P14,P15

Question 1

What are the 2 poles of a magnet?

Answer 1

North and South

Question 2

Where is the magnetic force the strongest?

Answer 2

Near the magnet’s poles

Question 3

What sort of force is magnetic force?

Answer 3

A non-contact force

Question 4

Name 3 magnetic materials

Answer 4

Iron, Cobalt, Nickel

Question 5

What is a permanent magnet?

Answer 5

An object that gets magnetized and creates its own persistic magnetic field, always causing a force on other magnets

Question 6

What are induced magnets?

Answer 6

Induced magnets are magnetic materials that turn into a magnet when they are put into a magnetic field.

Question 7

What direction do magnetic field lines go?

Answer 7

North to South

Question 8

What produces Earth’s magnetic field?

Answer 8

The molten iron in the outer core of the Earth which due to the Earth’s rotation and axis, creates a magnetic field

Question 9

What is the force between a permanent and induced magnet?

Answer 9

The force between a permanent and induced magnet is always attractive, irrespective of the poles.

Question 10

What happens when an induced magnet moves far away from a permanent magnetic field?

Answer 10

Its magnetism weakens, until it moves to a point where its magnetism is completely lost

Question 11

When not near a magnet, why does a compass always point north?

Answer 11

Because that’s where Earth’s south magnetic pole is located, meaning they attract

Question 13

What happens when a current flows in a wire?

Answer 13

It creates a circular magnetic field around the wire

Question 14

What is an electromagnet?

Answer 14

A magnet made by wrapping a coil of wire around an iron bar and passing an electric current through the coil

Question 15

What are electromagnets most commonly used for?

Answer 15

• Electric motors
• Headphones

Question 16

What is a solenoid?

Answer 16

A coil of wire which when current passes through creates a strong magnetic field

Question 17

Describe the magnetic field found inside a solenoid

Answer 17

Strong and uniform

Question 18

What is the motor effect?

Answer 18

A wire carrying a current creates a magnetic field. This can interact with another magnetic field, causing a force that pushes the wire at right angles.

Question 19

How can the size of the force be increased in the motor effect?

Answer 19

• increasing the current
• using a stronger magnet

Question 20

When is the force in the motor effect greatest?

Answer 20

When the wire is perpendicular to the magnetic field

Question 21

When is the force zero in the motor effect?

Answer 21

When the wire is parallel to the magnetic field lines

Question 22

What is the magnetic flux denisty?

Answer 22

The measure of the strength of the magnetic field

Question 23

What is the unit for magnetic flux density?

Answer 23

Tesla (T)

Question 24

How can the direction of a motor be reversed?

Answer 24

• Reversing the current
• Reversing the field by swapping the magnetic poles

Question 25

Why does a motor spin when a current is passed through the coil?

Answer 25

- A force acts on each side due to the motor effect - The force on one side is opposite to the force on the other side

Question 26

What does the split-ring commutator do in a motor?

Answer 26

Reverses the current around the coil every half-turn (90 degrees). The momentum of the motor, carries it past 90 degrees. The sides then swap over meaning the coil is pushed in the same direction every half-turn.

Question 27

What is electromagnetic induction?

Answer 27

When motion between a conductor and a magnetic field creates electricity, ie a magnet is moved into a coil of wire.

Question 28

What is electromagnetic induction often referred to as?

Answer 28

The generator effect

Question 29

When does an induced voltage produce an induced current (generator effect)?

Answer 29

If the conductor is connected in a complete circuit.

Question 30

How can you increase the induced current/p.d? (generator effect)

Answer 30

- speed of movement increased - magnetic field increased - number of turns coil is increased

Question 31

What factors affect the direction of the induced potential/current (generator effect)?

Answer 31

- magnet moved out of coil - other pole of magnet is moved into the coil

Question 32

Why does the induced current always oppose the original change that made it?

Answer 32

The magnetic field created by an induced current always acts against the change that made it. For example, if the north pole of a magnet enters a coil, the coil will repel it to return things to the way they were. If the magnet moves away, the coil will attract it.

Question 33

Why can transformers only work with alternating current?

Answer 33

A changing magnetic field is required to induce an alternating current in the secondary coil

Question 34

What are transformers used for?

Answer 34

Increasing/decreasing the size of an alternating potential difference

Question 35

How does a transformer work (5 marks)?

Answer 35

1. primary voltage carries ac through primary coil 2. primary coil produces magnetic field which changes current 3. iron core increases 4. changing magnetic field induces potential difference in secondary coil 5. induced pd produces ac in external current

Question 36

Difference between step-up and step-down transformers

Answer 36

- Step-up transformers have more turns on the secondary coil than the primary coil (increases p.d) - Step-down transformers have less turns on the secondary coil than the primary coil (reduces p.d)

Question 37

How does a transformer produce an induced current?

Answer 37

An alternating voltage is applied to one coil (the primary coil). This causes a changing (alternating) magnetic field to be set up in the core. The other coil (the secondary coil) is in this changing magnetic field and so it has an alternating voltage induced in it.

Question 38

Why is iron used as the core of a transformer?

Answer 38

It is easily magnetised

Question 39

What would happen if transformers were 100% efficient?

Answer 39

The electrical power output would equal the electrical power input

Question 40

What type of current do dynamos produce?

Answer 40

Direct

Question 41

2 types of generators

Answer 41

- Dynamos - Alternators

Question 42

How can the size of the induced voltage in a generator be increased>

Answer 42

- rotating coil or magnet faster - using a magnet with stronger magnetic field - having more turns of wire in coil - having iron core inside coil

Question 43

What does the thumb indicate in flemings left hand rule?

Answer 43

Force/Motion