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IGCSE Physics > Motors, Generators and Transformers > Flashcards

Motors, Generators and Transformers Flashcards

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1
Q

Describe how transformers work

A
  • the primary cook produced a magnetic field which stays within the iron core. Nearly all of it passes through the secondary coil.
  • due to AC current in the primary coil, the field in the iron core is constantly changing direction
  • this rapidly changing magnetic field is then felt by the secondary coil
  • the changing field induces and alternating potential difference across the secondary cool called electromagnetic induction
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2
Q

What is the motor effect?

A
  • When a wire carrying a current is placed in a magnetic field it experiences a force.
  • this can cause the wire to move
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3
Q

What do like poles do to each other and what to opposite poles do?

A
  • like poles repel each other

- opposite poles attract

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4
Q

Does the iron core carry current?

A
  • no, it only carries magnetic field.
  • the soft iron core is purely transferring the changing magnetic field from the primary coil to the secondary coil.
  • no electricity flows around the iron core
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5
Q

What does reversing the current or magnetic field do to the direction of the force?

A
  • reverses the direction of the force
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6
Q

What happens when a current flows through a wire?

A
  • a magnetic field is created around the wire
  • the field is made up of concentric circles perpendicular to the wire, with the wire in the centre

You can use the Right-Hand Thumb Rule to determine the direction of the magnetic field

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7
Q

What does placing north and south poles of two permanent bar magnets near each other do?

A
  • creates a uniform field between the two magnets.
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8
Q

In a step-up transformer, is the potential difference across the secondary cook greater or less than the p.d. across the primary coil?

And vice versa

A
  • greater

- less

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9
Q

What do the relative number of turns on the two coils determine?

A
  • whether the potential difference induced in the secondary coil is greater or less than the potential difference in the primary
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10
Q

Does the iron core carry current?

A
  • no, it only carries magnetic field.
  • the soft iron core is purely transferring the changing magnetic field from the primary coil to the secondary coil.
  • no electricity flows around the iron core
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11
Q

What will happen if you move he magnet in the opposite direction, or if the polarity of the magnet is reversed?

A

The voltage/current will be reversed too.

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12
Q

What is a magnetic field?

A

A region where magnetic materials experience a force.

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13
Q

Describe how transformers work

A
  • the primary cook produced a magnetic field which stays within the iron core. Nearly all of it passes through the secondary coil.
  • due to AC current in the primary coil, the field in the iron core is constantly changing direction
  • this rapidly changing magnetic field is then felt by the secondary coil
  • the changing field induces and alternating potential difference across the secondary cool called electromagnetic induction
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14
Q

What do magnetic field lines show?

A
  • The size and direction of magnetic fields.

- They always point from north to south

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15
Q

What are switch mode transformers?

A
  • a type of transformer that operate at higher frequencies than traditional transformers
  • usually between 50kHz and 200 kHz
  • they can be made much lighter and smaller than traditional transformers that work from a 50Hz mains supply
  • makes them useful for things like mobile chargers and power supplies such as for laptops
  • use very little power when they are switched on but no load is applied
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16
Q

What does a split-ring commutator do?

A

It swaps the contacts every half turn to keep the motor rotating in the same direction

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17
Q

How do you increase the strength of the magnetic field around a solenoid?

A
  • by adding a magnetically ‘soft’ iron core through the middle of the coil.
  • it magnetises and demagnetises very easily
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18
Q

How does the force change with an increase amount of current passing through the conductor

A
  • the force increases
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19
Q

What is the generator effect?

A

The induction of a potential difference in a wire which is experience a change in magnetic field

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20
Q

What are step-down transformers?

A
  • they step the voltage down

- they have more turns on the primary coil than the secondary coil

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21
Q

What is the transformer equation?

A

Vp/Vs = np/ns

22
Q

Explain Fleming’s right-hand rule

A

The fingers mean the same thing as the left-hand rule for motors, except the second finger means induced voltage or current

23
Q

How can a wire experience the full force of the motor effect?

A
  • the wire has to be at 90° to the magnetic field

- if it runs along the magnetic field, it won’t experience any force at all

24
Q

How do you get alternating current?

A

If you keep the magnet (or the coil) moving backwards and forwards, you produce a voltage that keeps swapping direction

25
Q

What is direct current?

A

Current that only flows in one direction

26
Q

What would happen if you supplied DC to the primary coil?

A
  • you would get nothing out of the secondary. It is not constantly changing so there is no induction.
  • you need a changing field to induce a potential difference.
27
Q

How do generators work to produce AC?

