Transformers

• AC currents can be increased or decreased by using a transformer.
• Consists of a primary coil, a secondary coil and an iron core.
• The iron core gets magnetized by the incoming current and this magnetism then creates a current in the leaving wire.
• The power is the same on both sides (assume= 100% efficiency).
• For a transformer, you can figure out number of coils and the voltage with: $\frac{Output\ Voltage}{Input\ Voltage}\ =$$\ \frac{Turns\ on\ output\ coil}{Turns\ on\ input\ coil}\ =$$\ \frac{V_p}{V_s}=$$\frac{N_p}{N_s}\$

  or

  $V_{in}\ x\ I_{in}\ =$$\ V_{out}\ x\ I_{out}$
• When magnetic field is changed across the primary coil by connecting it with A.C. an e.m.f. induces across the secondary coil.
• The iron core channels the alternating field through the secondary coil, inducing an alternating e.m.f. across it.
• A step-up transformer increases the voltage and a step-down transformer decreases it.
• Transformers used to make high voltage AC currents.
• Since power lost in a resistor $P\ =$$\ I^2\ x\ R$ , having a lower current will decrease the power loss
• Since transmission cables are many kilometres long they have a lot of resistance, so a transformer is used to increase the voltage and decrease the current to decease power lost.
• The advantages of high-voltage transmission:

  • Less power lost
  • Thinner, light, and cheaper cables can be used since current is reduced