The Electromagnetic Spectrum

• Radio Signals

  • Radio waves can be caused by oscillations in electrical circuits, i.e. an alternating current.
  • The frequency of the radio wave produced matches the frequency of the electrical oscillation. This is how a radio signal is produced.
  • When radio waves are absorbed by a conductor they may create an alternating current with the same frequency as the radio wave, this is how the signal is received.
  • When this oscillation is induced in an electrical circuit it creates an electrical signal that matches the wave.
• Ionising radiation:

  • Ultraviolet / X-Ray / gamma rays
  • UV -cause skin to age prematurely and increase the risk of skin cancer
  • X-rays and gamma rays are ionising -damage cell by ionising atoms, if absorbed by nucleus can cause gene mutation and cancer
• If Irradiated...

  • cells can mutate causing cancer
  • cells die leading to burns, sickness and death
• Requires Prac: Investigate how the amount of infrared radiation absorbed or radiated by a surface depends on the nature of that surface.
• RP Method:

  Sample Method

  1. Take four boiling tubes each painted a different colour: matt black, gloss black, white and silvered.
  2. Pour hot water into each boiling tube.
  3. Measure and record the start temperature of each tube.
  4. Measure the temperature of each tube every minute for 10 min.

  The tube that cools fastest, emits infrared energy quickest.
• RP: considerations mistakes and errors

  • A common error in this experiment is not having the boiling tubes at the same temperature at the start - a hotter tube will cool quicker initially, which can affect results.
  • Evaporation from the surface of the water can cause cooling too, which will affect the results. To minimise this, block the top of each tube with a bung or a plug of cotton wool.
• RP: Hazards

  • The main hazard is being burned when pouring the hot water and when handling the hot tubes. Using a test tube rack to hold the tubes minimises the need to touch the tubes and means hands can be kept clear when pouring the water into them.
• RP: Variables

  The independent variable is the colour of the boiling tube.

  • The dependent variable is the temperature.
  • Control variables include volume of water, start temperature and environmental conditions.