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Physics IGCSE > Magnets & Magnetism > Flashcards

Magnets & Magnetism Flashcards

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1
Q

what is a magnetic field

A

a field where magnetic materials experience a force

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2
Q

magnetic poles attraction and replusion

A

north - north = repulsion
south - south = repulsion
north - south = attraction

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3
Q

what do magentic field lines show

A

Magnetic field lines provide a visual representation of the magnetic field in a given space through use of arrows to show direction.
They also show the strength of the field through the distance of the lines (closer together = stronger/closer field).
And the shape of the field

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4
Q

how to see magnetic field patterns with iron filings

A

place a peice of paper ontop of a bar magnet
sprinkle iron filings ontop of the paper
gently tap the paper to allow the iron filings to settle on the field lines

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5
Q

how to see magnetic field lines with a compas

A
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6
Q

what is induced magnetism

A

When a magnetic material is placed in a magnetic field, the material can temporarily be turned into a magnet.

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7
Q

why can induced magnitism not produce repulsion

A

because the induced poles are always in the same order as the first magnet. Hence it is not possible for like poles to be facing each other

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8
Q

how do magnetic domain explain induced magnetism

A

When the domains are pointing in random direction each little magnetic field cancels out its neighbours and the metals will not be magnetic. When external magnetic field is applied the domains line up and reinforce each other (magnetism has been induced)

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9
Q

what are the 4 magnetic materials

A

iron
nickel
cobalt
steel

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10
Q

what is magnetically soft and what are the materials which are soft

A

Magnetically soft materials lose their magnetism (iron/cobalt)

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11
Q

what is magentically hard and what are the materials which are hard

A

Magnetically hard materials retain their magnetism (steel)

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12
Q

how can you use 2 permanent magnets to produce a uniform magnetic field patter

A

A uniform field is created when two opposite poles are held close together. Magnetic fields are always directed from North to South.

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13
Q

what do electromagnets consist of

A

a power supply, coil (solenoid) and a Iron core

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14
Q

describe and draw the magnetic field around a straight wire

A

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

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15
Q

describe and draw the magnetic field around a flat circular coil

A

similar to the magnetic field of a bar magnet
there are concentric ellipses of magnetic fiele lines around the coil

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16
Q

describe and draw the magnetic field around a solenoid

A

strong and uniform
outside the coil the field is just like a bar magnet’s field
the ends of a solenoid act like the north pole and south pole of a bar magnet

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17
Q

how does a force effect charged particles in a wire

A

it can push electrons along the wire, causing current to flow.
or it can can induce forces that move the wire

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18
Q

what is flemmings left hand rule used for

A

which way the force acts

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19
Q

describe flemmings left hand rule

A

First finger - field
seCcond finger - current
thuMb - force/motion

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20
Q

what are 4 factors which will speed up the induced potential difference

A

The speed at which the wire, coil or magnet is moved
The number of turns on the coils of wire
The size of the coils
The strength of the magnetic field

21
Q

how does a loudspeaker work

A

An alternating current is fed into a coil, generating an alternating electromagnetic field.
This produces a magnetic force which is continually changing direction.
The coil is connected to a cone which will vibrate and produce a sound.

22
Q

what is a simple dc motor

A

DC motors consist of a coil of wire in betweeen two permanent magnets. Direct current flows through the wire and it experiences a turning effect due to the forces exerted on it in the magnetic field. As the current flows in opposite directions on each side of the coil, the forces on each side are in opposite directions making it turn

23
Q

what does the permenate magnets in a dc motor do

A

they create a steady magnetic field

which induces and intereacts with the megnetic field of the current

which induces the coil creating a force and motion

24
Q

what does the current in the wire do in a simple dc motor

A

take electrical power through direct current, and convert this energy into mechanical energy causing it to rotate

25
Q

how does a simple dc motor work

A

current flows through the coil through the positive terminal and out through the negative terminal producing a magnetic field of clockwise forces (as it is inbetween 2 permenate magnents)
because both sides of the coil produce a different force the wire will rotate clockwise 90 degrees and then rotate again 90 degrees but anticlockwise
this is not practicle so you add a split ring communtator to change the direction of the current every half turn
this process continues and so the simple dc motor will turn 360 degrees

26
Q

what is electromagnetic induction

A

the creation of voltage in a wire which is experiencing a change in magnetic field

27
Q

how is electromagetic induction done

A

by an electrical conductor movin through a magnetic field
the magnetic field changes through a electrical conductor

28
Q

how can the size of the magnetic force be increases

A

increase the turns to the coil
have a stronger external magnetic field
increase the electrical current

29
Q

what is the motor effect

A

A current carrying wire creates a magnetic field. it can interact with another magnetic field, causing a force that pushes the wire at right angles

30
Q

what is a simple AC generator

A

a simple ac generator converts kinetic energy into alternating current (AC) electricity.
it is based on the principle of electromagnetic induction
by the coil rotating + an interaction with the mgnetic field it induces a current in the coil

31
Q

how can ac be produces

A

when a coil rotates in a magnetic field
when a magnet rotates within a coil

32
Q

what is a split ring cummutator

A

it swaps the positive and negative connections every half turn
this means the direction of current swaps every half turn causing the forces acting on the coil to always be in the same direction

33
Q

what is a transformer

A

changes the size of voltage of an alternating current
it is acheived using the generator effect

34
Q

what is the structure of a transformer

A

a primary coil
a secondary coik
an iron core

35
Q

why is iron used in a transformer

A

because it is easily magnetised

36
Q

how does a transformer work

A

they have 2 coils - primary and secondary along with an iron core
when alternating voltage is applied across the primary coil the magnetically soft iron core magnetises and demagnetises quickly
this induces an alternating voltage in the secondary coil

37
Q

what is a step up transformer

A

The size of the voltage INCREASES from the primary to the secondary
there will be more turns in the secondary coil

38
Q

what is a step down transformer

A

The size of the voltage DECREASES from the primary to the secondary
there will be more turns on the primary than secondary

39
Q

what is a step up transformer used for

A

step up transformers are used for transmission in power lines which recues power loss

40
Q

what is a step down transformer used for

A

a step down transformer is used in homes to keep us safe

41
Q

how can you calculate transformers

A

priamry voltage/secondary voltage = number of turns on primary/number of turns on secondary

42
Q

if a transformer is 100% efficient then what is the relation between input and output power

A

input power = output power

43
Q

equation for is a transformer is 100%

A

.

44
Q

what do transformers only work with

A

AC electricity

45
Q

what happens to the current if the voltage rises from the primary to the secondary coil

A

the current drops

46
Q

what is the national grid

A

a system or cables and transformers linking power stations to consumers (houses, buildings and factories)

47
Q

what is the problem with transporting high current

A

there is lots of heat becuase of the resistance which means you loose loads of energy

48
Q

how does the national grid work

A

increase the voltage in the energy power station by using a step up transformer
wires then transmit the electrivity all around the country
just before it reaches its destination (a certain town) the voltage has to be reduced back down by a step down transformer

Physics IGCSE (7 decks)

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