SP13 - Electromagnetic Induction ✓ Flashcards

1
Q

SP13a - Explain how a loop of wire can gain an induced current using a magnet.

A
  • A magnet has a magnetic field around it.
  • Once it moves throughout the wire, the field induces a P.d. in the wire which creates a magnetic field that opposes the direction of the original magnetic field.
  • It also opposes the change that induced the current.
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2
Q

SP13a - How does an alternator work?

A
  • A coil of wire rotates in a magnet field
  • The ends of the coil are connected to slip rings on the axle of the coil, which cause the current to change direction whilst rotating
  • This results in AC supply
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3
Q

SP13a - How does a dynamo work?

A

Same concept as an alternator except:

  • The wires are connected to a split ring commutator
  • The commutator is connected to the carbon brushes
  • Every half-turn the connections are swapped
  • Thus, this produces a direct current
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4
Q

SP13a - How do microphones work?

A
  • (The opposite to loudspeakers)
  • Sound waves cause vibrations in air pressure
  • The pressure causes a diaphragm to move back and forth
  • The diaphragm moves a coil of wire back and forth
  • This causes the coil which is wrapped around a permanent magnet to gain an induced voltage and current
  • The amplitude of the wave affects the volume
  • The frequency affects the pitch
  • Converting sound energy into electrical energy
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5
Q

SP13a - How do loudspeakers work?

A
  • (The opposite to microphones)
  • An a.c. voltage passes througha coil
  • This moves the coil along a permanent magnet
  • The coil hits the diaphram causing it to vibrate
  • This creates soundwaves
  • The higher the current, the larger the frequency and amplitude
  • And so the volume and pitch is higher
  • Converting electrical energy into sound energy
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6
Q

SP13b - What is the national grid?

A

The system that connects power stations to homes to provide electricity nationally

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7
Q

SP13b - What are transformers, both step-up and step-down?

A

Transformers are (not robots in disguise) devices that alter the voltage and current of electricity.

  • SU increase voltage; decrease current
  • SD decrease voltage; increase current
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8
Q

SP13b - Describe the process of transferring energy from power stations to houses and factories.

A
  • Electricity is generated at the power station (11kV)
  • Stepped up (400kV) for transmission lines
  • Stepped down (33kV) Where some is used in large factories
  • Some is stepped down further (11kV) for small factories
  • Rest is stepped down instead (230V) to be used in houses shops etc.
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9
Q

SP13b - Why is electricity stepped up before transmission?

A
  • A higher voltage means a lower current.
  • A higher current would mean a higher power loss (P = I²xR).
  • So the lowest possible current is attained so that the least amount of energy is lost by heating.
  • Low resistance wires are also used (thicker).
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10
Q

SP13b - What is the structure of a transformer?

A

A primary coil (connected to an a.c supply) and a secondary coil with differing amounts of turns, wrapped around an iron core.

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11
Q

SP13b - How do transformers work?

A
  • Changing a.c current supplied
  • This produces a changing magnetic field in primary coil
  • The iron core is induced and carries this changing magnetic field
  • This creates a changing magnetic field in the secondary coil
  • This induces a changing a.c voltage in the wires connected to the secondary coil.
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12
Q

SP13c - What is the voltage current transformer equation and what does it assume?

A

V(p) x I(p) = V(s) x I(s)

[assuming that the transformer is 100% efficient]

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13
Q

SP13b - Which equation links voltage and turns across coils?

A

V(p)/V(s) = T(p)/T(s)

V = Voltage across coil

T = Turns in coil

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14
Q

SP13c - What are the equations for power and energy?

A
  • P = I x V
  • E = P x t , so
  • E = I x t x V
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15
Q

Explain how to produce an electric current by the relative movement of a magnet and a conductor

a) on a small scale in the laboratory
b) in the large-scale generation of electrical energy

A

Small-scale Spinning a coil of wire in between two permanent magnets will cause a current to flow in the wire, which can be shown by a sensitive ammeter (only milliamps will be generated)

Passing a wire through a field will also show a deflection in an ammeter (a reading).

Large-scale In a thermal power station, water heats up and evaporates to form steam

Combustion of fossil fuels / nuclear fission may cause this

The steam is put under pressure and forced into a turbine

This causes the turbine to rotate, which is connected to a massive coil of wire in a strong magnetic field (the generator)

Current is generated in the coil by the spinning motion of the coil through the field.

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