Topic 5

• Total internal reflection


  • When light is completely reflected back at a boundary between two mediums
  • It occurs when light meets a less dense medium at an angle of incidence larger than the critical angle
• Critical angle

  The angle of incidence which causes the angle of reflection to be 90 degrees
• Colour of visible light


  Determined by the wavelength and frequency of the light waves
• Blue light has the highest frequency of visible light
• Red light has the largest wavelength of visible light
• Specular reflection


  Rays are reflected from a smooth surface in a single direction
• Diffuse reflection

  Reflection from a rough surface which causes scattering
• How a red colour filter works

  1. Absorbs all wavelengths of light other than those in the red range of the spectrum

  2. Only red light passes through the filter
• Opaque


  Not see-through
• What governs the colour of an opaque object

  1. Different objects reflect different wavelengths of light by different amounts

  2. The wavelengths that are most strongly reflected determine the colour
• Any wavelengths that aren't reflected by an opaque object are absorbed
• If all wavelengths are reflected by equal amounts, the object appears white
• If all wavelengths are absorbed, the object appears black
• What do all bodies (objects) emit and absorb?

  Infrared radiation
• As temperature increases

  The quantity of infrared radiation emitted by an object increases
• As temperature increases


  The type of radiation emitted by an object becomes shorter wavelength (e.g. X-rays and gamma rays)
• What is required for a body to be at a constant temperature? (Higher)

  The body would need to emit radiation at the same rate it absorbs it - it needs to radiate at the same average power that it absorbs
• Intensity

  The power transferred per unit area; it is a measure of the energy transferred by a wave
• If the average power that an object radiates is less than it absorbs

  The temperature of the object will decrease
• For a body increasing in temperature

  The body is absorbing radiation faster than it is emitting it
• Factors that affect the temperature of the Earth (Higher)

  • The Earth's rate of absorption and emission of radiation
  • The amount of reflection of radiation into space
• How does the Earth's atmosphere affect radiation? (Higher)

  The atmosphere largely absorbs or reflects radiation from the sun, preventing it from reaching Earth. Some radiation, however, is allowed to pass through and warms the earth
• What happens to the radiation emitted from the Earth? (Higher)

  It is absorbed and re-emitted in all directions by greenhouse gases, resulting in the greenhouse effect which warms the earth
• Electromagnetic waves

  Transverse waves
• Electromagnetic waves transfer energy (not matter)
• Electromagnetic spectrum

  A continuous spectrum
• Order of the electromagnetic spectrum in order of increasing wavelength

  • Gamma
  • X Ray
  • UV
  • Visible
  • Infrared
  • Microwaves
  • Radio
• Highest frequency electromagnetic wave

  Gamma waves
• Highest energy electromagnetic wave

  Gamma waves
• Properties shared by all electromagnetic waves

  • They are all transverse waves
  • They all travel at the same speed (3x10⁸ m/s)
  • They can travel through a vacuum
• Range of frequencies of electromagnetic waves detected by the human eye

  400-700 nanometres
• Electromagnetic waves all travel at the same speed in a vacuum and in air
• What can happen when radiation strikes an object

  • Transmitted
  • Reflected
  • Absorbed
• Oscillations in an electrical circuit

  Can produce radio waves
• How radio waves create an alternating current in a circuit

  Radio waves are absorbed, they can induce oscillations in a circuit with the same frequency as the waves themselves
• Gamma rays


  Originate from changes in the nuclei of atoms
• Ultraviolet waves

  • Can cause the skin to age prematurely
  • Can increase the risk of developing skin cancer
• 1. rays and Gamma rays

  • They are ionising radiation so can cause mutations in genes
  • They can lead to increased risk of developing various cancers
• Infrared rays

  • Can cause burns to skin/tissue
• How electromagnetic radiation affects electron arrangement in atoms

  Absorption or emission of electromagnetic radiation can cause electron arrangement to change (It can remove electrons from the atom or move electrons further from the nucleus)