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GCSE Physics > 6. Magnetism & electromagnetism > Flashcards

6. Magnetism & electromagnetism Flashcards

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1
Q

what do magnets do

A

repel and attract other magnets and attract magnetic substances

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2
Q

what are the properties of magnetically hard materials

A

magnetically hard = keeps induced magnetism permanently

eg. steel

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3
Q

what are the properties of magnetically soft materials

A

magnetically soft = loses its induced magnetism quickly

eg. iron

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4
Q

definition of magnetic field line

A

(lines of force ) used to show the size and direction of magnetic fields

always point from north to south

the closer together the lines the stronger the force

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5
Q

when some materials are placed in a magnetic field what happens

A
  1. magnetism is induced = magnetic materials are brought into a magnetic field = material acts as a magnet
  2. this magnetism has been induced by the original magnet
  3. the closer the magnet and magnetic material get= the stronger induced magnetism will be
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6
Q

definition of uniform magnetic field line

A

created by placing the N and S of 2 permanent bar magnets near each other

magnetic filed line = same distance apart from each other

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7
Q

name 2 methods which can be used to see magnetic field patterns

A

using multiple compasses
iron filings

both align themselves with magnetic fields

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8
Q

how do you use iron filings to see a magnetic field

A
  1. put magnet(s) under piece of paper
  2. scatter iron filings on top
  3. tap the paper until iron filings form a clear a pattern
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9
Q

what does an electric current in a conductor do

A

produce a magnetic field round it

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10
Q

PAPER 2

describe the construction of electromagnets

A

???

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11
Q

PAPER 2

describe magnetic field pattern for a straight wire

( need to be able to draw )

A

field made up of concentric circles with the wire in the centre

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12
Q

PAPER 2

describe magnetic field pattern for a flat circular coil

(need to be able to draw)

A
  1. magnetic field in centre of flat circular coil of wire = similar to bar magnet
  2. concentric ellipses ( stretched circles ) of magnetic field lines around the coil
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13
Q

PAPER 2

describe magnetic field pattern for a solenoid

(need to be able to draw)

A
  1. field inside = strong + uniform
  2. field outside = like bar magnet
  3. = ends of solenoid act like the north + south pole of a bar magnet
  4. this type of magnet = electromagnet
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14
Q

PAPER 2

when is there a force on a charged particle ( electrons in current )

A

when it moves in a magnetic field as long as its motion is not parallel to the field

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15
Q

PAPER 2

what happens to charged particles ( electrons in current ) moving through a magnetic field

A

will experience a force

as long as they are not moving parallel to the field lines

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16
Q

why is a force exerted on a current- carrying wire in a magnetic field

A

??? wire is at 90* to magnetic field ( if wire runs along magnetic field wont experience any force at all )

17
Q

which direction does force always act in on a current- carrying wire in a magnetic field

A

force always acts in same direction relative to the magnetic field of the magnets + the direction of the current in the wire

18
Q

how does a current-carrying wire in a magnetic field work in a simple d.c electric motor

A

??? need to ask teacher

19
Q

definition of motor effect ( place a current-carrying wire in a magnetic field )

A
  1. current-carrying wire is put between magnetic poles
  2. the 2 magnetic fields affect one another
  3. result = force on the wire
  4. = cause wire to move
20
Q

how does a loud speaker work ( in terms of the motor effect )

A
  1. a.c electrical signals from an amplifier = fed to coil of wire in speaker ( which is wrapped round the base of a cone
  2. coil = surrounded by permeant magnet = a.c signal cause force on the coil= moves back and forth
  3. movements = cone vibrate = sound
21
Q

how to do you use Fleming’s left hand rule to predict the direction of the resulting force when a wire carries a current perpendicular to a magnetic field

A
  1. use left hand
  2. point First finger in the direction of the Field
  3. point seCond finger in direction Current
  4. = thuMb will the point in the direction of the force ( Motion )
22
Q

how does the force on a current- carrying conductor in a magnetic field change with magnitude and direction of the field and current

A

??? if direction of movement is reversed = induced voltage / current will be reversed to

23
Q

when is voltage induced in a conductor or a coil

A
  1. when it moves through a magnetic field

2. when a magnetic changes through it

24
Q

what happens when a conductor or a coil moves through a magnetic field or when a magnetic field moves through it

A

a voltage is induced

25
Q

what factors effect the size induced voltage

  • how do you get a bigger induced voltage
A
  1. strength of magnet
  2. number of turns on the coil
  3. speed of movement
26
Q

how is electricity generated by the rotation of a magnet within a coil

OR
rotation of a coil within a magnetic field

(eg. explain how a.c generators work)

A
  1. generators rotate a coil in a magnetic field / (magnet in a coil )
  2. coil spins = current induced = changes direction every half turn
  3. a.c generators have slip rings + brushes ( instead of split ring commutator ) = contacts don’t swap every half turn
  4. = produce a.c voltage
27
Q

how do you increase the voltage in terms of a generator and producing electricity

A

faster revolutions = produce more peaks + high voltage

28
Q

PAPER 2

what does a transformer do

A

changes the size of an alternating voltage by having different numbers of turns on the input and output sides

29
Q

PAPER 2

describe the structure of a transformer

A

has 2 coils, the primary and the secondary, joined with an iron core

30
Q

PAPER 2

in transformers what happens when an alternating voltage is applied across the primary coil

A

the magnetically soft (iron) core magnetises and demagnetises quickly = induces an alternating voltage in the secondary coil

31
Q

PAPER 2

in transformers what is the ration between the primary and secondary voltages the same as

A

the ratio between the number of turn on the primary and secondary coils

32
Q

PAPER 2

what does a step- up transformer do and why

A

increases the voltage

have more turns on the secondary coil than the primary coil

33
Q

PAPER 2

what does a step- down transformer do and why

A

decreases the voltage

have more turns on the primary coil than on the secondary coil

34
Q

PAPER 2

how are step-up and step-down transformers used on a larger scale

A

used when transmitting electricity across the country ( make transmitting main electricity more efficient )

35
Q

PAPER 2

why are step-up and step-down transformers used on a larger scale ( in terms of mains electricity )

A
  1. voltage produced by power station = too low to to be transmitted effeiclently
  2. low voltage = higher the current = cause wires to heat up
36
Q

PAPER 2

how step-up and step-down transformers make transmitting mains electricity more efficient

A
  1. step-up transformer = boost the voltage before its transmitted
  2. step-down transformer = used at end of journey = reduce voltage= more useful + safer to use
37
Q

PAPER 2

what is the relationship between input ( primary ) and output ( secondary) voltages and the turns ratio for a transformer

give equation

A

input (p ) voltage / output (s) voltage = primary turns / secondary turns

38
Q

PAPER 2

what is the formula for power supplied in transformer

A

Power = Voltage x Current

P= VI

39
Q

PAPER 2

what is the relationship between input power and output power of a transformer ( for 100% efficiency )

give equation

A

input power = output power

V(p) I(p) = V(s) I(s)

GCSE Physics (8 decks)

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