Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Physics > Magnets & Electromagnets > Flashcards

Magnets & Electromagnets Flashcards

1
Q

Define a magnetic field?

A

A magnetic field is a region where a magnetic pole experiences a force acting on it

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What does the direction of a magnetic field line at a point show?

A

The direction of the force that would act on a North Pole of a magnet placed at that point

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How is the force of attraction experienced?

A

Between two unlike poles caused by the two fields connecting

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How is the force of repulsion experienced?

A

By two like poles, due to two opposing fields diverging because they are unable to overlap

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Where is the magnetic field of a magnet strongest & how is this shown?

A

Near its poles & lines are closest together

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What causes magnetic forces?

A

Interactions between magnetic fields

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Give examples of & describe a magnetic material?

A

Iron, cobalt, steel & nickel.
Experience a force in a magnetic field.
The force between a magnet and magnetic material is always attractive

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What happens if a magnetic material is placed into a magnetic field?

A

The magnetic material is magnetised & becomes an induced magnet because permanent magnets have a magnetic field all the time.
This is called induced magnetism.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is induced magnetism?

A

Placing a magnetic material into the magnetic field of a permanent magnet, like a bar magnet.
The magnetic material then gets its own poles and magnetic field.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the properties of temporary magnets?

A

Made out of soft iron
Gain & lose magnetism quickly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the properties of permanent magnets?

A

Made out of steel
Take longer to become magnetised & keep their induced magnetism for longer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the difference between magnetic and non-magnetic materials?

A

Magnetic materials experience a force in a magnetic field.
Non-magnetic materials don’t.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are examples of non-magnetic materials?

A

Plastic
Rubber
Glass
Wood

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Which direction does a compass needle point in?

A

The direction of the magnetic field it is in.
The North Pole of the bar magnet inside the needle is attracted to the South Pole of any nearby magnet.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How can you plot the direction of a magnetic field with a compass?

A

Place the magnet on a piece of card and draw around it.
Place the compass on the card near the magnet.
The needle will point in the direction of of the field line & draw two dots at each end.
Move the compass so the tail end of the needle is where the tip end of the needle was before & join them up.
Repeat for several field lines.
Draw arrows from north - south.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Why can iron filings show the direction of magnetic field lines?

A

Iron is a magnetic material so iron filings become very small magnets in a magnetic field, like compass needles.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How can iron filings show the direction of magnetic fields?

A

Place a magnet under a piece of card.
Scatter iron filings over the card.
Tap the card until iron filings form a clear pattern.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Define an electromagnet?

A

A solenoid with a soft iron core

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How are electromagnets made?

A

A block of soft iron is placed into a coil which increases the solenoid’s magnetic field strength.
This is because the soft iron is easily magnetised by the solenoid & becomes an induced magnet when current flows, which adds to the magnetic effect.
Switching off the current makes the magnetic field disappear because the soft iron is easily demagnetised.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What are advantages of using electromagnets?

A

They can be turned on & off easily.
They can be made stronger than permanent magnets.
Their strength can be varied by changing the current.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What are the uses of electromagnets?

A

In relays - electric switches used in circuits.
Allows the small current of an electromagnet to turn on a larger current in a second circuit.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What are 2 uses of permanent magnets?

A

Fridge magnets.
Encoding information in the magnetic strip of a credit card.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Describe the pattern & direction of the magnetic field due to current in a straight wire?

A

RHG rule
Point thumb in the direction of current.
Direction of fingers is the direction of the magnetic field.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Describe the pattern & direction of the magnetic field due to current in a solenoid?

A

Same as a bar magnet

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is a solenoid?

A

A current-carrying wire wrapped into a coil

26
Q

How does the magnetic field inside & outside the solenoid work?

A

Inside - magnetic field lines around each loop of wire line up with each other - lots of straight field lines pointing in same direction.
Outside - same as a bar magnet.

27
Q

What is the experiment to identify pattern of magnetic field around a straight wire?

A

Thread a straight wire through the hole in a piece of card.
Use a compass or iron filings to find the direction of the magnetic field lines.

28
Q

What is the experiment to identify pattern of magnetic field around a solenoid?

A

Push a solenoid halfway through slits in the piece of card.
Use a compass or iron filings to find magnetic field lines

29
Q

What happens if you increase the magnitude of the current in a straight wire or solenoid?

A

The magnetic field gets stronger.

30
Q

What happens if you change the direction of the current in a straight wire or solenoid?

A

The direction of the magnetic field changes

31
Q

Why is the magnetic field inside a solenoid strong & uniform?

A

Because the field lines of each loop of the solenoid line up.

32
Q

Outside the solenoid, where is the magnetic field strongest?

A

Near the poles - field lines drawn closest together

33
Q

What are applications of relays?

