Question

a. A transformer is used to change the 230 volt mains electricity supply to the 12 volts

needed to operate a low voltage halogen lamp. The current through the halogen lamp

is 4 amps. Assuming that the transformer is 100 % efficient determine the:

i. current drawn by the transformer from the mains electricity supply.

Answer 1

The power on both sides is the same:

$$I_1V_1=I_2V_2,\\ I_1=\frac{I_2V_2}{V_1}=4·12/230=0.21\text{ A}.$$