## Tuesday, 18 February 2014

### Transformer Working Principal - High School Physics Tutorial

Transformer Working Principal

A transformer and its close relative, the Induction coil, use a B field created by a Primary Coil to induce a current in a Secondary coil through induction. The B field changes as the Primary Current changes.

The link between the Primary and Secondary is strengthened by the use of a laminated iron alloy core ( laminated to reduce eddy currents ) to increase the B field. Further, both Primary and Secondary use multiple windings which dictate the strength of the flux between them. More coils, more area hence more flux.

Transformer Working Video:

The Primary is the Input and its windings create a resistance to reduce the primary current when no current is taken from the Secondary.

The mutual link of B field gives a very simple relationship between the applied Primary voltage and the Secondary voltage

Vs / Vp = ns / np

As power is approximately conserved across the transformer,

Pp = Ps , Vp Ip = Vs Is
so
Is / Ip = np / ns

Things are never as simple as the animation implies. The animation has deliberately left out the effect of Lenz's Law on the Primary ( the "back emf") and the changes of phase between Vp and Ip, Vs and Is under different types of load. The assumption is that this transformer is pumping current into a simple resistor in the Secondary stage.