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Physics > P2- Topic 7- Magnetism and Electromagnetism > Flashcards

P2- Topic 7- Magnetism and Electromagnetism Flashcards

1
Q

At which part of a magnet are the magnetic forces

strongest?

A

The poles of the magnet.

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2
Q

What happens when two magnets are brought close

to each other

A

They exert a force on each other

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3
Q

What type of force is exerted if two like poles of a

magnet are brought near each other?

A

A repulsive, non-contact force.

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4
Q

What type of force is exerted if two unlike
poles of a magnet are brought near each
other?

A

An attractive, non-contact force

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5
Q

What is the difference between a permanent magnet and an induced magnet? 2

A

● A permanent magnet produces its own
magnetic field
● An induced magnet becomes magnetic
when placed in a magnetic field

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6
Q

What type of force does induced

magnetism always cause?

A

A force of attraction

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7
Q

What happens when an induced magnet is removed

from a magnetic field?

A

The induced magnet loses most/all of its

magnetism.

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8
Q

What is a magnetic field?

A

The region around a magnet where a force acts on another magnet
or on a magnetic material (iron, steel, cobalt and nickel)

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9
Q

Give four examples of magnetic materials. 4

A
  1. Iron
  2. Steel
  3. Cobalt
  4. Nickel
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10
Q

What can always be said about the force between a

magnet and a magnetic material?

A

The force between a magnet and a magnetic material is always one
of attraction

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11
Q

How does the strength of a magnetic field alter as you move further away from
the magnet producing it?

A

The magnetic field strength decreases

the further you move away

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12
Q

In what direction does a magnetic field point? 2

A

● In the direction that a north pole would
experience a force if placed in the field
● From the north seeking pole to the
south seeking pole of a magnet

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13
Q

What does a magnetic compass contain?

A

A small bar magnet that points in the direction of the Earth’s magnetic field

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14
Q

describe how to plot the magnetic field pattern of a magnet using a compass 4

A
  1. place the plotting compass near the magnet on a piece of paper.
  2. mark the direction the compass needle points.
  3. move the plotting compass to many different positions in the magnetic field, marking the needle direction each time.
  4. join the points to show the field line
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15
Q

what do lines close together on a magnetic field line pattern

A

where the lines are close together it shows where the field is strongest
strongest part of the field are at the poles of the magnet

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16
Q

how is the core of the earth magnetic 2

A

When a plotting compass is placed in the Earth’s magnetic field, the north pole of the compass will line up with the Earth’s magnetic field lines and point to magnetic south

The core is magnetic, and creates a large magnetic field around
the Earth

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17
Q

What is produced when current flows through a

conducting wire?

A

A magnetic field is produced around the

wire

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18
Q

What determines the strength of the magnetic field around a current-carrying wire? 2

A

The magnitude of the current flowing through the wire

● The distance from the wire

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19
Q

What is a solenoid?

A

A coil of wire which when current passes

through creates a strong magnetic field

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20
Q

Describe the magnetic field found inside a solenoid

A

Strong and uniform

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21
Q

What is an electromagnet?

A

a solenoid with an

iron core.

22
Q

describe right hand grip rule 2

A

thumb point in the direction of the current

other fingers give the direction of the magnetic field

23
Q

what dictates the strength if a magnetic field 2

A

greater current = stronger magnetic field

greater distance from wire= weaker field

24
Q

why does adding the iron core increases the strength of the magnetic field

A

it is easier for magnetic field lines to pass through than air

25
Q

factors that affect the strength of the electromagnet

A 
size of the current
length
cross sectional area
number of turns (coils)
using a soft iron core
26
Q

What is the motor effect?

A

When a force is exerted between a
magnetic field and a current-carrying
conductor placed in that field

27
Q

What rule is used to determine the force

experienced due to the motor effect?

A

Fleming’s Left-Hand Rule

28
Q

describe Fleming’s Left-Hand Rule

A

thumb= direction of force

1st finger= direction of magnetic field

2nd finger= points in direction of current flow in the conductor

29
Q

What factors affect the size of

the force on a current-carrying wire in a magnetic field? 2

A

The magnitude of the current flowing
through the conductor
● The strength of the magnetic field that
the conductor is placed in

30
Q

If the direction of current in a current-carrying wire placed in a uniform
magnetic field is reversed, what happens to the force?

A

The direction of the force is reversed.

31
Q

If the strength of the current in a current-carrying wire placed in a uniform magnetic field is increased, what happens to the force?

A

The strength of the force is increased.

32
Q

What criteria must be met for the equation linking
force, magnetic flux density, current and length to
work ?

A

The conductor must be at right-angles to 90⁰

the magnetic field it is placed in

33
Q

What is the unit used for magnetic flux density?

A

Tesla, T

34
Q

electromagnetic devices

A

4.7.2.3 flash 2.29

35
Q

How does an electric motor work?3

A

● A coil of wire, carrying a current, is placed
in a magnetic field
● The forces on the two sides perpendicular
to the field experience forces in opposite
directions
● This causes a rotational effect

36
Q

how may another way electric motors work 6

A
  • permanent Magnets lie in fixed positions
  • In between, a coil of current-carrying wire lies on an axis

o Force on one side moves that side up

o Force on the other side (where current is flowing in opposite direction) moves down

o This can be verified using Fleming’s Left Hand Rule
- Hence it rotates

37
Q

How do loudspeakers make use of the motor effect? 2

A

The motor effect is used to convert variations in the current of an electrical
circuit
into the pressure variations which produce audible sound.

38
Q

Explain how a loudspeaker works 3

A

● A cone with a wire wrapped around it is connected to an a.c power supply and is placed in a permanent magnetic field
● When current flows through the wire, it creates a second magnetic field, which interacts with the
permanent field
● This produces a force which causes the cone to vibrate

39
Q

How is the pitch of the sound from a loudspeaker

changed? 2

A

● The frequency of the a.c current is altered

● This creates a different frequency of vibration in the cone

40
Q

What happens when an electrical conductor moves

relative to a magnetic field?

A

A potential difference is induced across the ends of the conductor.

41
Q

What happens to an electrical conductor

when there is a change to the magnetic field that it is placed in?

A

A potential difference is induced across the ends of the conductor

42
Q

What is the requirement for an induced potential difference to cause a current flow?

A

The conductor must form a closed loop or be part of a complete circuit.

43
Q

What can be said about the direction of the magnetic field produced by an induced current?

A

● The direction of the field is such that it opposes the change that induced the
current
● This change is either the movement of the conductor or a change to the field

44
Q

What are two ways that the generator
effect is used to generate different types
of current? 2

A

● In an alternator to produce
alternating-current
● In a dynamo to produce direct-current

a.c & d.c

45
Q

what is the generator effect

A

A potential difference or voltage is needed to make an electric current flow in a circuit.
electromagnetic induction = generator effect

46
Q

How does a microphone use the generator effect?

A

● It converts the pressure variations in
sound waves into alternating current in
a circuit

47
Q

Describe the makeup of a basic transformer

A

A primary coil and a secondary coil of

wire wrapped around an iron core.

48
Q

Why is iron used as the core for a transformer?

A

It is easily magnetised.

49
Q

Why must the current flowing through the

primary coil of a transformer be alternating? 3

A

For current to be induced in the secondary
coil, the magnetic field in the core must be
continuously changing
● For the magnetic field to be changing, the
current in the primary coil must be alternating

50
Q

What can be said about the electrical power input and output of a 100% efficient transformer? (

A

The electrical power input is equal to the

electrical power output.

Physics (10 decks)

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