Properties of EM

• Properties of EM Waves

  • Electromagnetic waves are defined as: Transverse waves that transfer energy from the source of the waves to an absorber
  • All electromagnetic waves share the following properties:
  • They are all transverse
  • They can all travel through a vacuum
  • They all travel at the same speed in a vacuum
  • There are 7 types of electromagnetic waves, which all together form a continuous spectrum called the Electromagnetic spectrum
• Transfer of Energy by EM Waves

  • Electromagnetic (EM) waves carry energy and so can transfer energy from one point to another point
  • This is from a source to an absorber
  • E.g. From the sun to our skin
  • EM waves with a shorter wavelength carry a higher energy
  • This includes UV, X-rays and gamma rays
  • The higher the energy of the EM wave, the more dangerous it is
• Energy Transfer by Microwaves

  • Water molecules absorb certain wavelengths of microwave radiation
  • Therefore, microwave ovens transfer energy from the electronics to heat the food placed inside it
• Energy Transfer by Infrared

  • All hot objects emit infrared radiation
  • The emitted waves can then be absorbed by other objects, warming them up
• Energy Transfers from the Sun

  • The Sun emits several types of EM radiation, including:
  • Visible light waves allow living creatures to see
  • Infrared waves heat up the Earth
  • Ultraviolet waves provide plants with the energy for photosynthesis which they need to grow
• Range of EM Waves

  • The relationship between frequency and wavelength of waves across the Electromagnetic spectrum is
  • The higher the frequency, the shorter the wavelength
  • The lower the frequency, the longer the wavelength
  • This means that radio waves have a lower frequency, and a longer wavelength than UV waves
  • This can be seen from the wave equation

  v = fλ

  • Where:
  • v = speed of the wave in metres per second (m/s)
  • f = frequency of the wave in hertz (Hz)
  • λ = wavelength of the wave in metres (m)
• Wave length and frequency:

  A) Low

  B) High

  C) Large

  D) Low

  
• • The higher the frequency, the higher the energy of electromagnetic radiation
  • Radiation with higher energy is: 
  • Highly ionising
  • Harmful to cells and tissues causing cancer (e.g. UV, X-rays, Gamma rays)
  • Radiation with lower energy is:
  • Useful for communications
  • Less harmful to humans
• The EM Spectrum

  • The electromagnetic spectrum is arranged in a specific order based on the wavelengths or frequencies
  • The main groupings of the continuous electromagnetic (EM) spectrum are:
  • Radio waves
  • Microwaves
  • Infrared
  • Visible (red, orange, yellow, green, blue, indigo, violet)
  • Ultraviolet
  • X-rays
  • Gamma rays
• Electromagnetic light spectrum:

  A) Radio

  B) Micro

  C) Infrared

  D) Visible

  E) Ultraviolet

  F) X

  G) Gamma

  H) Lower

  
• Visible Light- range of wavelengths which are visible to humans (only part of the spectrum detectable by the human eye)

  • However, it only takes up 0.0035% of the whole electromagnetic spectrum
  • In the natural world, many animals, such as birds, bees and certain fish, are able to perceive beyond visible light and can see infra-red and UV wavelengths of light
  • The different colours of waves correspond to different wavelengths:
  • Red has the longest wavelength (and the lowest frequency and energy)
  • Violet has the shortest wavelength (and the highest frequency and energy)
• EM Waves & colour

  A) Increasing

  B) Indigo

  C) Violet

  
• • Wavelength and frequency are inversely proportional, this means that:
  • An increase in wavelength is a decrease in frequency (towards the red end of the spectrum)
  • A decrease in wavelength is an increase in frequency (towards the violet end of the spectrum)
• Light and EM Waves:

  A) Red

  B) Orange

  C) Yellow

  D) Green

  E) Blue

  F) Indigo

  G) Violet