SP12- Magnetism And The Motor Effect + SP13 Electromagnetic Induction

Question 1

What’s a permanent magnet

Answer 1

Eg a bar magnet - it’s always magnetic

A magnet can attract magnetic materials which include steel nickel and cobalt

Question 2

What’s the magnetic field

Answer 2

The space around a magnet where it can attract these materials

Question 3

What’s a bar like

Answer 3

It has 2 ends, one called a north seeking pole and one called a south seeking pole, if two magnets are placed close to each other, the North Pole on one will attract south on other, 2 north’s or 2 south’s will repel

Question 4

What’s an induced magnet

Answer 4

When a piece of magnetic material is in a magnetic field it becomes a magnet itself

It stops being magnetic when it’s taken out of the field

Question 5

Where are magnets used

Answer 5

Electric motors, generators, loudspeakers and other electrical devices

Used in simpler things - door latches and knife holders

Question 6

How can the shape of a magnetic field be found

Answer 6

Using plotting compasses - use lines that show how a single North Pole would move north to South

Question 7

How do plotting compasses work

Answer 7

The needle is a very small magnet, it always points to a position near the earths North Pole, a magnet suspended on a string will tilt relative to the horizontal by different amounts in different places

Compass needles are weighted at one end to keep them level

Question 8

What do we think the earths magnetic field is like

Answer 8

Similar to the shape of a magnetic field of a bar magnet, field thought to be caused by electric currents in the molten outer core made from a mix of iron and nickel

Question 9

What’s electromagnetism

Answer 9

A current flowing through a wire causes a magnetic field, electric motor and many other devices depend on the magnetic effect of electric currents

Question 10

What does the direction of the magnetic field depend on In electromagnetism

Answer 10

Depends on the direction of the current - of Current direction changes so does the direction of the magnetic field

Question 11

How does the right hand rule work

Answer 11

If you point right thumb in direction of the current from + to -, the magnetic field goes in the direction your fingers are pointing

Question 12

The stronger the current the ______ the magnetic field

Answer 12

The stronger the field - field is strongest closer to the wire and gets weaker further away

Question 13

What’s a solenoid

Answer 13

When a wire is made into a coil - the magnetic fields of all different parts of the wire form an overall magnetic field, the fields from individual coils add together form a very strong field inside the solenoid, on the outside - the fields from one side tend to cancel the fields from the other to give a weaker field outside

Question 14

What’s an electromagnet

Answer 14

A coil of wire with a current flowing through it

The magnetic field of an electromagnet can be made stronger by putting a piece of iron (an iron core) inside the coil

The iron becomes a temporary magnet - it’s only magnetic whilst the field from the electromagnet is affecting it

Question 15

What is the motor effect

Answer 15

A wire carrying a current experiences a force when it’s placed between 2 magnets - the current in the wire creates a magnetic field around the wire and this interacts with the magnetic field between the magnets

The force is greatest when the wire is at right angles to the magnetic field produced by the magnets and is 0 when the wire is in the same direction as magnetic field

there is an equal and opposite force on the magnets

Question 16

In the motor effect when is force greatest and least

Answer 16

The force is greatest when the wire is at right angles to the magnetic field produced by the magnets and is 0 when the wire is in the same direction as magnetic field

Question 17

What does Flemings left hand rule mean

Answer 17

Shows the directions of current force and magnetic field are related in the motor effect

Question 18

What’s magnetic flux density

Answer 18

The strength of the magnetic field - measured in Newton’s per amp metre (N/A m) or Tesla T)

Question 19

How is force caulcuated

Answer 19

F = B x I x L

Question 20

How does an electric motor use the motor effect

Answer 20

The force on a conductor in a magnetic field is used to cause rotation in electric motors

Search up a diagram!!