A

Cars - control headlights & windscreen wipers

34
Q

Describe an experiment to show that a force acts on a current-carrying conductor in a magnetic field.

A

Place a set of rails inside a horseshoe magnet with a bar on top of the rails - complete circuit is formed.
When a current flows through the rails, a force rolls the bar along the rails.
Strength of the force increases with the strength of the magnetic field & amount of current passing through the conductor.

35
Q

What happens if the current or direction of the field is reversed?

A

The bar will roll in the opposite direction

36
Q

What is a current?

A

A flow of charged particles

37
Q

How can we determine direction of a force on beams of charged particles?

A

Use LHR
Negative particles’ current is in the opposite direction to their movement.
Force is in the direction of movement.

38
Q

What happens if you twist a current-carrying wire into a coil & put it into a magnetic field?

A

The forces on the current-carrying coil make it experience a turning effect.

39
Q

How can you increase the turning effect on a coil?

A

Increase the number of turns on the coil
Increase the current of the coil
Increase the strength of the magnetic field

40
Q

Describe the operation of a DC motor?

A

A current carrying conductor in a magnetic field experiences a force.
When a direct current is turned on in the coil, forces act on the two side arms of the coil.
One force acts upwards, and one force acts downwards, so the coil rotates on its axis.
The split-ring commutator rotates with the coil, & because the coil is turning, it swaps which sides of the commutator are touching which brushes every half turn, swapping the direction of the current through the coil every half turn.

41
Q

What is the purpose of the split-ring commutator?

A

It reverses the current in the coil every 180 degrees.
It ensures the coil keeps spinning continuously, otherwise the direction of the force on the coil would be reversed every half turn.

42
Q

What is the purpose of the brushes?

A

They allow the coil to rotate freely without tangling the circuit.

43
Q

How is charge measured?

A

In coulombs

44
Q

Define an electric field?

A

A region in which an electric charge experiences a force

45
Q

What is the direction of an electric field at a point?

A

The direction of the force on a positive charge at that point

46
Q

Describe the electric field around two oppositely charged parallel plates?

A

Uniform

47
Q

How does the charging of solids by friction work?

A

When insulating materials rub together, electrons are scraped off one & dumped on the other, due to friction.
The one that gains electrons gets a negative charge & the solid that loses electrons gets a positive charge.

48
Q

Define an electrical conductor?

A

Conduct charge easily.
Current (electrons) can easily flow through them.
Metals e.g. copper & silver

49
Q

Define an electrical insulator?

A

Don’t conduct charge easily.
Current can’t flow.
E.g. plastic & rubber.

50
Q

How can we distinguish between electric conductors & insulators?

A

Attach a crocodile clip to each end of a material & add to a circuit.

For the bulb to light, a current must be flowing in a complete circuit, and if it’s a conductor, the current can flow through so the bulb will light.

If it’s an insulator, the bulb won’t light as current can’t pass through, so the circuit is incomplete.

51
Q

Why can current flow in metals/electrical conductors?

A

Atoms contain a nucleus of positive protons & neutral neutrons, orbited by negatively charged electrons.

Metals are made up of a lattice of positive ions surrounded by free electrons.
These electrons are free to move throughout the metal & electric current in metals is the flow of these electrons.

52
Q

Why can’t current flow in insulators?

A

Atoms hold on to their electrons tightly.
These electrons can’t move so a current can’t flow.

53
Q

How can we show the production of electrostatic charges by friction?

A

Rub hair with balloon.
Electrons transferred from hair to balloon.
Balloon becomes negatively charged & hair positive.
Both oppositely charged so they attract each other.

54
Q

How can we show the detection of electrostatic charges?

A

Suspend a rod with a known charge from a string (free to move)
Object with same charge will repel it & oppositely charged will attract.

55
Q

What is the definition & three ways of magnetisation?

A

Lining up magnetic domains to make a magnet.

Stroke with a permanent magnet.
Place inside strong DC coil.
Heat then cool in a strong magnetic field.

56
Q

What are three ways of demagnetisation?

A

Whack with a hammer
Heat & cool aligned East-West
Slowly remove from AC coil

57
Q

How can we make an electromagnet stronger?

A

Add a soft iron core
Increase the current in the solenoid
More turns in the solenoid

58
Q

How does a loudspeaker work?

A

Alternating current in the coil at 90 degrees to the field lines forces the cone up & down.
This creates a sound wave.
The frequency of the alternating current is the frequency of the sound wave.

59
Q

How does a smoke precipitator work?

A

Smoke passes up a chimney through +ve mesh & gains a positive charge.
It is then attracted to negative plates.
So the smoke doesn’t escape into the atmosphere

60
Q

How do lightning conductors work?

A

Fitted to tall buildings.
It provides a conducting route for current to flow through so the building isn’t damaged.

Physics (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions