Primary Current in Transformer – Rankers Physics
Topic: Electromagnetic Induction
Subtopic: Transformers

Primary Current in Transformer

A step down transformer connected to an ac mains supply of \(220\text{ V}\) is made to operate at \(11\text{ V}\), \(44\text{ W}\) lamp. Ignoring power losses in the transformer, what is the current in the primary circuit?
4 A
0.2 A
0.4 A
2 A

Solution:

Assuming zero power losses, the input power in the primary circuit equals the output power in the secondary circuit: \(P_{\text{in}} = P_{\text{out}} = 44\text{ W}\). Since \(P_{\text{in}} = V_p I_p\), we get \(I_p = \frac{P_{\text{in}}}{V_p} = \frac{44}{220} = 0.2\text{ A}\).

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