glass → air)

  Refracted light has higher speed and longer wavelength than incident light
• When light travels from less optically dense to optically denser medium

  Some energy in the incident light is reflected back, while some is transmitted
• When light passes along the normal (perpendicular)

  Light does not bend at all (i = r)
• When light passes from less dense to more dense medium (e.g. air → glass)

  Light bends towards the normal (i > r)
• Diffracted waves have a wavelength close to the aperture size
• When light crosses the boundary between two media with different optical densities, it refracts
• When light passes from more dense to less dense medium (e.g. glass → air)


  Light bends away from the normal (i < r)
• Wave equation


  v = fλ
• When light travels from less optically dense to optically denser medium

  Both reflection and refraction always occur
• When light passes from less dense to more dense medium (e.g. air → glass)

  Refracted light has lower speed and shorter wavelength than incident light
• Transparent media have different optical densities
• Light has to be reflected from the object to the eye in order for objects to be visible
• Refractive Index

  A measure of the optical density of a transparent medium
• Calculation of refractive index


  n = c/v where n = absolute refractive index of the medium, c = speed of light in vacuum, v = speed of light in the medium
• Fermat's Principle of Light states that light will travel between two points along the path that will take the least amount of time
• The refractive index of air can be assumed to be n = 1
• Snell's Law

  n1/n2 = sin θ2/sin θ1 = v2/v1 where n = absolute refractive index, θ = angles of incidence and refraction, v = speed of light in medium
• When the incident ray is perpendicular to the surface of the boundary, its speed changes, but its direction does not
• The refractive index of any other transparent medium is n > 1 because the speed of light will always be faster than in the medium
• Some of the energy in the incident light is reflected back, while some is transmitted