Ncert Exercises & Solutions

A 60 W load is connected to the secondary of a transformer whose primary draws line voltage. If a current of 0.54 A flows in the load, what is the current in the primary coil? Comment on the type of transformer being used.

Hint: The type of transformer depends on the primary voltage and the secondary voltage.

Step 1: Given,

P_{S} = 60 W, I_{S} = 0.54 A

Current in the primary,

I_{P} = ?

Taking line voltage as 220 V.

We can write Since,

\Rightarrow P_{L} = 60 W, I_{L} = 0.54 A

\Rightarrow V_{L} = \frac{60}{0.54} = 110 V . . . . (i)

Step 2: Voltage in the secondary

(E_{s})

is less than the voltage in the primary

(E_{p})

Hence, the transformer is a step-down transformer.

Since the transformation ratio;

r = \frac{V_{S}}{V_{P}} = \frac{I_{P}}{I_{S}}

Substituting the values,

\frac{110 V}{220 V} = \frac{I_{P}}{0.54 A}

On solving;

I_{P} = 0.27 A

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