MAGNETISM

• what happens when two magnets are brought close together?

  they exert a force on each other
• what is a permanent magnet?


  a magnet that produces its own magnetic field
• what is an induced magnet?


  - a material that becomes a magnet when it is placed in a magnetic field

  - induced magnetism always causes a force of attraction

  - when removed from a magnetic field an induced magnet loses most/all of its magnetism
• what is a magnetic field?


  the region around a magnet where a force acts on another magnet or magnetic material
• what are examples of magnetic materials?


  - iron

  - steel

  - cobalt

  - nickel
• what does the strength of a magnetic field depend on?

  distance from the magnet
• what is the direction of a magnetic field line?

  north-seeking pole to the south-seeking pole of a magnet
• how can you plot the magnetic field pattern of a magnet using a compass?

  move a compass around a magnet and trace its position on some paper
• how is the behavior of a magnetic compass related to evidence that the core of the earth must be magnetic?

  when compasses aren't near a magnet, they always point north because the earth generates its own magnetic field, which shows the core must be magnetic
• what does the strength of the magnetic field around a current-carrying conductor depend on?


  - the current through the wire

  - the distance from the wire
• what is an electromagnet?

  a solenoid with an iron core
• how can the magnetic effect of a current be demonstrated?

  by placing a compass near a wire
• how does a solenoid arrangement increase the magnetic effect of the current?


  the field lines line up so that they are very close and in the same direction, giving a greater magnetic effect
• what happens when two magnets are brought close together?

  they exert a force on each other
• what is the motor effect?


  when a current-carrying conductor placed in a magnetic field and the magnet exert a force on each other
• what is a permanent magnet?


  a magnet that produces its own magnetic field and doesn't lose it
• what is fleming's left hand rule?


  thumb = movement

  first finger = field

  second finger = current
• Give 3 examples of magnets?

  A bar magnet, horseshoe magnet and the earth
• what are the factors that affect the size of the force on the conductor?


  - magnetic flux density

  - size of the current

  - length of the conductor
• what is an induced magnet?


  a magnetic material that becomes a magnet when it is placed in a magnetic field
• what is the basis of an electric motor?

  a coil of wire carrying a current in a magnetic field tends to rotate
• What kind of force do induced magnets always cause?

  Only attraction
• what is the purpose of a split-ring commutator?


  to swap the contact every half-turn to keep the motor rotating in the same direction
• What happens to an induced magnet when it's removed from a magnetic field?

  It loses most or all of its magnetism
• how do loudspeakers work?


  - an ac is sent through a coil of wire attached to the base of a paper cone

  - the coil has each pole on either side so the current causes a force on the pole, which causes the cone to move

  - as the current reverses, the force acts in the opposite direction

  - variations in the current = vibrations to make a sound wave

  
• what is a magnetic field?


  the region around a magnet where it produces a magnetic force that acts on another magnet or magnetic material
• what is the generator effect?


  the induction of a potential difference or current in a wire which is moving relative to a magnetic field, or experiencing a change in magnetic field
• what are examples of magnetic materials?


  - iron

  - cobalt

  - nickel

  - and alloys of these metals e.g steel

  
• what are the factors that affect the size of the induced potential difference/current?


  - stronger magnetic field

  - move more rapidly

  - if shaped into a coil
• Where is the magnetic field the strongest?

  At the poles of the magnet

  
• what are the factors that affect the direction of the induced potential difference/current?


  - the direction of movement changes

  - the poles of the magnet are switched
• How should the direction of a magnetic field line be drawn?


  From the north pole to the south

  
• how does an alternator work?


  as the coil spin, a current is induced which changes directions every half turn using slip rings and brushes to produce alternating current
• how can you plot the magnetic field pattern of a magnet using a compass?


  Because the needle in a compass is a tiny bar magnet, it's North Pole will be south-seeking. so you can move a compass around a magnet and trace the position of the mini bar magnet needle inside on some paper to show what it's magnetic field looks like

  
• how does a dynamo work?


  they use split-ring commutators to swap the connections every half-turn to produce direct current
• How does the behaviour of a compass when not near a magnet prove that the core of the earth must be magnetic?


  when compasses aren't near a magnet, they always point north because the earth generates its own magnetic field similar to a bar magnet's, which shows the core must be magnetic. Also the geographic north must be the magnetic south and vice versa.
• how do microphones work?


  - sound waves hit a flexible diaphragm that is attached to a solenoid wrapped around a magnet

  - the movement of the coil (and so the generated current) depends on the properties of the
• What happens when current begins to flow through a wire?

  It creates a magnetic field of concentric circles perpendicular to the wire

  
• what do transformers do?

  they change the size of the potential difference of an alternating current using primary and secondary coils of wire
• What happens if you change the direction of the current flowing through a wire?

  It changes the direction of the magnetic field