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GCSE Edexcel Separate Physics > SC13 Electromagnetic Induction > Flashcards

SC13 Electromagnetic Induction Flashcards

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1
Q

Define electromagnetic induction

A

A voltage is induced in a conductor or a coil when it moves through a magnetic field or when a magnetic field changes through it

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2
Q

What is the difference between the motor effect and the generator effect?

A
  • In the motor effect, there is already a current in the conductor that experiences a force
  • whereas in the generator effect, there is no initial current in the conductor, but one is induced when it goes through the magnetic field
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3
Q

How can a current be induced in a wire?

A

If a wire is moved into a magnetic field, such that the field lines are cut, a potential difference is induced between the ends of the wire and a current can flow

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4
Q

How can we induce a voltage in a wire with coils?

A

We can move the magnet around it

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5
Q

What is the size of the potential difference that is induced determined by?

A
  • the speed at which the coils or the magnet is moved
  • the number of turns on the coils of the wire
  • the size of the coils
  • the strength of the magnetic field
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6
Q

What are the rules for induction?

A
  • reversing the direction of the poles reverses the induced p.d and current
  • magnetic field produced in the coil always opposes the magnetic field that induces the potential difference
  • moving the coils or the magnet faster induces a greater p.d and current
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7
Q

What is the direction of the potential difference determined by?

A

The orientation of the poles

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8
Q

Why will the number of turns of the coil of a wire increase the induced potential difference?

A
  • each coil will cut through the magnetic field lines
  • total potential difference induced = result of all the coils cutting the magnetic field lines
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9
Q

Why will increasing the area of the coils increase the potential difference?

A

More wire to cut through the magnetic field lines

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10
Q

If a magnet is pushed north first into a coil of wire, the end of the coil closest to the magnet will also become the north pole. Explain why.

A
  • due to the generator effect, a potential difference will induced in the coil
  • induced potential difference always opposes the charge that produces
  • coil will apply a force to oppose the magnet being pushed into i
  • therefore, closest end will become a north pole
  • which repels the magnet
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11
Q

What can the generator effect be used to generate?

A
  • a.c. in an alternator
  • d.c. in a dynamo
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12
Q

What is a simple alternator?

A

A type of generator that converts mechanical energy to electrical energy in the form of an alternating curent

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13
Q

What does a meter pointer show in an alternator?

A

It swings from side to side to show the alternating potential difference

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14
Q

Describe what happens in an alternator?

A

Every half turn, the current will switch direction, as the wire will be in the opposite direction compared to its starting position

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15
Q

What is a dynamo?

A
  • same as an alternator, but at the end, there is a commutator
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16
Q

What is the role of a commutator in a dynamo?

A

The split ring commutator changes the connections between the coil and the brushes every half turn in order to keep the current leaving the dynamo in the same direction
This happens each time the coil is perpendicular to the magnetic field lines

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17
Q

How does a microphone use the principles of electromagnetic induction?

A

They convert the pressure variation in the sound waves into variation in current in electrical circuits

18
Q

Describe how the microphone works

A

1.pressure variations in sound waves cause the diaphragm to vibrate
2. the vibrations of the diaphragm cause vibrations in the coil
3. the coil moves relative to a permanent magnet, so a potential difference is induced in the coil
4. the coil is part of a complete circuit, so the induced potential difference causes a current to flow around the circuit
5. the changing size and direction of the induced current matches the vibrations of the coil
6. the electrical signals generated match the pressure variations in the sound waves

19
Q

Describe how a loudspeaker works

A
  1. Uses a coil which can slide forwards and backwards over the central pole of a circular permanent magnet
  2. Wire from the amplifier moves bakwards and forwards at the same frequency as the changing current
  3. Paper cone then moves the air backwards and forwards which creates the sound
20
Q

What is a transformer?

A

A transformer is an electrical device that can be used to increase or decrease the potential difference of an alternating current

21
Q

How does a transformer work?

A
  1. AC in first coil creates a changing magnetic field
  2. this changing magnetic field cuts through the second secondary coil, inducing an alternating current within it
22
Q

What does a basic transformer consist of?

A
  • primary coil
  • secondary coil
  • iron core
23
Q

Why is an iron core used in a transformer?

A

It is easily magnetised

24
Q

What are the uses of a transformer?

A
  • increase the p.d. of electricity as it is transmitted through the national grid
  • decrease the high voltage electricity as it travels through power lines to the low voltages used in houses
  • in adapters to lower mains voltage used by many electrical devices
25
Q

What is a step up transformer?

A

Increases the voltage and decreases current

26
Q

Describe the coils in a step up transformer

A

coils on primary < coils on secondary

27
Q

What is a step down transformer?

A

Decreases voltage and increases current

28
Q

Describe the coils in a step down transformer

A

coils on primary > coils on secondary

29
Q

What does the output potential difference of a transformer depend on?

A
  • input potential difference
  • number of turns on primary and secondary coils
30
Q

What is the equation used to calculate the output potential difference of a transformer?

A

number of coils on primary/ number of coils on secondary = p.d of primary/ p.d of secondary

31
Q

What is the national grid?

A

Used to transfer electricity across the country

32
Q

Why are high voltages initially used in the national grid?

A
  • A high current produces a high heating effect
  • P = IV, and since power is constant, to decrease th current, we need to increase the pd.
  • therefore, by using high voltages, we improve the efficiency of the transfer
33
Q

Why are the high voltages lowered as they get closer to domestic areas?

A
  • high voltages are dangerous
  • so they lower the voltage as it travels to domestic areas, making it safer to use
34
Q

Describe the journey of electricity from the power stations to factories

A
  1. Power stations
  2. Step-up transformers increase the voltage to 400,00 voltages
  3. electricity sent through transmission lines
  4. step-down transformers reduce voltage to 33,000 volts
  5. Electricity is then delivered to factories
35
Q

Describe the journey of electricity from the power stations to your house

A
  1. Power stations
  2. Step-up transformers increase the voltage to 400,00 voltages
  3. electricity sent through transmission lines
  4. step-down transformers reduce voltage to 33,000 volts
  5. transformers at local substations reduce voltage to 230V from homes, shops and offices
  6. Electricity delivered to your homes
36
Q

State the ideal transfomer equation

A

Vp X Ip = Vs X Is
where p = primary coil
and s= secondary coil

37
Q

What is the voltage produced in power stations?

A

25kV

38
Q

What is the voltage used in transmission lines?

A

400 kV

39
Q

What is the voltage used by small factories?

A

11kV

40
Q

What is the voltage used by large factories?

A

33kV

41
Q

What is the voltage used in homes, shops and schools?

A

230 V

GCSE Edexcel Separate Physics (18 decks)

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