12

• 12.1 Recall that unlike magnetic poles ________ and like magnetic poles

  __________

  attract

  repel
• Name some magnetic materials

  Iron, steel, nickel and cobalt
• 12.2 Describe the uses of permanent and temporary magnetic

  materials

  Permanent magnets are used in computers, motors, cars, generators, headphones, speakers, sensors, etc. Magnetic strips and fridge magnets are also common uses of permanent magnets.

  
  

  Temporary magnets can be useful in applications that generate a temporary magnetic field and require a magnetic response for the duration of the field.
• 12.3 Explain the difference between permanent and induced magnets

  A permanent magnet produces its own magnetic field. An induced magnet is a material that becomes a magnet when it is placed in a magnetic field. (Induced magnetism always causes a force of attraction.)
• 12.4 Describe the shape and direction of the magnetic field for a uniform field, and relate the strength of the field to the concentration of lines

  A uniform magnetic field is one that has the same strength and direction at all points

  To show that the magnetic field has the same strength at all points there must be equal spacing between all magnetic field lines

  To show that the magnetic field is acting in the same direction at all points there must be an arrow on each magnetic field line going from the north pole to the south pole

  If the magnetic field lines are close together then the magnetic field will be strong

  If the magnetic field lines are far apart then the magnetic field will be weak
• 12.4 Describe the shape and direction of the magnetic field around

  bar magnets and relate the strength of the field to the concentration of lines

  .The magnetic field is strongest at the poles

  -this is where the magnetic field lines are closest together

  .The magnetic field becomes weaker as the distance from the magnet increases

  -this is because the magnetic field lines are getting further apart
• 12.5 Describe the use of plotting compasses to show the shape and

  direction of the field of a magnet and the Earth's magnetic field

  1)Place the plotting compass near the magnet on a piece of paper.

  2)Mark the direction the compass needle points.

  3)Move the plotting compass to many different positions in the magnetic field, marking the needle direction each time.

  4)Join the points to show the field lines.

  (The needle of a plotting compass points to the south pole of the magnet)
• 12.6 Explain how the behaviour of a magnetic compass is related to

  evidence that the core of the Earth must be magnetic

  The needle of a plotting compass points to the south pole of the magnet. The behaviour of a compass shows that the Earth has a magnetic field. The Earth's core, which is made from iron and nickel, produces this magnetic field
• 12.7 Describe how to show that a current can create a magnetic

  effect and relate the shape and direction of the magnetic field

  around a long straight conductor to the direction of the current

  When a current flows through a conducting wire a magnetic field is produced around the wire

  A conducting wire is any wire that has current flowing through it

  The magnetic field is made up of concentric circles

  A circular field pattern indicates that the magnetic field around a current-carrying wire has no poles

  As the distance from the wire increases the circles get further apart

  This shows that the magnetic field is strongest closest to the wire and gets weaker as the distance from the wire increases

  The right-hand thumb rule can be used to work out the direction of the magnetic field
• 12.8 Recall that the strength of the field depends on...

  the size of the current and the distance from the long straight conductor
• 12.9 Explain how inside a solenoid (an example of an electromagnet)

  the fields from individual coils

  a) add together to form...

  a very strong almost uniform field along the centre of the solenoid
• 12.9 Explain how inside a solenoid (an example of an electromagnet)

  the fields from individual coils

  b) cancel to give...

  a weaker field outside the solenoid
• 12.10 Recall that a current carrying conductor placed near a

  magnet experiences...

  a force and that an equal and opposite force acts on the magnet
• 12.11 Explain that magnetic forces are due to...

  interactions between magnetic fields
• 12.12 Recall and use Fleming's left-hand rule to represent the

  relative directions of the force, the current and the

  magnetic field for cases where they are mutually

  perpendicular

  Hold your thumb, forefinger and second finger at right angles to each other:

  -the forefinger is lined up with magnetic field lines pointing from north to south

  -the second finger is lined up with the current pointing from positive to negative

  -the thumb shows the direction of the motor effect force on the conductor carrying the current