A transformer consists of a primary and secondary coil, wound on a soft iron core.
An alternating current in the primay coil produces an alternating magnetic field in the soft iron core and therefore the secondary coil. This induces an alternating p.d. across the ends of the secondary coil.
In a step-up transformer the p.d. is greater in the secondary coil than the primary coil, and subsequently this is the opposite in a step-down transformer.
The p.d. across the primary and secondary coils of a transformer A and B are related to the number of turns on the coil a and b by:
A/B=a/b
If transformers are assumed to be 100% efficient, the power output would equal the power input.
V X I=v x i (upper case=primary coil,lower case=secondary coil)
Switch mode transformers are ones that operate at a higher frequency, are lighter and smaller, and use very little power when switched on but no load is applied.
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