Question 21

What’s a electric motor like? - name some aspects

Answer 21

There’s a magnet - north side pushes coil up and south side down so it rotates about a pivot

Carbon brushes then make electrical contacts between the circuit and motor

There’s a metal split ring commutator - it’s split so the current changes every half turn to keep it rotating

Question 22

How does the split ring commutator work

Answer 22

It ensures that the force on the coil always turns it in the same direction

Commutator ensures that the current is always flowing in the correct direction to make the coil continue to spin

Question 23

How can a voltage be induced in magnetism

Answer 23

A changing magnetic field can induce a voltage or PD in a wire that causes a current to flow

A PD can also be induced if a wire is moving in a magnetic field

Wire often made into coil so there is more wire in the changing magnetic field

Question 24

In induced voltage, what does the wise of the induced potential difference depend on

Answer 24

Depends on the number of turns in a coil of wire, strength of the magnetic field, how fast the magnetic field changes or moves Past the coil

Reversing direction of change reverses the direction of the induced potential difference
I

If the PD causes a current to flow, the magnetic field of the current opposes the original change

Question 25

Tell me what happens when a magnet is moved through a loop of wire

Answer 25

Magnet and magnetic field is moving to the right in this example

Potential difference is induced in wire which causes a current to flow

Magnetic field around wire in opposite direction to original change - don’t really know what that means lol but that’s what it says hahaahah

Question 26

What does a generator consist of

Answer 26

Consists of a coil of wire that is rotated inside a magnetic field - as the coil turns, a voltage is induced in the wire

Slip rings - ends of the coil are connected to this

Electrical contact with an external contact is made using carbon brushes which press on slip rings

Produces alternating current so called an alternator

Question 27

What current does an alternator make

Answer 27

Alternating current

Question 28

What’s a dynamo

Answer 28

Many appliances neee direct current - a commutator switches connection ever half turn of the coil so produces a form of direct current

A generator with a commutator is often called a dynamo

Question 29

What do microphones do

Answer 29

Concert the pressure variations in sound waves into variations in current in electrical circuits

Question 30

Tell me the steps of what a microphone does

Answer 30

Sound waves cause variations in air pressure

The pressure variations make a diaphragm vibrate

The diaphragm moves a coil of wire backwards and forwards - coil is around a permanent magnet so a current is induced

Question 31

How does a loud speaker work

Answer 31

It converts variations in an electrical current into sounds waves

Loud speakers have similar components to a microphone - varying current through a coil in a magnetic field causes a force on the coil - which moves backwards and forwards as the current varies

The coil is connected to a diaphragm and the movements of the diaphragm produces sound waves

Question 32

What’s the national grid

Answer 32

A system of wires and cables supplying electricity

Question 33

Where do wires get very hot in the national grid

Answer 33

Energy waster by heating inside buildings is quite small but the amount is significant for transmission lines

Question 34

How are current and pd changed in the national grid by transformers

Answer 34

If pd is increased - current is decreased

When current is smaller, less energy is transferred by heating and efficiency is improved

Power stations produce electricity at25kV and transformers change this to 400kV before its sent round the country - voltage revised when sent to other factories and buildings

Question 35

What does a step up transformer do

Answer 35

Increases the voltage and decreases the current at the same time

Question 36

What does a step down transformer do

Answer 36

Makes the voltage lower and the current higher

Question 37

How is a transformer made

Answer 37

Using 2 coils of insulated wire wound on to an iron core - there’s NO electrical connection between the two coils of wire

Question 38

What type of current do transformers need

Answer 38

An alternating current - when the direction of pd and current changes many times each second - the alternating current in the primary coil creates a continuously changing magnetic field and the iron core of the transformer carries this magnetic field to the secondary coil

Question 39

What does the changing magnetic field do the the secondary coil

Answer 39

Induces a changing potential difference in the secondary coil - potential difference is greater in the secondary coil if it has more turns thag the Primary

Question 40

What’s the equation for working out the potential differences across the coils of a transformer can be worked out using this equation:

Answer 40

V(lower left p/ V(LL s) = N (LL p) / N (LL s)

N = number of turns in the coil

Question 41

What’s potential difference

Answer 41

A measure of energy transferred by each coulomb of charge that flows through a wire - current measured the number of coulombs per second

Question 42

How is the power calculated

Answer 42

P = I x V

Question 43

What 2 things multiply to the same thing and why in transformers

Answer 43

Energy can’t be created or destroyed so power supplied in primary coil must be equal to the secondary if it’s 100% efficient

V(lower left P) x I(LL p) = V(LL s) x I(LL s)