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Physics Year 11 > Electromagnetism > Flashcards

Electromagnetism Flashcards

(58 cards)

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1
Q

What are permanent magnets made from

A

Steel , retains its magnetism after being magnetised

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2
Q

What is iron useful for

A

Magnetically soft loses magnetism easily useful for tenpirarj magnets

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3
Q

The closer field lines are together …

A

The stronger the magnetic field

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4
Q

How can you induce magnetism

A

Domains line up , by leaving the magnetic material in a magnetic field can also happen if steel is left in one position , the earths magnetic field induces magnetism on it

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5
Q

Where do arrows face on a north side

A

Outwards

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6
Q

What are magnetic fields

A

Volume of space where magnetism can be detected it can’t be seen but iron filings or plotting compases shows its shape

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7
Q

What happens when a current flows through a conductor (wire )

A

A magnetic field is created around the wire - electromagnetism

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8
Q

What is the field like around a straight wire

A

Weak and circular direction can be found using the right hand grip rule

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9
Q

How can you increase the strength of the electromagnet

A

Increasing the current in the wire
Wrapping the wire into a coil (solenoid)
Increasing the current in the solenoid
Increasing the number of turns on the solenoid
Wrapping the solenoid around a soft iron core - solenoid and soft iron core is referred to as an electromagnet
Use right hand grip rule to work out the positions of the poles - fingers curl in the direction of the current and the thumb points to the North Pole of the solenoid

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10
Q

A slolenoid with an alternating current would be ….

A

Demangentizing

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11
Q

What safety precautions should you take with an electromagnet

A

Beware of wire getting too hot and electrocution of the bare wires

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12
Q

What is a magnetic field

A

A region in space where magnetic materials experience a force

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13
Q

How does an electric bell work

A

When the bell is pushed circuit is complete and current flows . The electromagnet is magnitized and attracts the iron armature . When the armature moves the hammer strikes the bell creating a gap at the contact screw so the circuit is incomplete and current stops flowing . The electromagnet is now off and the springs armature returns to its original position the circuits complete and the process repeats

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14
Q

How does a circuit breaker work

A

If the currents to High the electromagnet becomes strong enough to pull the iron catch out of position so the contacts open and the circuit breaks. Once the problems been corrected the catch is reset by pushing the reset button

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15
Q

How does a relay switch work

A

Large current flows circuit means danger of electric shock to the user so relay switches use a small current in one circuit to turn on a second circuit that may be carrying a much larger current. Switching on the low voltage supply magnetised the elctromagnet which attracts the pivot which pushes the springy contacts of the voltage supply together , completing the circuit

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16
Q

How does a loudspeaker work

A

An electric signal is passed through a coil held in a magnetic field from a permanent magnet , the coil becomes an electromagnet its strength varying with the current a varying forces occurs between the electromagnet and the permanent magnet this makes the coil move backwards and forwards to the same pattern as the electrical signal the coil moves a paper cone in and out the moving paper cone makes the air vibrate creating sound waves

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17
Q

What happens if a wire is moved in a magnetic field

A

When a conductor carries a current in a magnetic field it experiences a force . The magnetic field from the permanent magnet combines with the magnetic field around the conductor to produce a force . The direction of the force is at right angles to both the field and the current . It doesn’t work if the field is parrel to the current it only works if the wire is at right angles to the magnetic field

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18
Q

What affects the size of force

A

Size of current strength of magnetic field and number of loops of wire

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19
Q

What affects the direction of the force

A

Direction of current

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20
Q

What causes the motor effect

A

In certain places the magnetic field of the current and the permanent field are in the same direction , reinforce each other and give a stronger magnetic field in other places they are in the opposite direction and produce a weak field . The wire is pushed from the strong part of the field to the weak part of the field known as the motor effect

