Waves and Radiation

Waves and Radiation

1. Types of waves

   • Transverse
     • The energy of a transverse wave travels at a right angle tot he direction it is traveling in. It doesn't need particles to move. An example of a transverse wave is a water wave
   • Longitudinal
     • The energy of a longitudinal wave travels in the same direction that it is traveling in. It needs particles to move. An example of a longitudinal wave is sound.

2. Speed

   • Sound
     • 340 m/s (in air)
   • Light
     • 300,000,000 m/s (in air / vacume)
     • 200,000,000 m/s (in an Optical fiber)
   • electromagnetic spectrum
     • 300,000,000 m/s (through a vacume)

3. Wave

   • Frequency
     • Frequency is defined as the number of waves per second
     • Frequency is measured in Hertz (Hz)
   • Period
     • Period Is the number of waves to pass (a certain point)

4. Angles

   • Reflection
     • Angle of incident = Angle of reflection
   • Refraction
     • When a ray of light Travels from thinner material (air) to a more dense material (glass), the ray of light will refract (bend) towards the normal.
     • The angle of incidence is greater then the angle of refraction
   • Total internal reflection
     • At a certain angle (critical angle) the light doesn't refract out. It is trapped inside (total internal reflection). This is what occurs in optical fibers.
       • optical fibers
         • How light travels through an optical fiber

5. lenses

   • Convex (Converging)
     • used to correct long sight
   • Concave (diverging)
     • Used to correct short sight
   • power
     • Have a negative focal length and power
     • Have a positive focal length and power

6. Radiation

   • Backgrond
     • The air around us is slightly radioactive - we are exposed to this background radiation 24 hours a day.
     • Sources of background Radiation includes :
       • Cosmic rays from outer space
       • Rocks such as granite
       • hospital waste from cancer treatment
       • nuclear weapons tests
       • leaks from nuclear power stations
   • Radioactive decay
     • Radioactivity is the decay of ionising radiation
     • The three main types of radiation are Alpha, Beta and Gamma
   • How to tell radioactive sources apart
     • Alpha
       • Alpha source can be reconised because it can not travel through papper
     • Beta
       • Beta source can be recognised because it can travel through paper but it can not travel through aluinium
     • Gamma
       • Gamma source can be reconised because it can travel through paper, aluminium and lead but lead has the biggest effect on gamma rays.
   • safety
     • Don't touch with your hands use tongs
     • Spend a limited amount of time around the source
     • Don't stand in line with the source
     • Don't point the source at anybody
     • Kept in a lead line box
   • Ionisation of Atoms
     • Radioactivity can knock electrons out of atoms. this is known as ionisation.
     • Radioactivity Can ionise atoms in the cells of the human body - This can kill the cells or change their nature - The cell might grow in a different way to what they should or might change into cancer cells.
       • Because radioactivity kills living cells, it is used to sterilise surgical instrument - the bacteria cells are killed
   • Activity
     • Activity is the number of decays per second
   • Half life
     • The half life is the time taken for the activity of a sample to drop by half

7. Electromagnetic spectrum

   • Visable light
     • Violet refracts the most
     • Red refracts the least
     • Primary colours
       • Red
       • Blue
       • Green
     • Secondary colours
       • yellow
       • Magenta
       • Cyan

8. modulation

   • Amplitude (AM)
     • To transmit sound by radio a high frequency carrier wave is added to the sound (audio) signal.
     • This can make the amplitude of the carrier wave change. (it has the same frequency but varying amplitude)
   • Frequency (FM)
     • In this case the amplitude of the carrier wave stays the same but the sound signal it carries now varies the frequency

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