physics

• Transverse waves


  Particles vibrate PERPENDICULAR to the propagation of the wave
• Longitudinal waves


  Particles vibrate PARALLEL to the propagation of the wave
• Transverse waves vs Longitudinal waves

  • Transverse
  • Longitudinal
• Transverse waves


  Has Crests and Troughs
• Longitudinal waves


  Has Compressions and Rarefactions
• Electromagnetic waves


  Behave both as waves and as particles
• Electromagnetic waves


  • They can refract
  • They can reflect
  • They can interfere
• Electromagnetic waves


  • They can eject an electron from the surface of a metal (photoelectric effect)
  • The wave nature is dominant during the propagation of waves
  • The particle properties dominate during an interaction with other materials
• Electromagnetic waves can travel in a vacuum (without a medium)
• Speed of an EM wave in a vacuum is c = 3x10^8 m/s
• Electromagnetic Spectrum


  • Infrared
  • Ultraviolet
  • Gamma
• Penetrating ability


  • Gamma rays have a greater penetrating ability than x-rays and can penetrate bone/lead that is a few centimetres thick
  • X-rays penetrate through soft tissue, but cannot go through bone
  • Ultraviolet rays of the sun travel through clouds on a cloudy day
  • Infrared rays, which warm your body, cannot travel through clouds
• Properties of EM waves

  • Moves at a constant speed of 3 × 10^8 m/s in a vacuum
  • Electromagnetic waves do not need a medium for propagation
  • Can Reflect, Refract and Interfere
  • EM waves are transverse waves
  • The shorter the wavelength and the higher the frequency, the greater the energy of the EM radiation
• Sunlight is the full spectrum of electromagnetic radiation
• Sunlight is filtered by the earth's atmosphere
• Wave speed (v)


  The distance a wave travels per unit time
• Wavelength (m)


  The distance between two consecutive crests or troughs of a wave
• Frequency (Hz)


  The number of wave cycles that pass a given point per unit of time
• Speed of light (c) = 3.0 x 10^8 m/s
• Infrared rays


  • Wavelength of 3 μm produced by the sun
• Calculating frequency


  1. c = λf

  2. f = c/λ
• Photons


  Discrete energy particles of light
• Photoelectric effect


  Light with a high enough frequency shone on a metal's surface causes the metal to emit electrons
• Calculating photon energy


  1. E = hf

  2. E = hc/λ
• 1. rays have a wavelength of 2 x 10^-10 m
• 1. rays


  • Advantage: CT-scans, security scanners, medical images
  • Disadvantage: Too great an exposure results in cancer and skin damage
• Source of infrared radiation

  • Sun
• Gamma rays have the highest penetrating ability due to their short wavelength and high frequency
• Determining type of EM wave from photon energy


  1. E = hc/λ

  2. Solve for λ to determine the type of EM wave
• Sources of ultraviolet light


  • Sun, ultraviolet light globes
• Why UV light is damaging to eyes

  UV-light with high frequencies (and therefore high energy) enters the eye and can cause permanent damage to the retina
• Why UV light is used in butcheries

  Kills bacteria/microbes, sterilises food
• Why dentists use UV light to harden fillings

  Higher frequencies, more energy, works quicker (less time)
• Propagation of EM waves

  Accelerating charges induce alternating electrical and magnetic fields perpendicular to each other and perpendicular to the direction of propagation
• Main sections of the EM spectrum in order of increasing frequency

  • Radio waves
  • Microwaves
  • Infrared light
  • Visible light
  • Ultraviolet rays
  • X-rays
  • Gamma rays
• EM waves with high penetrating ability


  • X-rays
  • Gamma rays
• Common properties of EM waves

  • Move at a speed of 3 x 10^8 m/s in a vacuum
  • Do not need a material medium to travel through
• Properties that differ in different EM wave sections

  • Wavelength
  • Frequency
  • Penetrating ability
  • Energy of the photons
• Blue light has a shorter wavelength than violet light
• Green light has a higher frequency than red light