magnatism

• electromagnetic spectrum= family of waves that travel at the same speed and can travel through empty space (a vacuum)
• radiations in electromagnetic spectrum ( biggest to smallest):

  • radio
  • microwave
  • infrared
  • visible
  • ultraviolet
  • x-ray
  • gamma ray
• radio waves= low frequency, long wavelength. they can be used ro transmit information as they are not strongly absorbed by the atmosphere
• bluetooth devices use radio waves to communicate with each other over a short range
• energy from microwave is strongly absorbed by water molecules(which is why they are used for cooking)
• mobile phones use low frequency microwaves to communicate with satellites (microwaves not absorb by atmosphere)
• information can be carried by radio waves, micro waves, infrared waves or visible light
• the shorter the wave length the more information can be carried (shorter waves less likely to be diffracted)
• microphones convert sound into electrical signals (these signals have an alternating current)
• audio signal is carried as an alternating current to the loudspeaker
• infrared is the EM wave that transfers heat. the hotter the object the more infrared radiation emits. its absorbed by skin and can damage or kill cells
• uses of infrared:

  • remote controls
  • infrared scanners (medicine)
  • optical fibres (used in internet)
• visible light is what eyes ate sensetive too
• ultraviolet radiation is ionising and can cause mutations in DNA, leading to cancer
• ozone layer protects the earth as ultraviolet is absorbed by O2
• X-rays are ionising, they are absorbed by bones but are transmitted through soft parts of the body
• gamma rays are on the highest energy and highest frequency part of the EM spectrum, formed by radioactive nuclei the they decay
• permeant magnets produce their own magnetic field, induced magnets only turn into magnets when a current flows through it. force between a permeant magnet and an induced one is always attractive
• magnetic field lines of bar magnet are close together at poles, showing the magnetic field is strongest sea the poles( the closer the field lines the stronger the magnetic field)
• wires have magnetic fields, if you put it between north and south poles the wire would move
• motor effect: when a conductor is carrying a current, it experiences a force in a magnetic field
• Electric motor

  1. Current running in opposite directions on either side of the loop

  2. Loop placed in magnetic field

  3. Force on left side acts upwards, force on right side acts downwards

  4. Loop rotates in clockwise direction
• Loop rotates beyond 90 degrees

  Force on left side acts downwards, force on right side acts upwards, pushing the loop back to 90 degrees
• Split ring commutator

  Split metal ring connected to conducting brushes, allows electric current to pass onto the ring and switch direction when loop passes 90 degrees
• four factors that effect the size of force on a current-carrying conductor placed in a magnetic field

  • angle of conductor
  • strength of magnetic field
  • current size
  • length of conductor
• equation that describes motor effect:

  force(N)= flux density x current in wire x length of wire
• flux density = strength of magnetic field
• electric motor: transferring electrical to kinetic energy

  electromagnetic induction: transferring kinetic to electrical energy
• generator effect: Induced current in a complete circuit when a wire is moved through a magnetic field

  Induced potential :Potential difference induced across the ends of a wire when it is moved through a magnetic field
• Inducing potential difference


  1. Move wire up through magnetic field

  2. Potential difference induced

  3. Stop moving wire

  4. Potential difference lost

  5. Move wire back down

  6. Potential difference induced in reverse direction
• generator effect: Direction of induced current switches when direction of movement switches
• Generator effect: No induced potential or current if wire moves along magnetic field, only if it passes through
• Factors affecting size and direction of induced potential


  • Stronger magnetic field
  • Faster wire movement
  • More turns in coil
• Inducing current in coil


  1. Move magnet in and out of coil

  2. Induced current changes direction when movement direction changes
• Induced current in coil

  Creates own magnetic field that opposes movement of magnet
• transformer = machine for changing the potential difference. step up = increase p.d, step down= reduce p.d
• transformers: the primary coil is connected to a alternating current meaning there is a constantly changing magnetic field around it
• electrical power = voltage x current
• in transformers, two coils are joined to an iron core
• Transformers: p.d across primary coil x current across primary coil = p.d across secondary coil x current across secondary coil