A 12V, 60W lamp is connected to the secondary of a step down transformer, whose primary is connected to ac mains of 220V. Assuming the transformer to be ideal, what is the current in the primary winding?
0.37 A
0.27 A
2.7 A
3.7 A
The Correct Option is B
Solution and Explanation
\(V_sI_s=V_pI_p\) (ideal transformer)
\(\Rightarrow P_{out}=P_{in}\)
\(60=220\times I_p\)
\(I_p=\frac{60}{220}=0.27A\)
So, the correct answer is option (B): 0.27A
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Concepts Used:
Transformers
Transformer is a device used in power transmission to change the AC voltage without changing the frequency between the circuits. Electrical transformer consists of two coils named as the primary coil and secondary coil which is wounded on a soft iron core. The soft iron core is laminated to minimize eddy currents. Both the coil in the transformer has high mutual inductance.Transformers work on the principle of Faraday’s law of electromagnetic induction and mutual inductions.
A mutual electro-motive force is induced in the transformer from the alternating flux that is set up in the laminated core, due to the coil that is connected to a source of alternating voltage.
Other types of transformers:
- Autotransformers: This kind of transformers contain only one coil wound over a laminated core. In Autotransformers, primary and secondary windings share the same coil.
- Power transformers: They are majorly used in power generation stations as they are suitable for major higher voltages.