magnetism & the motor effect

• A magnet always has 2 poles, which are?

  north and south
• What do all magnets produce?

  a magnetic field
• What is a magnetic field?

  a region where other magnets or magnetic materials experience a force
• Example of a drawing of magnetic field lines?


  ...

  
• In what direction do the lines always go?

  from north to south
• What do the lines show?

  which way a force would act on a north pole at that point of the field
• When can you tell the magnetic field is strong?

  the closer together the lines are (closer = stronger)
• When does the field become weaker?

  the further away you get from the magnet
• Where is the magnetic field strongest?

  at the poles of the magnet
• What else is strongest at the poles of a magnet?

  the magnetic forces
• What poles repel each other

  2 like poles
• What does placing the north and south poles of two bar magnets near each other create?

  uniform field between the 2 poles
• Drawing of a uniform field between 2 poles?

  (draw at least 3 field lines, parallel to each other and the same distance apart)

  
• Why can you use a compass to help draw a picture of the field around a magnet?

  a compass needle always lines up with the magnetic field it's in
• Using a compass to help draw a picture of the field around a magnet: step 1?

  put the magnet on paper and draw round it
• Using a compass to help draw a picture of the field around a magnet: step 2?

  place compass on paper near magnet - the needle will point in the direction of the field line at this position
• Using a compass to help draw a picture of the field around a magnet: step 3?

  mark direction of compass needle by drawing 2 dot - one at each end of the needle
• Using a compass to help draw a picture of the field around a magnet: step 4?

  move compass so that the tail end of needle is where the tip of the needle was previously - put a dot at the tip of the needle
• Using a compass to help draw a picture of the field around a magnet: step 5?

  repeat the process of moving the compass and join up marks - end up with a drawing of one field line around the magnet
• Using a compass to help draw a picture of the field around a magnet: step 6?

  repeat the method at different points around the magnet to get several field lines
• Where do compasses always point (when not near a magnet)?

  the Earth's north pole
• Why do compasses always point to the Earth's North Pole?

  The Earth generates its own magnetic field - shows the Earth's core must be magnetic
• Main 3 magnetic elements?

  iron, nickel, cobalt (some alloys and compounds of these metals are also magnetic e.g. steel - contains iron)
• What is the magnetic force between a magnet and a magnetic material like?

  always attractive
• What are permanent magnets?

  produce their own magnetic field all the time (e.g. bar magnets)
• What are induced (or temporary) magnets?

  only produce a magnetic field while they're in another magnetic field
• What happens if you put any magnet into a magnetic field?

  it becomes an induced magnet
• Why does magnetic induction explain why the force between a magnet and magnetic material is always attractive?

  the south pole of the magnet induces a north pole in the material, and vise versa
• What happens to induced magnets when you take away the magnetic field?

  return to normal and stop producing a magnetic field
• How quickly do magnetically 'soft' materials (e.g. pure iron and nickel-iron alloys) lose their magnetism?

  very quickly
• How quickly do magnetically 'hard' materials (e.g. steel) lose their magnetism?

  more slowly
• What are permanent magnets made out of?

  magnetically hard materials
• Uses of magnetic materials: Fridge doors?

  permanent magnetic strip in your fridge door to keep it closed
• Uses of magnetic materials: Cranes?

  use induced electromagnets to attract and move magnetic materials - e.g. moving scrap metal in scrap yard
• Uses of magnetic materials: doorbells?

  use electromagnets that turn on and off rapidly, to repeatedly attract and release an arm which strikes the metal bell to produce a ringing noise
• What does a moving charge (when a current flows through a wire) create?

  a magnetic field around it
• What is the magnetic field around the wire made up of?

  concentric circles perpendicular to the wire (with the wire at the centre)
• Repulsion drawing?

  ...

  
• What does changing the direction of the current change?

  the direction of the magnetic field
• The right hand thumb rule: What does your thumb represent?

  the direction of the current