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Physics > Topic 7 - Magnetism and Electromagnetism > Flashcards

Topic 7 - Magnetism and Electromagnetism Flashcards

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1
Q

Like poles ….., unlike poles ……

A

Like poles repel
Unlike poles attract

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2
Q

What is the difference between a contact and a non-contact force?

A

Contact forces need to touch to act, non-contact don’t

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3
Q

Is magnetism a contact or non-contact force?

A

non-contact

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4
Q

What is a permanent magnet?

A

A permanent magnet produces its own magnetic field

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5
Q

What is an induced magnet?

A

An induced magnet becomes a magnet in a magnetic field

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6
Q

What are the 4 magnetic metals?

A
  • nickel
  • cobalt
  • iron
  • steel
    (NCIS)
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7
Q

Where is the field of a bar magnet strongest?

A

at the poles

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8
Q

What happens to the strength of a magnetic field the further away you go from a magnet?

A

the strength reduces the further away you go

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9
Q

What is a magnetic compass made of?

A

a magnetic compass is made of a small bar magnet

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10
Q

What direction does a magnetic compass point?

A

geographic North but magnetic South

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11
Q

What direction do magnetic field lines go in?

A

from North to South

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12
Q

How can we use a compass to plot the pattern of the magnetic field lines around a magnet?

A
  • place the compass near the magnet on a piece of paper
  • mark the direction the compass needle points
  • move the compass to many different positions in the magnetic field, marking the needle direction each time
  • join the points to show the field lines
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13
Q

What causes a wire to produce a magnetic field?

A

a current flowing through it

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14
Q

What do we call a long coil of wire?

A

a solenoid

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15
Q

Describe the magnetic field inside a solenoid

A

strong and uniform

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16
Q

What kind of magnet has the same magnetic field as a solenoid?

A

a bar magnet

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17
Q

What is the main advantage of using an electromagnet rather than a permanent magnet?

A

electromagnets can be switched off

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18
Q

Name 3 ways to make an electromagnet stronger

A
  • increase the current
  • increase the number of turns on the coil
  • add an iron core
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19
Q

Which rule do we use to draw the direction of the magnetic field around a straight wire?

A

the right hand rule

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20
Q

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

A
  • thumb = force
  • first finger = magnetic field
  • second finger = current
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21
Q

What is the equation linked to the left hand rule?

A

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

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22
Q

How does an electric motor work?

A
  • a coil of wire carrying a current in a magnetic field experiences a force that makes it rotate
  • a split ring commutator changes the direction every half turn
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23
Q

What is a magnet?

A

any material/object that produces a magnetic field

24
Q

What is a magnetic field?

A

the area around a magnet where it can act on another magnet or magnetic field

25
Q

How do you plot a magnetic field using iron filings?

A
  • place a piece of paper on top of the magnet
  • gently sprinkle iron filings on top of the paper
  • carefully tap the paper and iron will settle on the field lines
  • doesn’t show the direction of field lines (show doesn’t show which pole is which)
26
Q

The force between a permanent and induced magnet is always …

A

attractive

27
Q

What is an electromagnet?

A

a solenoid with an iron core

28
Q

How do you change the direction of a magnetic field in an electromagnet?

A

change the direction of the current

29
Q

Describe the right hand rule

A
  • can determine the direction of the magnetic field around a wire
  • thumb = direction of current
  • fingers = direction of field lines
30
Q

The motor effect occurs when:

A

a wire with a current flowing through it is placed in a magnetic field and experiences a force

31
Q

Why does the motor effect occur?

A
  • two magnetic fields are interacting (one around the wire, one between 2 magnets)
  • this means the wire will experience a force
32
Q

Name some factors that increase the size of the force (motor effect)

A
  • increase current in wire
  • use stronger magnets
  • place wire at 90° to the direction of the magnetic field lines
33
Q

What is the assumption we make when we use F = BIL?

A

that the wire is at 90° to the magnetic field lines

34
Q

Describe how electric motors work

A
  • current flows through the coil
  • this creates a magnetic field around the coil
  • the 2 magnetic fields interact
  • so a force is exerted on the coil
  • and the coil rotates
35
Q

What does a split ring communtator do?

A
  • swaps positive and negative connections every half turn
  • so the direction of the current swaps every half turn
  • so the forces acting on the coil will always act in the same direction
36
Q

How do you increase the speed of the rotations in an electric motor?

A
  • increase the current
  • use a stronger magnet
  • add more turns to the coil
37
Q

Simply define the generator effect

A

motion is being used to create electricity

38
Q

Simply define the motor effect

A

electricity is being used to create motion

39
Q

Describe the generator effect

A
  • coil cuts through the field lines
  • a potential difference is induced
  • there is a complete circuit so current flows
40
Q

Name some factors affecting the size of the p.d in a generator

A
  • speed at which the coil moves
  • number of turns in coil
  • strength of magnetic field
41
Q

Name the 2 types of generator

A

alternators and dynamos

42
Q

Describe the differences between alternators and dynamos

A

dynamos:
- have split ring commutators
- produce direct current
alternators:
- have slip rings and brushes
- produce alternating current

43
Q

Describe how alternators work

A
  • a coil of wire rotates
  • the coil cuts through the field lines
  • a potential difference is induced
  • there is a complete circuit so current flows
  • every half turn the p.d changes direction so the current changes direction
  • the slip rings and brushes mean the contacts don’t swap every half turn
44
Q

What are the purposes of slip rings in alternators?

A
  • they provide a continuous connect between the coil and the meter
  • they make sure the wires don’t get tangled
45
Q

Describe the current graph for an alternator

A

a classic wave that goes positive and negative (sine graph like)

46
Q

Describe how dynamos work

A
  • coil of wire rotates
  • the coil cuts through the field lines
  • a potential difference is induced
  • there is a complete circuit so current flows
  • every half turn, the two ends swap from one brush to the other
  • so the current doesn’t change direction
47
Q

What is the purpose of a split ring commutator in a dynamo?

A

it swaps the contacts each half turn, which means the current stays in the same direction

48
Q

Describe the current graph for dynamos

A

always positive - not a wave, looks more like mountains

49
Q

What is the similarity of loudspeakers and microphones?

A

they both convert between sound waves and electrical signals

50
Q

What effect do loudspeakers use?

A

the motor effect

51
Q

What is a loudspeaker’s role?

A

loudspeakers take electrical signals and convert them into vibrations, which generate sound waves

52
Q

How do loudspeakers work?

A
  • a.c flows through the wire and creates a changing magnetic field in the coil
  • the magnetic field of the coil interacts with the magnetic field of the permanent magnet
  • the interacting magnetic fields exert a force on the coil
  • this force will constantly change direction, making the coil oscillate and causes vibrations, creating sound waves
53
Q

What effect do microphones use?

A

the generator effect

54
Q

What is a microphone’s role?

A

microphones detect vibrations and convert these into electrical signals

55
Q

How do microphones work?

A
  • sound waves hit the diaphragm, causing the diaphragm to move
  • this causes the coil to move back and forth through the magnetic field of the magnet
  • the coil cuts through the field lines, inducing a p.d in the coil
  • the p.d is alternating, because coil is constantly changing direction
56
Q

A basic transformer consists of:

A
  • a primary coil
  • a secondary coil
  • an iron core
57
Q

How does a transformer work?

A
  • an alternating p.d is in primary coil - this causes a current (constantly changing direction) - this causes a changing magnetic field
  • this induces an alternating magnetic field in the iron core
  • this induces a changing magnetic field in secondary coil - cuts through secondary coil and induces a p.d
  • if part of a complete circuit, an alternating current will flow

Physics (8 decks)

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