Transformers

Question 1

What are transformers?

Answer 1

• devices that use EM induction to change the size of the voltage for an alternating current

Question 2

How does a transformer work?

Answer 2

• AC current flowing in the primary (or input) coil produces magnetic flux
• the changing magnetic field is passed through the iron core to the secondary (output) coil
  
  • where it induces an alternating voltage of the same freq as the input voltage

Question 3

Using Faraday’s law, how can the induced emf in both the primary and secondary coils be calculated?

Answer 3

• V_p = N_p ΔΦ / Δt
• V_s = N_s ΔΦ / Δt
• therefore
• N_s / N_p = V_s / V_p

Question 4

WHat are step-up and step-down transformers?

Answer 4

• step-up
  
  • increase voltage
  • by having more turns in secondary coil than the primary
• step-down transfers
  
  • reduce voltage
  • have fewer turns on the secondary coil

Question 5

Why does IpVp = IsVs not happen?

Answer 5

• not 100% efficient
• power in does not equal power out
• that is forn an ideal transformer

Question 6

What causes the loss in power from the transformer

Answer 6

• eddy currents in the transform’s iron core
• eddy currents are looping currents induced by the changing magnetic flux in the core
  
  • they crease a magnetic field that acts against the field that induced them , reducing the field strength
  • they also disspate energy by general heat

Question 7

How are eddy currents reduced>?

Answer 7

• laminating the core with layer of insulation

Question 8

How is heat also generated? How is it reduced?

Answer 8

• caused by resistance in the coils
• thick copper wire used , which has a low resistance

Question 9

How are transformers used in the national grid?

Answer 9

• electricity from power station sent round the country in the national grid at the lowest possible currrent
  
  • because the power losses due to the resistance of the cables is equal to P = I²R
  • so if you double the transmitted current, you quadruple the power lost
• since power = IV, low current means a high voltage
• transformers allow us to step up to voltage to aroudn 400,000V for transmission through national grid
• and reduce in to 230V for domestic use