Transformer Transformer is used to increase or decrease AC Voltage (potential difference). Transformer is consisted of a soft iron core, a primary coil, and a secondary coil. Primary coil is connected to AC supply, while the secondary coil is connected to the electrical component (lamp, computer, TV, etc) Soft iron Primary coil secondary coil Symbol of transformer

Principle of Transformers A transformer works only with alternating current supply (AC supply). Mutual induction: When the primary coil is connected to a source of AC voltage, the changing current creates a changing magnetic field, which is carried through the core to the secondary coil. In the secondary coil the changing field induces a varying voltage. The voltage induced in the secondary coil is called the secondary voltage and voltage induced in the primary coil is called the primary voltage.

In a transformer, the ratio of input voltage to output voltage depends on the ratio of the number of turn on the primary coil and secondary coil, as shown by formula: VS= secondary voltage or output voltage (Volt) VP= primary voltage or input voltage (Volt) NS= number of turns on secondary coil NP= number of turns on primary coil

In the above photograph the school’s transformer was used. 10 In the above photograph the school’s transformer was used. 10.05V (rounded by the meter to 10.1V) across the primary coil of 2,000 turns resulted in an output of 100.5V across the secondary coil of 20,000 turns.

Step-up and step-down transformer Step-up transformer -used to increase the AC voltage (VP < VS ) -secondary voltage is larger than the primary voltage (VP < VS ) -number of turn on secondary coil is larger than on primary coil (NP < NS ) -Output current is smaller than input current (IP > IS ) Step-down transformer -used to decrease the AC voltage (VP > VS ) -secondary voltage is smaller than the primary voltage (VP > VS ) -number of turn on secondary coil is smaller than on primary coil (NP > NS) -Output current is the larger than input current (IP < IS )

In an ideal transformer (100% efficient), the electric power delivered to the secondary coil equals the power supplied to the primary coil. It can be represented by the following equations: PP = PS VP .IP = VS .IS PP = Power in primary coil or power input (Watt) PS = Power in secondary coil or power output (Watt) IP = Current in primary coil or current input (Ampere) IS = Current in secondary coil or current output (Ampere)

Energy Losses in a Transformer are caused by: Resistance of winding The windings of copper wire – have some resistance - heat is produced Eddy Currents. Iron core – changing magnetic field of the primary – induced – current (eddy currents)- caused heating. Reduced by laminating core made of sheets Leakage of field lines Field lines produced – primary may not cut the secondary – has air gap or badly designed

Application of Eddy Currents: Speedometer

Application of Eddy Currents: Metal Detector

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