TRANSFORMERS

TRANSFORMERS

1. EM Induction

   • If a conductor (i.e. a wire) cuts through a MF, a pd is induced across the ends of the conductor. If the conductor is part of a complete circuit, an electric current will flow in the circuit
     • Induction can only happen if: a conductor can be moved in a magnetic field or if a magnet can be moved in a coil of wire
     • Induction does not happen if the conductor moves in the same direction as the magnetic field.
   • The PD can be increased by:
     • Moving magnet/wire faster
     • Stronger magnet
     • Increase number of turns on the coil
     • Increase the area of the coil

2. Switch Mode Transformer

   • E.g. Laptop and mobile phone chargers
   • Smaller PD than the 230 V from the mains electricity.
     • step-down transformer
     • Achieved this by using complex electronic circuits
       • Rapidly switch the current on/off, allowing the a.c. to be changed to a higher frequency.
         • Between 50 Hz and 200 Hz
   • SMT frequencies are between 50-200Hz - a ICT is at 50Hz
   • SMT are relatively small whereas a ICT is heavy due to the iron core.
   • SMT uses very little power whereas ICT uses the same as if a load was applied.

3. A transformer changes the PD. It only works with a.c. electricity. A step-down transformer reduces the PD whereas a step-up transformer increases the PD

   • SUT (2nd more turns) SDT (2nd less turns)

4. An a.c. passes through the primary coil. The a.c. produces a MF that continuously changes direction. The soft iron core increases the strength of the MF. The secondary coil cuts through the changing MF, inducing an alternating PD across the ends of the coil. An a.c flows if a circuit is connected to the secondary coil.

5. V = PD, N = number of turns, I = current

   • Power = PD x Current P = V x A
     • If 100% efficient, the power output from the secondary coil will be the same as the power input to the primary coil.
       • Vp × Ip = Vs × Is
   • Vp × Ip = Vs × Is

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