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21
Q

What does thumb mean

A

Motion

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22
Q

First finger

A

Field direction n to s

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23
Q

Second finger

A

Current

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24
Q

Where did signals in a loudspeaker come from

25
How does a motor work
When a current flows through a coil the left side is pushed up and the right side down. When the coil is vertical the forces can't turn it any further as there is no torque so the split ring commutator swaps the brushes so the current changes direction so the wire at the bottom is pushed up and the wire at the top is pushed down and the loop keeps turning .
26
What does the split ring commutator do
Swaps the brushes every half turn in an electric motor
27
How are the brushes held against the commutator
By springs
28
How do you increase the speed of the motor
Increase number of turns of wire Increase strength of the magnetic field Increase the current flowing through the loop of wire Put a iron core in the coil
29
What do generators do
Make electricity from Movement
30
What happens if a wire is moved in a magnetic field at right angles
Field lines are cut and voltage is induced in the wire , if the wire is part of a complete circuit current will flow . It is called the dynamo effect and electromagnetic induction . When the wire stops moving or is moved sideways there's no voltage nor current
31
How do you increase induced voltage from living a wire across a magnetic field at right angels
By moving the wire faster and using a stronger magnet
32
What happens if you push a magnet into a coil
Electrons are given a push by the magnetic field inducing a voltage and a current flow . If the magnet stops moving there's no voltage or current
33
How do you have higher voltage in the coil
Move the magnet faster , use a stronger magnet and put more turns on the coil
34
What is fardays law
The size of the induced voltage across the ends of a wire is directional proportional to the rate at which the magnetic lines of flux are being cut
35
What happens if the direction of motion is reversed in electromagnetic induction
The direction of induced current is reversed
36
How do bicycle generators work
Small generator used to generate electricity for a bicycle light as the cyclist pedals the wheel rotates and a small magnet within the generator sound around and it's field cuts through the surrounding coil inducing a current user to work the cyclist lights
37
How do alternators work ( bulb)
Stronger than bicycle generator because they use stronger magnets and have more turns of wire on their coil and spin their coil faster . The coil rotates between the piles of a magnet and has slip rings that are fixed to the coil and Turk with it . The brushes (2 carbon contacts ) rub against the slip ring so the coil is connected to the bulb.when the coil rotates its wires cut through the magnetic field lines inducing a current in the bulb . As the coil rotates each side travels up and then down so the current flows one way then the opposite way so it's alternating current .
38
When is the current of the generator greatest
When the coil is horizontal as it cuts field lines most rapidly in this position . When the coil is vertical the current is zero as it doesn't cut any field lines in this position
39
How do you generate a higher current on the alternator
Use a coil with more turns and a stronger magnet and rotate the coil faster
40
What is the frecquency of an alternator
The number of complete cycles it makes each second . If it rotates twice in a second the frequency is 2Hz frequency = cycles over seconds
41
What are transformers
Devices used to change voltage
42
How do transformers work
As the size of a current in a coil increases the magnetic field grows . If a second coil is placed near the first coil a changing magnetic field will las through it and cut through the wires of the second coil inducing a voltage across that coil . The size and direction of the induced voltage changes as the voltage applied to the first coil changes .
43
What are the two types of transformers
Step up - output voltage higher than input voltage | Step down - output voltage lower than input voltage
44
What is the equation for a transformer
Input voltage ------------- Output voltage. = number of Turns on primary coil -------------------- Number of turns on secondary
45
What happens if a transformer is 100% effective
Power in = power our Primary voltage x primary current = secondary voltage x secondary current
46
Why are transformers used in the national grid
As current passes through the wire of the national grid energy is lost by heat . If current flow is kept to a minimum heat loss is reduced so transformers are used in the national grid to transmit electricity at low current and high voltage
47
What is the national grid
Network of wires and cable that carry electrical energy from power station to consumers
48
What happens in the national grid
Gas or coal is burned in air in power station , water is heated to make steam which turns a turbine which turns a generator which produces AC electricity.. the voltage is stepped up to 400KV by a transformer to reduce the current . High voltage is v dangerous so cables are supported high above ground on pylons and as they eneter cities are buried underground . Close to where the electrical energy is needed it's passed through a step down transformer to decrease the voltage to 230 V and increase the current .
49
What is transformers made up of
Primary coil around a soft iron core which is where the secondary coil is also wrapped around
50
What is alternating voltage
Where direction reverses and produces an alternating current
51
How does the commutator work on the motor
The bare wire touches the brushes but is not joined so as the coil turns the connections swap over every half turn reversing the current in the coil
52
How could you control sped of motor
Use a variable resistor in series with the coil to control the current
53
Why does a loop of wire with current passes through it move in a magnetic field
A current carrying wire in a magnetic field experience a force
54
What does a changing magnetic field in a coil of wired do
Induced a voltage
55
What happens if electrons in a bar are moving pararlel to the magnetic field
There will be no force
56
Why do motors stop rotating after 90 degree
Force on top arm acts upwards and the force on the bottom arm acts downwards so the forces oppose the rotation of the loop . By swapping current direction every 90 degrees the forces of the loop always act in a way that keeps it rotating
57
Why do transformers only work with ac
Beacuse of it was dc the current wouldn't change so the magnetic field in the primary coil wouldn't change so the magnetic field in the secondary coil wouldn't change so no voltage would be induced
58
How do headphones work
AC current flows through the coil of wire in the magnetic field of the permanent magnet so the coil of wire experiences a force. This causes the cone to move The AC current is constantly changing direction so the force on the coil is constantly changing so the cone vibrates back and forth. The vibrations caused the air vibrate and cause soundwaves

Physics Year 11 (4 decks)

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