P4.1 + P4.2 (magnetism)

• what can you use to explain the movement of magnets?

  Magnetic field lines
• what do field lines represent?

  magnetic flux
• what is magnetic flux density?

  The number of field lines passing through a particular area
• what is another term for magnetic flux density?

  Magnetic field strength
• what does the density of the field lines show you?

  the strength of the magnetic field
• what is another word for a magnetic region in a material?

  domain
• what happens when the magnetic field is removed in soft/hard magnetic materials?

  soft: the domains return to their original direction

  hard: the domains continue to be lined up
• where do magnets always line up?

  So that one end is pointing towards the magnetic north pole, this is not the same as the north pole
• where will a compass point?

  Towards the magnetic north pole, it is a north seeking pole
• What is a dip?

  The angle between the field lines and a line horizontal to the surface of the earth, it is 90° at the north and south magnetic poles and zero at the magnetic equator, the uk has a dip of about 70°
• what did Oersted discover in 1820?

  there is a magnetic field around a current carrying wire
• what did oersted discover about direction of current in relation to field lines?

  if current was coming towards you, the field lines were anticlockwise
• how do you use the right hand grip rule?

  The thumb represent direction of current and the fingers represent the field lines
• what does the strength of the field around a wire depend on?

  -the magnitude of the current : a bigger current = a stronger field

  -the distance from the wire : nearer the wire = a stronger field
• what is the strength of a magnetic field measured in?


  teslas, a very strong permanent magnet has a magnetic field of about 1T but a normal current carrying wire would have around 0.1 mT
• what do many parallel loops of wire create?

  A coil or a solenoid, adding together many fields produces a much stronger field than that of a single wire
• what does the field around a solenoid produce?

  An induced magnet
• how can you make a solenoid stronger?

  Putting a magnetic material inside the core
• what happens when you put two fields together?

  If they are in the same direction they will add up but if they are in opposite directions they will cancel out
• what is the equation for the force on a conductor?

  Force on a conductor (at right angles to a magnetic field) carrying a current (N) = magnetic flux density (T) x current (A) x length (m)
• How could you make a very simple motor?

  Making a piece of wire into a loop and placing the loop into a magnetic field, when you connect the wire to a battery,the current flows and one side of the wire goes up while the other goes down
• how can you ensure a motor will always have current coming in through the right and out through the left?

  Split ring commutator
• what does a split ring commutator do?


  Enables current to flow the same way from the battery and change to different halves of the coil as it spins
• how can you change the speed of a motor?

  by changing :

  The magnitude of current flowing in the coil

  The strength of the magnetic field

  The number of coils of wire

  The length of the coil
• how can you induce a potential difference?

  By moving a conductor in a magnetic field or making a field change around a conductor
• what is the 1 rule for inducing a potential difference?

  Field lines have to be cut
• what factors does induced potential difference depend on?

  The length of wire in the field and the rate at which you cut the field lines
• how do you increase an induced potential difference?

  Moving the wire faster, using a stronger magnetic field and using more wire (loops and coils)
• What does an alternator (alternating current generator) use to induce a potential difference?

  the coil of wire that spins between the poles of a magnet, it is the same as moving a magnet in and out
• why are slip rings used in alternators?

  brushes brush against them so the voltmeter is always connected but the coil doesnt get tangled
• describe how a dynamo works

  It is a direct current generator and the potential difference that drives a current does not change direction, you can use the same arrangement that is used for a motor
• what do dynamos and alternators use?

  dynamos: use split ring commutators and produce direct current (dc)

  alternators: use slip ring commutators and produce alternating current(ac)
• how can output in alternators and dynamos be increased?

  Using a stronger magnetic field

  Using more turns on the coil

  Spinning the coil faster
• what are transformers used for?

  To increase or decrease potential difference, it is induced when the field lines cutting a coil are changed
• give 3 ways that you can change the field lines that cut the coil

  Moving the magnet or the coil, using another coil and turning the current on and off or using another coil that has an alternating current in it
• how can you use current to change the number of field lines?

  If you turn the coil on and off then you change the number of field lines cutting the other coils
• how can you use alternating current to change the number of field lines?

  The current will flow one way and then the other way so the field lines constantly change
• how could you make a transformer?

  Making a loop of iron with 2 coils, it is a transformer because the magnetic field is trapped inside the iron core
• how do transformers work?

  An alternating potential difference across the primary coil produces an alternating current in the primary coil

  An alternating current in the primary coil produces a magnetic field in the iron core that is always changing

  This induces a changing potential difference in the secondary coil
• what is the equation used in transformers?

  Potential difference across primary coil(v) divided by potential difference across secondary coil(v) is equal to number of turns in primary coil divided by number of turns in secondary coil