physics P1

• 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
• Wave


  Transmits energy from source to absorber
• Range of frequencies of electromagnetic waves detected by the human eye

  400-700 nanometres
• What can happen when radiation strikes an object

  • Transmitted
  • Reflected
  • Absorbed
• When low energy radiation is absorbed


  It usually causes heating
• When high energy radiation is absorbed


  It can lead to ionisation (the removal of electrons from atoms/molecules)
• Electron arrangement in atoms

  Electrons are found in 'energy levels' or 'shells' at different distances from the nucleus
• 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)
• How atoms become ions

  By losing an outer electron
• Effects of body cells absorbing radiation

  Large amounts can damage cells. Smaller amounts cause mutation, causing cells to divide rapidly, which can lead to cancer.
• Source of gamma rays

  The nuclei of atoms
• What is emitted when electrons in atoms lose energy

  X rays, UV and visible light
• Types of radiation that can cause ionisation

  • Gamma, X-rays and high energy UV (as these have sufficient energy)
• Interaction of atmospheric oxygen with ultraviolet radiation

  Produces ozone
• Function of atmospheric ozone


  Ozone absorbs UV radiation from the sun, protecting the Earth and living organisms from harmful rays
• How infrared radiation interacts with molecules

  It is emitted and absorbed by molecules
• How UV radiation affects body tissue

  UV radiation can cause cancer when skin is exposed to it. It can cause blindness if eyes are overexposed to UV radiation.
• How X-rays affect body tissue

  1. rays are ionising so they can damage or kill cells and cause mutations that could lead to cancer
• How gamma rays affect body tissue

  Gamma rays are even more ionising than X-rays, so they can cause cell mutations (which can lead to cancer) and cell death
• How radio waves are produced (Higher)

  When there is an oscillating current in an electrical circuit
• How radio waves are detected (Higher)


  When the waves cause an oscillating current in a conductor
• Use of radio waves


  Communications, because radio waves are long wavelength and can travel long distances without losing quality
• Use of microwaves


  Cooking, as microwaves are absorbed by and heat fat/water in foods
• Uses of infrared radiation

  Cooking food (as it transfers thermal energy) infrared cameras, short range communication
• Uses of visible radiation


  Illuminating (i.e. seeing) and fibre optics, as they reflect best in glass (other waves have wavelengths that are too long/short)
• Uses of UV radiation

  Sterilisation, as it kills bacteria, energy efficient lamps, as it radiates low heat but high energy, and sun tanning etc.
• Uses of X rays

  Medical imaging and treatment, because they are very high energy and can easily penetrate body tissues
• Uses of gamma rays


  Gamma rays are used in medical treatments, such as radiotherapy in the treatment of cancer
• Main characteristics that separate each EM radiation

  • Wavelength
  • Frequency
  • Energy
• Wavelength


  • From radio waves with the longest wavelength to gamma rays with the shortest
• Frequency


  • From radio waves with the lowest frequency to gamma rays with the highest
  • Our eyes can only detect a limited range of frequencies known as the visible light spectrum
• Energy


  • From radio waves with the lowest wavelength to gamma rays with the highest
• Common characteristics of EM radiation

  • Transverse Waves
  • Do not need particles to move; they are radiation
  • Travel at 3x10ms-1 through a vacuum
  • Other objects may absorb, transmit or reflect EM radiation depending on its wavelength
• EM Radiation transfers energy from source to absorber


  • Microwaves from source to food
  • Sun emits energy to Earth
• Production of EM Radiation

  1. Changes in molecules, atoms and nuclei can generate and absorb radiation over a wide range of frequencies

  2. Gamma rays are emitted from the nuclei of atoms

  3. X-rays, ultraviolet and visible light are generated when electrons in atoms lose energy

  4. Ultraviolet is absorbed by oxygen to produce ozone, which also absorbs ultraviolet, protecting life on Earth

  5. Infrared is emitted and absorbed by molecules
• Ionisation


  • Gamma, X rays and high energy ultraviolet rays, have enough energy to cause ionisation when absorbed by some atoms
  • These radiation have small wavelength, high frequency, and high energy
  • In an atom, electrons are arranged at different distances from the nucleus
  • Arrangements may change with absorption or emission of EM radiation
  • Atoms can become ions by loss of outer electrons
  • Ionisation can cause cells to mutate, potentially causing cancer
  • Radiotherapists, who constantly operate with gamma sources, try to maintain minimal exposure by leaving the room etc.
  • Pilots, flying at high altitudes where there is more UV, have an increased risk of cancer
• Uses of Electromagnetic Radiation

  • Radio Communications
  • Microwaves Cooking
  • Infrared Cooking food, infrared cameras, short range communication, remote
  • Visible Illuminate things
  • UV Sun tanning, energy efficient lamps, sterilisation
  • X ray Medical imaging and treatment
  • Gamma Medical Treatment