A
  • as you turn the magnetic, the magnetic field through the coil changes. This change in the magnetic field induces a voltage, making current flow in the wire
  • when you’ve turned the magnet through a half turn, the direction of the magnetic field through the coil reverses. This reverse the voltage, so current flows in the opposite direction
  • if you keep turning the magnetic in the same directions, the voltage will keep reversing every half turn and you will get AC
28
Q

What happened when a magnet is brought near a magnetic material?

A
  • that material acts as a magnet
  • this magnetism has been induced by the original magnet
  • the closer the magnet and the magnetic material get, the stronger the induced magnetism will be
29
Q

Describe a DC generator.

A
  • DC Generators rotate a cool in a magnetic field (or a magnet in a coil) similar to a motor
  • as the coil spins, a current is induced in the coil. This current changes every half turn
  • DC Generators have a split-ring commutator, so the contacts swap every half turn, keeping the induced current flowing in the same direction
30
Q

Which four factors affect the size of the induced voltage?

A
  • the strength of the magnet
  • the area of the coil
  • the number of turns on the coil
  • the speed of movement
31
Q

Describe a DC generator.

A
  • DC Generators rotate a cool in a magnetic field (or a magnet in a coil) similar to a motor
  • as the coil spins, a current is induced in the coil. This current changes every half turn
  • DC Generators have a split-ring commutator, so the contacts swap every half turn, keeping the induced current flowing in the same direction
32
Q

Name two transformers and what a basic transformer consists of.

A
  • Step-up transformer and step-down transformer

- they both have two coils, the primary and the secondary, joined with a soft iron core.

33
Q

What is an electromagnet?

A

A magnet whose magnetic field can be turned on and off with an electric current.

34
Q

Describe AC Generators

A
  • Generators rotate a coil in a magnetic field. Construction is similar to a motor
  • As a coil or magnet spins, a current is induced in the coil. This current changes direction every half turn.
  • AC Generators have slip rings and brushes so the contacts don’t swap every half turn
  • Faster revolutions produce not only more peaks but higher overall voltage.
35
Q

What is the electrical power output equation?

A

Vp x Ip = Vs x Is

36
Q

Describe AC Generators

A
  • Generators rotate a coil in a magnetic field. Construction is similar to a motor
  • As a coil or magnet spins, a current is induced in the coil. This current changes direction every half turn.
  • AC Generators have slip rings and brushes so the contacts don’t swap every half turn
  • Faster revolutions produce not only more peaks but higher overall voltage.
37
Q

What are step-down transformers?

A
  • they step the voltage down

- they have more turns on the primary coil than the secondary coil

38
Q

What are step-up transformers?

A
  • they step the voltage up

- they have more turns on the secondary coil than the primary coil

39
Q

What is a could of wire called?

A

A solenoid

40
Q

What are step-up transformers?

A
  • they step the voltage up

- they have more turns on the secondary coil than the primary coil

41
Q

Name two transformers and what a basic transformer consists of.

A
  • Step-up transformer and step-down transformer

- they both have two coils, the primary and the secondary, joined with a soft iron core.

42
Q

How do you create potential difference in a conductor?

A
  • moving a magnet in a coil of wire

- moving a conductor in a magnetic field

43
Q

How can you reverse the direction of a motor?

A
  • by swapping the polarity of the direct current supply

- swapping the magnetic poles over

44
Q

What would happen if you supplied DC to the primary coil?

A
  • you would get nothing out of the secondary. It is not constantly changing so there is no induction.
  • you need a changing field to induce a potential difference.
45
Q

What is a magnetic field inside a solenoid like?

A
  • strong

- uniform

46
Q

Explain Fleming’s right-hand rule

A

The fingers mean the same thing as the left-hand rule for motors, except the second finger means induced voltage or current

47
Q

What do the relative number of turns on the two coils determine?

A
  • whether the potential difference induced in the secondary coil is greater or less than the potential difference in the primary
48
Q

What happens to the magnitude of the force as the magnetic field increases in strength?

A

The force increases

49
Q

What does each finger represent in Fleming’s Left Hand Rule

A
  • First finger: the direction of the field
  • Second finger: the direction of the current
  • Thumb: direction of the force
50
Q

In a step-up transformer, is the potential difference across the secondary cook greater or less than the p.d. across the primary coil?

And vice versa

A
  • greater

- less

IGCSE Physics (8 decks)

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