all about magnets!

• how does electromagnetic induction work

  creating electricity by placing a wire in a moving field which produces current
• electromagnetic induction

  the process of producing electricity from magnetism
• motor effect

  electricity + magnetism -> movement
• generator effect = electromagnetic induction

  movement + magnetism -> electricity
• lenz’s law

  when the current induced opposes the motion
• magnetic field

  a region where a magnetic material experiences a force
• 3 magnetic materials

  iron , nickel , cobalt
• what do magnetic fields show

  The size and direction of magnetic fields
• what direction do magnetic field lines point

  north to south
• what is another name for the strength of the magnetic field

  magnetic flux density
• what is the magnetic field strength measured in?

  teslas (T)
• how do u create a uniform field

  by placing the north and south of two permanent bar magnets near eachother - it creates a uniform field between the two poles
• iron fillings to see magnetic fields

  put the magnet on a piece of paper and scatter the iron fillings on top . The fillings will align themselves with the field lines
• how to use a compass to plot magnetic field lines

  • put the magnet on a piece of paper and place the compass on the paper , next to the magnet . the compass needle will point in the direction of the field lines in this position
  • mark the direction that the compass needle is pointing by making two dots on the paper , one at each end of the needle
  • move the compass so that the tail end of the needle is where the tip of the needle was previously . Repeat this then join up the the marks you have made
  • repeat this method at different points around the magnetic to for several field lines
• like poles repel each other and unlike poles attract
• when a magnet is brought near a magnetic material then that material acts as a magnet . This magnetism has been induced by the original magnet , the closer the two get , the stronger the induced magnet
• permanent vs induced magnets

  induced magnets ( usually ) lose their magnetism once the magnet has been moved away
• an electric current in a material produces a magnetic field around it . The larger the electric current , the stronger the magnetic field
• a magnetic field around a straight , current-carrying wire is made up of concentric circles with the wire in the centre . You can find the direction of the field with the right-hand rule .
• compasses can be used to show that there is a magnetic field and to find the direction of one
• the further away from the wire , the weaker the magnetic field ( shown by the field lines getting further apart )
• if the wire is bent into a loop , the magnetic field will still exist but now it'll look like a toroidal shape . If the wire is coiled tightly enough , the field inside the coil becomes very strong.
• in electromagnetism , the strength of the magnetic field depends on the number of loops of wire , the size of the current flowing through them and how close the core is to the coil .
• electromagnets are made when an iron core is placed within a solenoid ( a long, closely wound coil ). When a current flows through the coil , the magnetic fields produced by all the turns add together to make a much stronger magnetic field than if they were separate .
• when an electric current flows through a solenoid , a magnetic field is produced along its length . This means that if the solenoid is placed over a compass needle , the compass needle will be deflected towards the solenoid .
• in electromagnetic induction , a changing magnetic field causes a potential difference across a conductor which then creates an electric current .
• electromagnets are used in motors , generators , transformers and MRI scanners .
• to make an electromagnet , wrap some insulated copper wire round a piece of iron or steel about 10 times . Connect the ends of the wire to a battery and switch . When the switch is closed , the current flows through the wire and creates a magnetic field around the wire .
• the magnetic field in the centre of a flat circular coil of wire is similar to a bar magnet . There are concentric ellipses ( stretched circles ) of magnetic field lines around the coil
• the magnetic field inside a current-carrying coil is strong and uniform
• the magnetic effect at the ends of the solenoid will increase if:

  • the current in the wire is increased
  • the number of turns ( e.g. the number of coils ) of the wire is increased but the length stays the same
  • the length of the solenoid is decreased but the number of turns stays the same
  • an iron core is added inside the solenoid
• how to create a force on a wire

  when a current-carrying conductor ( e.g. a wire ) is put between magnetic poles , the two magnetic field affect one another . Result is a force on the wire
• to experience the full force , the wire has to be at 90 degrees ( right angle ) to the magnetic field . If the wire runs along the magnetic field , it won’t experience any force at all , angles in between will feel force
• how the force gets stronger

  if either the current or the magnetic field is made stronger
• Changing the direction of either the current or the magnetic field will change the direction of the force
• a good way of showing the direction of a force

  apply a current to a set of rails inside a horseshoe magnet . A bar is placed on the rails which completes the circuit . This generates a force that rolls the bar along the rails .
• why do we use flemmings left hand rule?

  to find the direction of the force of a current-carrying conductor
• how to use flemmings left hand rule

  • point your First finger in the direction of the magnetic Field
  • seCond finger in the direction of the Current
  • thuMb will point in the direction of the force ( Motion )
• equation to calculate the force on a current-carrying conductor (e.g. a wire)


  force on carrying = magnetic x current x length

  conductor (N) flux density (A) (M)

  (T)
• describe how to plot the magnetic field lines of a bar magnet with a compass

  • put the magnet on a piece of paper and put a compass next to it , marketing on the piece of paper the point at which the compass needle is pointing
  • then move the compass so that the tail end of the compass needle is where the tip of the needle was previously and mark against where the needle is pointing
  • repeat this several times and then join up the markings for a complete sketch of a field line around the magnet
  • do this several times for different points around the magnet to get several field lines