WAVES

WAVES

Key Terms
1. Amplitude (metres,m): distance between the rest postition and the peak or trough.
2. Wavelength (meters,m): distance between a point on one wave to the SAME point on the next wave
3. Frequency (Hertz, Hz): the number of wave crests passing a fixed point in a second
Types of Waves
1. Transverse: oscillations (vibrations) are perpendicualr to the direction that the energy travels
  1. e.g Electromagnetic waves
2. Longditudinal: oscillations (vibrations) are parallel to the direction that the energy travels
  1. e.g Sound waves
3. Mechanical: require a medium to travel, cannot occur in a vacuum
  1. e.g Sound waves
4. Electromagnetic: can occur in a vacuum. Are always transverse
  1. e.g light and transverse
5. Plane: Waves that form straight lines.
  1. Can be formed by oscillating a straight bar onto the surface of water.
6. Circular: Waves that are circular in shape.
  1. Can be formed by oscillating a single point onto the surface of water.
Wave Speed Equation
1. wavespeed = frequency x wavelength
  1. m/s = Hz x m
    1. v = f x λ
      1. f = v/λ
      2. λ = v/f
2. 1. Calculate the speed of a wave with a frequency of 3Hz and a wavelength of 2m
  1. 3Hz x 2m = wavespeed
    1. 3Hz x 2m = 6 m/s
Reflection
1. Angle of incidence = Angle of reflection
  1. (i)
  2. (r)
2. In a plane mirror:
  1. Image formed in a plane mirror is
    1. laterally inverted (left and right are switched)
    2. upright (top and bottom are not switched)
    3. virtual (cannot be projected onto a screen)
Diffraction
1. Diffraction is the spreading out of waves when they pass through a gap or round the edge of an obstacle.
  1. Diffraction is at most when the wavelength is the same length as the obstacle.
  2. The signal from a TV transmitter mast is carried by radio waves. If there are hills between a TV reciever and the transmitter mast, the signal may not reach the reciever. The radio waves passing the top of the hill are diffracted by the hill but the do not spread enough behind the hill.
Sound
1. The frequency range of the normal human ears is from about 20Hz to about 20000Hz
2. Sound waves are vibrations that travel through a medium (substance). They cannot travel through a vacuum.
3. Echoes are due to sound waves reflected from a smooth, hard surface
Electromagnetic waves
1. Key Characteristics:
  1. All electromagnetic waves can travel in a vacuum
  2. All electromagnetic waves travel at 3 x 10^8 m/s in a vacuum
  3. All electromagnetic waves are transverse waves
2. Spectrum:
  1. Radiowaves
  2. Microwaves
  3. Infrared
  4. Visible Light
    1. Red
    2. Orange
    3. Yellow
    4. Green
    5. Blue
  5. Ultraviolet
  6. X-rays
  7. Gamma rays
  8. Wavelength
  9. Frequency
  10. Energy
3. Uses
  1. Light: cameras - film and digital. To see. Optical fibres
  2. Infrared: optical fibres. Infrared scanners (medical)
  3. Microwaves: mobile phones satellite TV
  4. Communication
    1. The shorter the wavelength
      1. The more information they carry
      2. The shorter their range (due to absorption by the atmopshere)
      3. The less they diffract and spread out
  5. Satellite TV: Microwaves can pass through tthe atmosphere and diffract less than radiowaves. They also carry a lot more information
  6. Terrestrial TV: Short radiowaves still carry a lot of information and do not need to pass though tthe atmoshpere
  7. Local Radio: Radiowaves. Signals do not need to travel far or carry much information. (1m < λ< 100m)
  8. International Radio: Radiowaves. Do not need to carry much information but need a larger range. (λ>100m)
  9. Optical Fibres
    1. Are thin transparent fibres that are used to transmit signals by light nd infrared radiation.
    2. The light rays can't escape from the fibre, making them more secure.
    3. When they reach the surface of the fibre, they are reflected back into the fibre.
    4. Optical fibres can carry much more information than radiowaves and microwaves.
The Big Bang Theory
1. Doppler Effect
  1. The change in an observed wavelength or frequency of a wave due to the motion of the source of the wave
    1. Water: duck swimming on surface of pond
    2. Sound: screaming person running past observer
      1. Observer hears sounds with shorter wavelength, higher frequency
      2. Observer hears sounds with a longer wavelength, lower frequency
2. Red Shift
  1. White light can be dispersed through refraction into the different colours of the spectrum.
  2. The colour spectrum shows patterns of black lines called absorption lines. This is due to some wavelengths of light being absorbed by elements such as hydorgen
  3. An object that is moving away from us shows this pattern of lines moving towards the red end of the spectrum.
    1. Edwin Hubble discovered that:
      1. 1. Light from a distant galaxy is red-shifted. Distant galaxies are moving away from us.
      2. 2. The further away the galaxy, the greater the red-shift. The further away the galaxy, the faster it is moving away.
3. The universe is expanding after exploding from a single initial point
  1. Evidence:
    1. 1. Red Shift: indicates that distant galaxies are moving away and that the universe is expanding. If it is expanding it must have originated as something smaller. i.e a single initial point
    2. 2. Cosmic Microwave Background Radiation (CMBR): If there was a huge explosion during the Big Bang there would be traces of this explosion throughout the universe. Microwave radiation can be detected from every direction in space. It is thought thst this was originally gamma radiation from the Big Bang. As the universe has expanded these waves have streched to longer wavelength microwaves. It is theorised that they will eventually stretch to become radio waves
4. Space, time and matter were created in the Big Bang
5. Future of the universe
  1. Big Yawn
  2. Big Crunch

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