Magnetism

Question 1

What is a permanent magnet?

Answer 1

A magnet that produces its own magnetic field

Question 2

What is an induced magnet?

Answer 2

A material that becomes magnetic when it comes into contact with a permanent magnetic field. It is always attracted to the permanent magnet. It loses its magnetism when it is moved away.

Question 3

What are the magnetic materials?

Answer 3

Iron, nickel, copper and the alloy of steel

Question 4

What is a magnetic field?

Answer 4

A region where other magnets or magnetic materials experience a force

Question 5

In what direction do the magnetic field lines point?

Answer 5

N to S

Question 6

What is a solenoid?

Answer 6

A wire that has been twisted into a coil that increases magnetic field strength

Question 7

What is a compass needle?

Answer 7

A compass needle is a small bar magnet that points towards the N pole of the earth if not interrupted by another magnetic field

Question 8

What is the right hand rule used for?

Answer 8

To determine the direction of force within a current carrying wire.

Question 9

What affects the magnetic field in a current carrying wire?

Answer 9

• distance from wire
• size of current

Question 10

What are the magnetic field lines like on a solenoid?

Answer 10

Same as a bar magnet

Question 11

What is the current like inside a solenoid and why?

Answer 11

Strong and uniform.
The turns in the coil create a stronger magnetic field

Question 12

What is an electromagnet?

Answer 12

A solenoid with an iron core that can be turned on and off

Question 13

What does the iron core in the electromagnet do?

Answer 13

Increases strength of the magnetic field

Question 14

What are electromagnets used in?

Answer 14

Fire alarm bells
scrap yards

Question 15

What is the motor effect?

Answer 15

When a magnet and current carrying conductor exert a force on each other.

Question 16

What is Flemmings left hand rule used for?

Answer 16

To determine the direction of force, magnetic flux density and current.

Question 17

What is the equation linked to Flemmings left hand rule?

Answer 17

F=BIL
Force = magnetic flux density x current x length of wire

Question 18

How can force be increased?

Answer 18

• By increasing magnetic flux density
• by increasing current
• by increasing length of conductor

Question 19

What is direct current?

Answer 19

Current that always flows in one direction. Its supplied by batteries.

Question 20

Why is a split ring commutator used?

Answer 20

Needed to ensure current is reversed every half turn to keep the coil spinning

Question 20

How does an electric motor work?

Answer 20

Direct current is passed through the coil.
Each side of the coil experiences opposing forces causing the coil to rotate.

Question 21

How do you increase the speed of the coil rotation?

Answer 21

• add more turns
• add more current/p.d.

Question 22

What is alternating current?

Answer 22

Current that flows in both directions. Supplied by mains.

Question 23

How do loudspeakers and headphones work?

Answer 23

Alternating current is sent through the coil. (= alternating force so alternating movement)
Coil moves back and forth and therefore the paper cone moves back and forth.
Sound waves are created.

Question 24

What is the generator effect?

Answer 24

When a p.d. is induced in a wire which is experiencing a change in a magnetic field. In a complete circuit a current is induced.

Question 25

Where is magnetic field strength the strongest?

Answer 25

At the poles

Question 26

Attraction and repulsion of magnets are examples of what type of force?

Answer 26

Non-contact forces.

Question 27

What does the direction of magnetic field lines show?

Answer 27

The direction of force that would act on the N pole if placed at that point

Question 28

What needs to be done to induce a p.d?

Answer 28

- move magnet - move wire

Question 29

What can be done to switch the direction of the p.d.

Answer 29

- move magnet in opposite directions - flip poles around - move wire in opposite directions - flip both poles on the magnets

Question 30

What can increase the size of the induced p.d.?

Answer 30

- increase the speed of movement - increase magnetic flux density

Question 31

How does a microphone work?

Answer 31

Sound waves hit the diaphragm causing it to move back and forth. The coil then moves back and forth producing an alternating current.

Question 32

What is the difference between an alternator and a dynamo?

Answer 32

An alternator indices an alternating current. There is slip rings but no split ring commutator so the current is not being reversed every half turn. Dynamos induce a direct current. There is a split ring commutator to reverse the current every half turn.

Question 33

What is the difference between a step up transformer and a step down transformer?

Answer 33

A step up transformer has fewer turns on the primary coil as opposed to the turns on the secondary coil. A step down transformer has more turns on the primary coil as opposed to the turns on the secondary coil.

Question 34

Why is an iron core used in the transformer?

Answer 34

It’s easily magnetised

Question 35

What do step up transformers do and why?

Answer 35

Step up transformers increase the voltage by increasing the number of turns on the secondary coil. An alternating current is passed through the primary coil and creates a magnetic field. This induces a current in the secondary coil. The iron core carries no current or electricity. This decreases the current as V and I are inversely proportional. This reduces the resistance and therefore heat loss. P = VI

Question 36

What do step down transformers do and why?

Answer 36

They decrease the voltage in the wire as the number of turns on the secondary coil decreases. The current in the primary coil induces a magnetic field which in turn induces the current in the secondary coil. Voltage is decreased as current increases allowing 230V to be supplied to the mains. Much safer.