P7

Question 1

Magnetic field

Answer 1

• region where other magnets/magnetic materials experience a non contact force.
• shown with magnetic field lines.
• lines go from north to south.
• closer lines=stronger magnetic field.

Question 2

Magnets

Answer 2

• 2 poles (north and south)
• force between magnet and magnetic material is always attractive, no matter the pole.
• 2 poles near each other exert force on each other:
  attractive or repulsive.
• like poles repel, unlike poles attract.

Question 3

Compasses

Answer 3

• inside is a tiny bar magnet.
• north pole of it is attracted to south pole of any magnet near, so compass points in direction of magnetic field it is in.
• points towards earths magnetic field.
• move compass around magnet, trace position on paper to build pic of what magnetic field looks like.

Question 4

Two types of Magnet

Answer 4

• Permanent: produce own magnetic field.
• Induced: magnetic materials turning to magnets when put in a magnetic field.
• Force between them is always attractive.
• Take away magnetic field, induced loses magnetism.

Question 5

Moving charge

Answer 5

• Flowing current through wire means magnetic field is created round wire.
• Field is made of concentric circles perpendicular to wire, wire in the centre.
• See this by placing compass near wire carrying a current, move compass, it traces direction of field.
• Change direction of current changes direction of field, use right hand thumb rule to work out which way.
• Strength of field changes with current and distance from wire.

Question 6

Right Hand Thumb Rule

Answer 6

• Using right hand, point thumb in direction of current and curl fingers.
• Direction of fingers = direction of field.

Question 7

Solenoid

Answer 7

• Wrapping wire into coil increases strength of field.
• Bc field lines round each wire loop line up together.
• Results in lots of field lines pointing in same direction that are v close together.
• Increase field strength more by putting iron core (induced magnet) in centre of coil.
• Solenoid with iron core is called ELECTROMAGNET.

Question 8

Magnetic field in solenoid

Answer 8

• Strong and uniform.
• Outside the field is like a bar magnet.
• This means that ends of solenoid act like north and south pole of bar magnet.
• Work out which side is north/south with right hand thumb rule.

Question 9

The Motor Effect

Answer 9

• When a current carrying wire is between magnetic poles, the field around the wire interacts with field it’s been placed in.
• Causes magnet and conductor to exert force on each other. Can cause wire to move.

Question 10

Force acting on a conductor depends on:

Answer 10

1. Magnetic flux density - how many field lines in a region. Shows strength of field.
2. Size of current through conductor.
3. Length of conductor in magnetic field.
   force = magnetic flux density x current x length

Question 11

Left Hand Rule

Answer 11

1. Using left hand, point First finger in direction of Field.
2. Point seCond finger in direction of Current.
3. ThuMb will then pont in direction of force (Motion).
   - Shows if either current or field is reversed, then direction of forces will be reversed.