P4

Question 1

Like poles …

Answer 1

repel

Question 2

Unlike poles …

Answer 2

attract

Question 3

What are magnetic field lines?

Answer 3

A way of modelling a magnetic field

Question 4

What do field lines represent?

Answer 4

Magnetic flux

Question 5

Magnetic flux density (magnetic field strength)

Answer 5

the number of field lines passing through a particular area

Question 6

What direction do magnets move in?

Answer 6

The direction that makes the field lines shorten

Question 7

Draw a diagram of magnetic field patterns around bar magnets to show attraction and repulsion

Answer 7

see p.g. 120

Question 8

What is a permanent magnet?

Answer 8

A permanent magnet is made up of many small domains (magnetic regions) that all line up

Question 9

What is an induced magnet?

Answer 9

an induced magnet is made up of domains that don’t generally line up but when placed in a magnetic field they do line up

Question 10

What is a compass?

Answer 10

A compass is a ‘north seeking’ pole

Question 11

How is the behaviour of a compass related to the evidence that the core of the Earth must be magnetic?

Answer 11

As the Earth behaves as though it has a large bar magnet at its centre, and the compass needle lines up with the magnetic field of the Earth.

Question 12

How can you show that a current can create a magnetic effect?

Answer 12

By using a compass

Question 13

Describe how to show the directions of the magnetic field around a conducting wire

Answer 13

You can use your right hand to work out the direction of a magnetic field around a current. If the current is coming towards you the field lines are anticlockwise

Question 14

What does the strength of the field depend on?

Answer 14

The current and the distance from the current

Question 15

What is a solenoid?

Answer 15

Many parallel loops that make a coil

Question 16

Explain how solenoid arrangements can enhance the magnetic effect

Answer 16

Adding together many fields produces a much stronger field than that of a single wire
A core magnetic field also makes the field stronger

Question 17

How do a magnet and current-carrying conductor exert a force on one another?

Answer 17

If the current-carrying wire is placed in a magnetic field (whose lines of force are at right angles to the wire) then it will experience a force at right angles to both the current direction and the magnetic field lines.

Question 18

What is Flemings left hand rule and how do we use it?

Answer 18

Flemings left hand rule is used to represent the force (thumb), magnet field (first finger) and current (second finger)
Useful memory tip - FBI

Question 19

What is the equation to calculate the force on a conductor?

Answer 19

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)

Question 20

How is the force exerted from a magnetic and current-carrying conductor used to cause rotation in electric motors?

Answer 20

When you connect a wire to a battery in a magnetic field, one side of the wire goes upwards and another side of the wire goes downwards.

Question 21

Why are split ring commutators used in motors?

Answer 21

A split ring commutator enables the current to flow the same way from the battery, but change to different halves of the coil as it spins. This ensures the force on one side of the coil is upwards and another is downwards, ensuring the motor spins the same way

Question 22

How can you change the speed of a motor? (4)

Answer 22

By changing:
the magnitude of the current flowing in the coil
the strength of the magnetic field
the number of coils in the wire
the length of the coil