SP13 - Electromagnetic Induction ✓ Flashcards Preview

Edexcel GCSE Physics COPY > SP13 - Electromagnetic Induction ✓ > Flashcards

Flashcards in SP13 - Electromagnetic Induction ✓ Deck (14)
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1

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

  • 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 opposite to original change.

2

SP13a - How does an alternator work?

  • A coil of wire wrapped around an iron core is rotated inside a magnetic field
  • Wires from the coil are connected to slip rings on the axle of the coil
  • The slip rings make electrical contact through carbon brushes
  • This produces an alternating current

3

SP13a - How does a dynamo work?

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

4

SP13a - How do microphones work?

  • (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

5

SP13a - How do loudspeakers work?

  • (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

6

SP13b - What is the national grid?

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

7

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

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

8

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

  • 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.

9

SP13b - Why is electricity stepped up before transmission?

  • 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).

10

SP13b - What is the structure of a transformer?

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

11

SP13b - How do transformers work?

  • 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.

12

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

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

[assuming that the transformer is 100% efficient]

13

SP13b - Which equation links voltage and turns across coils?

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

V = Voltage across coil

T = Turns in coil

14

SP13c - What are the equations for power and energy?

  • P = I x V
  • E = P x t  , so
  • E = I x t x V