Paper 2 - P8-P13

• All waves transfer energy from one place to another, but they do not transfer matter.
• Transverse waves:

  The wave moves up and down which scientists call oscillations. In tranverse waves the oscillations are perpendicular to the direction of the energy transfer.
• Longitudinal waves:

  In a longitudinal wave, the oscillations are parallel to the direction of energy transfer.
• All longitudinal waves require a medium to travel e.g. air, a liquid or a solid.
• Not all transverse waves require a medium.
• The amplitude of a wave is the maximum displacement of a point on a wave away from its undisturbed position.
• The wavelength of a wave is the distance from a point on one wave to the equivalent point on the adjacent wave.
• Wave Structure:

  A) amplitude

  B) wavelength

  C) wave

  D) peak

  E) trough

  
• Longitudinal Wave:

  A) Rarefraction

  B) Travel

  C) Compression

  
• Wavelength can be measured on longitudinal waves by measuring from one compression to the other or from one rarefraction to the other rarefraction.
• The frequency is the number of waves passing a point each point each second. The unit of frequency is hertz (Hz).
• The period is the time for one wave to pass a point.
• The wave speed is the speed at which the wave moves through the medium (ie. the speed at which energy is transferred).
• Electromagnetic waves are transverse waves. They transfer energy from the source of the waves to an absorber.
• Each colour of light has a different wavelength and frequency.
• On the red end of the spectrum, the waves have a lower frequency and a longer wavelength.
• On the violet end of the spectrum, the waves have a higher frequency and a shorter wavelength.
• Visible light is the only part of the electromagnetic spectrum that can be detected by the human eye.
• The frequency increases from radio waves to gamma rays.
• The wavelength decreases from radio waves to gamma rays.
• The electromagnetic spectrum is a continuous spectrum. This means that the cut-off point between one type of wave and another is not always clear.
• Electromagnetic waves do not need a medium to travel in.
• Electromagnetic waves can travel through a vacuum (e.g. in space).
• All electromagnetic waves travel at the same speed in a vacuum. That speed is 3x10^8 m/s.
• Different materials absorb, transmit or reflect electromagnetic waves.
• Microwaves are absorbed by foods which contain water molecules.
• Microwaves are reflected by metals.
• Light waves are absorbed by black surfaces and reflected from shiny, metallic surfaces.
• Refraction: waves can change when they change speed, moving from one medium to another.
• When light from air into glass, the velocity of light decreases (the light waves slow down).
• This causes the direction of the waves to change.
• When the waves pass from the glass back to the air, their velocity increases.
• Refraction can happen when any wave changes speed as it passes from one medium to another.
• If the waves enter or leave the medium at right angles to the surface (along the normal), then they do not change direction.
• The wavefront is an imaginary line that connects all the same points in a set of waves.
• When electromagnetic waves are generated or absorbed, changes take place in atoms or in the nuclei of atoms.
• When we heat atoms, we cause electrons to move from one energy level to a higher one. When this electron energy level, it generate an electromagnetic wave (light). A change in the atom has generated on electromagnetic wave.
• Gamma rays can be emitted from the nucleus of radioactive atoms. Once the gamma ray has been emitted, the nucleys has less energy than it had at the start.
• When electromagnetic waves are absotbed, that can also cause changes to atoms e.g. electrons can change energy levels.
• Electromagnetic waves can be emitted and absorbed over a wide frequency range from radiowaves to gamma rays.