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Physics 🔭 > P4 Magnetism > Flashcards

P4 Magnetism Flashcards

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1
Q

Magnetism describes…

A

The ability of magnets to attract + repel other magnets without touching them

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2
Q

What are the two poles of a magnet?

A

North and south

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3
Q

A magnetic field is…

A

The area around a magnet where another magnet or magnetic material feels a force

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4
Q

What are four examples of magnetic materials

A

Iron
Nickel
Cobalt
Steel

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5
Q

The magnetic field is strongest where?

A

At the magnet’s poles

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6
Q

How can you make an iron nail magnetic?

A

By running a magnet repeatedly over the nail in the same direction

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7
Q

By making a nail magnetic it becomes an ____ magnet
Over time it will _____

A

Induced
Demagnetise

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8
Q

Magnetic field lines always point…

A

From north to south

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9
Q

The strength of a field is shown by?

A

How close together the field lines are

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10
Q

Bar magnets are _____ magnets and contain _____ magnetic domains

A

Permanent
Aligned

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11
Q

What is different about the Earth’s magnetic field?

A

The magnetic South Pole is in the northern hemisphere

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12
Q

What is the right hand grip rule

A

Thumb points along direction of current
Other fingers give direction of field

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13
Q

The magnetic field pattern around a _____ (coil) takes the same shape as that around a bar magnet
Strength of field increased by?

A

Solenoid
1. Adding more turns to coil
2. Increasing current
3. Adding iron core

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14
Q

What are 3 advantages of using electromagnets instead of permanent magnets?

A
  1. Can be switched on and off
  2. Can change its strength (increase/decrease current)
  3. Can swap their polarity
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15
Q

What is the motor effect

A

Putting a current-carrying wire in a magnetic field will produce a force

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16
Q

Why does the motor effect occur

A

Current in wire produces a magnetic field
This interacts with field of magnet
Produces a force
Only happens if wire cuts field lines

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17
Q

How do we predict direction of force for a motor?

A

Fleming’s left hand rule

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18
Q

What does each finger represent in Fleming’s left hand rule?

A

Thumb = motion
First finger = field
Second finger = current

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19
Q

What kind of current is shown by the second finger?

A

Conventional current (positive to negative)

20
Q

How do we increase strength of force exerted in a motor?

A

F=BIL - increasing any of these will increase force
1. More current
2. Stronger magnet
3. More turns to coil

21
Q

What is the role of a split ring commutator

A

To keep the coil rotating in the same direction

22
Q

Explain how a loudspeaker works

A
  1. Current flowing through coil causes a force due to the motor effect
  2. Direction of force given by Fleming’s left hand rule
  3. As current alternates, diaphragm moves in and out
  4. Causes sound waves in air
23
Q

What is the difference between motors and electromagnetic induction (generators)?

A

Motors have a current in a wire which produces a force
Generators have a moving wire which produces a current

24
Q

When a coil of wire is rotated in a magnetic field…

A

An electric current will be generated

25
Q

Direction of induced current in a generator is worked out using which hand rule?

A

Fleming’s right hand rule

26
Q

What do the fingers represent in Fleming’s right hand rule?

A

Thumb = direction conducting wire moves (motion)
First finger = field
Second finger = current

27
Q

What is a DC signal

A

One in which the electrons flow in one direction around the circuit

28
Q

Explain how a DC generator works

A

Moving wire through field induces current
Split ring commutator means direct current is produced
Direction of current found using Fleming’s right hand rule

29
Q

What is an AC signal

A

One in which the current switches directions, so the electrons move backwards and forwards about a point

30
Q

Explain how an AC generator works

A

Moving wire through magnetic field induces current
Slip ring commutator produces alternating current
Direction of current found using Fleming’s right hand rule

31
Q

Explain how a motor works

A

Coil of wire between poles of magnet
Current in the wire produces magnetic field which interacts with field of permanent magnet, creating a force
Direction of force found using Fleming’s left hand rule
Split ring commutator switches direction of current to allow motor to keep rotating

32
Q

Permanent magnets always produce

A

Their own magnetic field

33
Q

Temporary / induced magnets produce

A

A magnetic field only when they’re in the presence of another magnet

34
Q

What are magnetically soft materials

A

Magnetic materials that gain and lose magnetism quickly

35
Q

What are magnetically hard materials

A

Magnetic materials that gain and lose magnetism slowly

36
Q

To experience the full force, a current carrying wire must be…

A

Perpendicular to magnetic field

37
Q

An example of a magnetically soft material

A

Iron

38
Q

An example of a magnetically hard material

A

Steel

39
Q

The force between a permanent and induced magnet will…

A

Always be attractive

40
Q

Magnetic field lines can show…

A

Strength of magnet at particular point
Whether 2 magnets would attract or repel
Direction a compass would point at that point

41
Q

When an electrical current flows through a material…

A

A magnetic field is always produced

42
Q

What is the function of a loudspeaker

A

To convert electrical signals into sound waves

43
Q

Name three ways to increase size of potential difference generated in electromagnetic induction

A

Increase magnetic field strength
Move coil through field faster
Add more turns to coil

44
Q

Difference between design of alternator and design of dynamo?

A

Alternator = slip rings
Dynamo = split ring

45
Q

A wire moving up and down perpendicular to a magnetic field will…

A

Generate an alternating potential difference

46
Q

When a wire experiences a ___ magnetic field, a potential difference will be ___
If the ends of wire are connected to make a ___ circuit, a ___ will flow

A

Changing
Induced
Closed
Current

47
Q

A wire moving parallel to a magnetic field will

A

Not generate a potential difference

Physics 🔭 (12 decks)

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