Magnets & Magnetism

Question 1

what is a magnetic field

Answer 1

a field where magnetic materials experience a force

Question 2

magnetic poles attraction and replusion

Answer 2

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

Question 3

what do magentic field lines show

Answer 3

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

Question 4

how to see magnetic field patterns with iron filings

Answer 4

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

Question 5

how to see magnetic field lines with a compas

Answer 5

Question 6

what is induced magnetism

Answer 6

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

Question 7

why can induced magnitism not produce repulsion

Answer 7

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

Question 8

how do magnetic domain explain induced magnetism

Answer 8

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)

Question 9

what are the 4 magnetic materials

Answer 9

iron
nickel
cobalt
steel

Question 10

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

Answer 10

Magnetically soft materials lose their magnetism (iron/cobalt)

Question 11

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

Answer 11

Magnetically hard materials retain their magnetism (steel)

Question 12

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

Answer 12

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

Question 13

what do electromagnets consist of

Answer 13

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

Question 14

describe and draw the magnetic field around a straight wire

Answer 14

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

Question 15

describe and draw the magnetic field around a flat circular coil

Answer 15

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

Question 16

describe and draw the magnetic field around a solenoid

Answer 16

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

Question 17

how does a force effect charged particles in a wire

Answer 17

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

Question 18

what is flemmings left hand rule used for

Answer 18

which way the force acts

Question 19

describe flemmings left hand rule

Answer 19

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

Question 20

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

Answer 20

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

Question 21

how does a loudspeaker work

Answer 21

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.

Question 22

what is a simple dc motor

Answer 22

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.

Question 23

what does the permenate magnets in a dc motor do

Answer 23

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

Question 24

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

Answer 24

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

Question 25

how does a simple dc motor work

Answer 25

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

Question 26

what is electromagnetic induction

Answer 26

if a wire is moved into a magnetic field at right angles a voltage is induced

Question 27

how is electromagetic induction done

Answer 27

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

Question 28

how can the size of the magnetic force be increases

Answer 28

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

Question 29

what is the motor effect

Answer 29

a wire carrying current experiences a temporary magnetic field the temporary magnetic field interacts wit hthe permenate magnetic field of the bar magnets this creates a force which moves a wire

Question 30

what is a simple AC generator

Answer 30

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

Question 31

how can ac be produces

Answer 31

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

Question 32

what is a split ring cummutator

Answer 32

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

Question 33

what is a transformer

Answer 33

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

Question 34

what is the structure of a transformer

Answer 34

a primary coil a secondary coik an iron core

Question 35

why is iron used in a transformer

Answer 35

because it is easily magnetised

Question 36

how does a transformer work

Answer 36

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

Question 37

what is a step up transformer

Answer 37

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

Question 38

what is a step down transformer

Answer 38

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

Question 39

what is a step up transformer used for

Answer 39

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

Question 40

what is a step down transformer used for

Answer 40

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

Question 41

how can you calculate transformers

Answer 41

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

Question 42

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

Answer 42

input power = output power

Question 43

equation for is a transformer is 100%

Answer 43

.

Question 44

what do transformers only work with

Answer 44

AC electricity

Question 45

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

Answer 45

the current drops

Question 46

what is the national grid

Answer 46

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

Question 47

what is the problem with transporting high current

Answer 47

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

Question 48

how does the national grid work

Answer 48

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