The ratio of the number of turns of the primary to the ...

CBSE Class 12 Physics 2025 All Sets Solved Paper

Question : 4 of 16

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The ratio of the number of turns of the primary to the secondary coils in an ideal transformer is 20 :1. If 240 V ac is applied from a source to the primary coil of transformer and a 6.0 Ω resistor is connected across the output terminals, then current drawn by the transformer from the source will be.

4.0 A
3.8 A
0.97 A
0.10 A

Solution:

Using the transformer equation

\;{N_P}/{N_S} = \;{V_P}/{V_S}

Given:

NP : N_S = 20 :1 ,\ V_P =240\ V

V_S = \;{V_P}/{20} = \;{240}/{20} = 12 V

Using Ohm’s Law,

I_S = \;{V_S}/{R} = \;{12V}/{6Ω} = 2A

From the transformer current relation:

I_P = I_S × \;{N_S}/{N_P}

I_P = 2A × \;{1}/{20} = 0.10 A

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