transformers

• a transformer consists of:

  • primary coil
  • secondary coil
  • iron core
• an iron core is used as:

  • EASILY MAGNETISED
  • INCREASES STRENGTH OF MAGNETIC FIELD
• the primary coil is connected to an ALTERNATING CURRENT

  this creates a CHANGING MAGNETIC FIELD along the iron core

  when passing to the secondary coil, it INDUCES a POTENTIAL DIFFERENCE
• why won't transformers work with DC?

  produces a constant magnetic field,

  a changing magnetic field is needed to induce a pd
• if the P and S coil have SAME number of turns --> PD same (100% efficient)
• P turns < S turns = PD induced in P coil < PD induced in S coil

  = STEP-UP transformer
• P turns > S turns = PD induced in P coil > PD induced in S coil

  STEP-DOWN transformer
• if primary coil has more turns = step down transformer

  if secondary coil has more turns = step up transformer
• equation relating voltage and turns:

  Vp / Vs = Np / Ns
• power must be conserved

  (100% efficient): electrical power input (power of P coil) = electrical power output (power of S coil)
• power equation: Vs x Is = Vp x Ip

  Vs x Is = power output (S coil)

  Vp x Ip = power input (P coil)

  Power is measured in W
• national grid:

  set-up transformer increases the pd (400,000V)

  transmitted through high voltage cables

  this reduces power loss to surroundings as heat

  step-down transformer decreases the pd (230V)
• transformers reduce power wastage in the national grid