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gcses > physics topic 7 > Flashcards

physics topic 7 Flashcards

1
Q

what are the poles of a magnet

A

Where magnetic forces are strongest.

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2
Q

what are permanent magnets

A

they produce their own magnetic fields. Can attract and repel.

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3
Q

what are induced magnets

A

Material that becomes magnetic when placed in a magnetic field.
Induced magnets can only attract.

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4
Q

give examples of metals that are magnetic

A

Iron, steel, nickel and cobalt

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5
Q

what is a magnetic field

A

The region around a magnet where a force acts on another magnet (or magnetic material).

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6
Q

describe the direction of a magnetic field

A

The direction of a magnetic field line is always from north pole to south pole.

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7
Q

how can the magnetic field direction of a magnet be seen

A

Placing a magnetic compass in the magnetic field of a bar magnet causes the compass to point from north to south

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8
Q

how can the magnetic field shape of a magnet be seen

A

Place the bar magnet under a piece of paper and sprinkle iron filings over
the paper. Tapping the paper will produce the magnetic field pattern

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9
Q

how does a magnetic compass work

A

A magnetic compass contains a small
bar magnet which points in the direction of the Earth’s magnetic field.

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10
Q

what does the magnetic field pattern produced by compasses lead us to believe

A

Earth’s core is magnetic.

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11
Q

what is thought to be the origin of the earths magnetic core

A

movement of molten iron in the core.

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12
Q

what happens when a current flows through a conducting wire

A

a magnetic field is produced around the wire.

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13
Q

what does increasing the current flowing through an electromagnet do

A

increases the strength of the magnetic field.

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14
Q

what does Increasing the distance from the wire in an electromagnet do

A

decreases the strength of the magnetic field.

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15
Q

what is the right hand rule

A

Thumb points to direction of current
(+ to -)

Fingers curl to show direction of magnetic field

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16
Q

what is electromagnetism

A

When a current flows through a conducting wire a magnetic
field is produced around the wire.

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17
Q

what is a solenoid

A

a coil of wire

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18
Q

how can you increase the strength of an electromagnetic field

A

Have more turns on the COIL

Increasing the CURRENT

Have an IRON CORE

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19
Q

what is an electromagnet

A

A solenoid with an iron core is an electromagnet.

20
Q

what does a relay switch do

A

It uses a solenoid to attract an iron
armature

21
Q

why are relay switches used

A

Relays are used so that a
small current can turn on a
larger current in an isolated
circuit.

This reduces the amount of
thicker, more expensive,
wires needed.

22
Q

Explain how an ignition circuit
works.

A
  • closing the switch causes a current to pass through the electromagnet
  • the iron core (of the electromagnet) becomes magnetised
  • the electromagnet / iron core attracts the iron arm
  • the iron arm pushes the (starter motor) contacts together
  • the starter motor circuit is complete
  • a current flows through the starter motor (which then turns)
23
Q

describe how an electric bell works

A

Close Switch

Current flows through circuit

Making an electromagnet

Attracts iron strip (armature)

Causing hammer to hit gong

Circuit breaks

Electromagnet deactivates

Iron strip (armature) returns to original position

24
Q

describe what happens when you put a wire carrying a current in a magnetic field
(force on a conductor)

A

A wire carrying a current

Has a magnetic field around it (right hand thumb rule)

If you put this wire into ANOTHER magnetic field

The magnetic fields will interact with each other (attract and repel)

Causing the wire to MOVE

25
Q

what factors effect a force on a conductor

A

Magnetic Flux Density (B) in tesla

Current (I) in amperes

Length of Conductor (L) in
metres

26
Q

how are the factors that effects a force on a conductor linked in an equation

A

Force (N) = Magnetic flux density (T) x Current (A) x Length(m)

27
Q

when does the maximum force on a wire occur

A

Occurs when wire is perpendicular to the magnetic field Because it cuts through more of the magnetic field

28
Q

describe the motor effect

A

When a conductor carrying a current is placed in a magnet
field the magnet producing the field and the conductor exert a force on each other.

29
Q

describe Flemings left hand rule

A

THUMB = Direction of Force (motion)

INDEX FINGER = Magnetic field (N to S)

SECOND/MIDDLE FINGER = Current (+ to -)

30
Q

how do headphones and loudspeakers use the motor effect

A

Loudspeakers and headphones use the motor effect to convert variations in current in electrical circuits to the pressure variations in sound waves.

31
Q

how do speakers work

A

Alternating current creates a magnetic field around the coil

which interacts with the permanent magnet field

producing a force causing the coil/cone to move

Leading to vibrations which produces sound

when the direction of the current reverses, the direction of the force reverses

32
Q

what is a generator

A

If you move the coil of wire in a magnetic field it generates an induced current
(electricity)

33
Q

How to increase the size of the induced potential difference in a generator

A

Rotate coil faster

Stronger magnetic field

Increase number of turns of wire on coil

34
Q

what is the Direction of Induced
Potential difference in a generator dependant on

A

dependent on the direction of rotation of the coil and the orientation of the magnetic
field.

35
Q

what does Reversing the direction of rotation of the coil in a generator do

A

will reverse the direction
of the induced potential difference/induced current.

36
Q

what does Swapping the polarity of both magnets do in a generator

A

will reverse the direction
of the induced potential difference/induced current.

37
Q

describe how Generators/Alternators work

A

Alternators rotate a coil through a magnetic field

This induces a potential difference

As there is a complete circuit, a current is induced

Generators have a slip-ring commutator – allows coil to always remain in contact to the circuit

This induces an alternating current in the coil

Every half turn, the current and potential difference reverses direction (A.C)

38
Q

describe how Dynamos work

A

Dynamos rotate a coil through a magnetic field

This induces a potential difference

As there is a complete circuit, a current is induced

Dynamos have a split-ring commutator –the two ends of the coil swap from one
brush to the other

so the direction of the induced current does not reverse every half rotation (D.C)

39
Q

what angle should wire be to get max voltage in alternator and dynamo outputs

A

90 degrees

40
Q

how do microphones work

A

Pressure from sound waves

Causes the diaphragm to vibrate

Which causes the coil to vibrate

Coil moves through the magnetic field

Which induces a potential difference
and current

41
Q

why is the core of an electromagnet iron

A

because iron is quickly magnetised

42
Q

describe step up transformers

A

Increase the potential difference so Vs > Vp

More turns on the secondary coil

43
Q

describe step down transformers

A

Decrease the potential difference so Vs < Vp

More turns on the primary coil

44
Q

how do transformers work

A

insulation prevents electricity/current flowing through the iron core

alternating current (a.c) in the primary coil

produces a changing magnetic field in the iron core

Which produces magnetic field in the secondary coil

induces an alternating potential difference across the secondary coil

and therefore an alternating current (a.c) in the secondary (coil)

45
Q

how are transformer used in the national grid

A

to make the transmission
of electricity more efficient.

46
Q

what does increasing the potential difference do to overhead power lines

A

decrease the current in the
overhead powerlines.

47
Q

Potential difference and current are what

A

inversely proportional

gcses (19 decks)

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