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physics paper 2 🎀 > magnetism > Flashcards

magnetism Flashcards

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1
Q

which poles attract, and which repel?

A

LIKE
repel

UNLIKE
attract

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2
Q

what is a permanent magnet?

A

a magnet that produces its own magnetic field

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3
Q

what is an induced magnet?

A

a material that becomes a magnet when placed in a magnetic field

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4
Q

define magnetic field

A

the region around a magnet where a force acts on a magnet/ another magnetic material

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5
Q

the force between a magnet and a magnetic material is…

A

… always one of attraction

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6
Q

give evidence, regarding a compass, that the earth’s core is magnetic

A
  • a magnetic compass contains a small bar magnet
  • the earth has a magnetic field
  • the compass needle points in the direction of the magnetic field
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7
Q

what happens when a current flows through a conducting wire?

A

a magnetic field is produced around the wire

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8
Q

what determines the strength of a current-carrying wire?

A
  • the magnitude of the current flowing through the wire
  • distance from the wire
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9
Q

what is an electromagnet?

A

a solenoid with an iron core

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10
Q

explain what the motor effect is

A

when a conductor carrying a current is placed in a magnetic field, the magnet producing the field and the conductor exert a force on each other

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11
Q

state the direction each finger points in, during fleming’s left hand rule

A

THUMB- force
INDEX- magnetic field
MIDDLE- current

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12
Q

recall factors that effect the size of the force on the conductor

A

force on the conductor increases as…
- current increase
- magnetic field strengths
- a longer conductor is used

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13
Q

give four examples of magnetic materials

A
  • iron
  • nickel
  • cobalt
  • steel
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14
Q

define the term solenoid

A

a coil of wire which, when current passes through, creates a strong magnetic field

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15
Q

describe the magnetic field found inside a solenoid

A

strong and uniform

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16
Q

what is the unit used for magnetic flux density?

A

tesla, T

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17
Q

how does an electric motor work?

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
18
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

19
Q

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

A

conductor must from a closed loop

or…

be part of a competere circuit

20
Q

how is the generator effect used to generate different types of currents?

A

IN AN ALTERNATOR
to produce alternating current

IN A DYNAMO
to produce direct current

21
Q

describe the makeup of a basic transformer

A

a primary coil and a secondary coil of wire wrapped around an iron core

22
Q

why is iron used as the core for a transformer?

A

iron is easily magnetised

23
Q

explain how transformers work

A
  • an alternating current flows through the primary coil
  • this induces a changing magnetic field in the core
  • this changing magnetic induces a current to flow in the secondary coil
24
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

25
Q

describe the direction of the magnetic field produced by an induced current?

A
  • the direction of the field opposes the change that induced the current
  • the change is either the movement of the conductor or a change to the field
26
Q

what electromagnetic effect does a microphone take advantage of and how?

A
  • the generator effect
  • converts pressure variations in sound waves into an alternating current in a circuit
27
Q

how do loudspeakers make use of the motor effect?

A

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

28
Q

explain how loudspeakers work

A
  • current passes through coil
  • generating a magnetic field
  • magnetic field of the coil interacts with the magnetic field of the permanent magnet
  • this produces a resultant force
  • causing the cone to move
  • when the current switches direction, the direction of the force on the wire reverses
  • generation sound waves
29
Q

how is the pitch from a loudspeaker changed?

A
  • the frequency of the a.c current is altered
  • this creates a different frequency of vibration in the cone
30
Q

why must current flowing through a transformer be alternating?

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
31
Q

what can be said about a 100% efficient transformer?

A

the electrical power input equals the power output

32
Q

explain how a moving-coil loudspeaker produces a sound wave

A
  • current creates a magnetic field around the coil…
    … which interacts with the magnetic field….
    … producing a resultant force, causing the coil to move
  • when the direction of the current reveres, the direction of the resultant force reverses (producing a sound wave)
33
Q

explain why an alternating current is induced in a coil, when rotated

A
  • the coil moves through the magnetic field
  • a potential difference is induced across the coil
  • there is a complete circuit, so a current is induced
  • every half turn, the potential difference reveres direction
  • so every half turn, the current changes direction
34
Q

suggest the purpose of slip rings

A
  • provide a continuous connection between the transformer and the coils
  • prevents wires from twisting together
35
Q

what is the function of a microphone?

A

to convert the pressure variations in sound waves into variations in current

36
Q

explain how a moving-coil microphone works

A
  • sound waves cause the diaphragm to vibrate
  • the diaphragm causes the coil/ wire to vibrate
  • the coil/ wire move through the magnetic field
  • a potential difference is induced across the ends of the coil / wire
37
Q

why does an alternator produce alternating current?

A

the two sides of the coil are attatched to different rings

38
Q

why does the movement of the magnet induce a potential difference across the coil?

A

the magnetic field across the coil changes

39
Q

describe the potential difference in a step-down transformer

A

the potential difference is GREATER in the PRIMARY COIL

40
Q

describe the potential difference in a step-up transformer

A

the potential difference is GREATER in the SECONDARY COIL

physics paper 2 🎀 (4 decks)

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