JEE Main · 2019 · 09 Jan 2019 · Shift 2 · Alternating Current

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A power transmission line feeds input power at 2300 V to a step down transformer with its primary windings having 4000 turns. The output power is delivered at 230 V by the transformer. If the current in the primary of the transformer is 5 A and its efficiency is

90%

, the output current would be:

(A)50 A
(B)45 A✓ Correct
(C)35 A
(D)25 A

Answer: (B)

Solution

A transformer conserves power up to its efficiency, so

P_{out} = η P_{in}

, that is

V_{s} i_{s} = η V_{p} i_{p}

. The output current is then

i_{s} = \frac{η V _{p} i _{p}}{V _{s}} = \frac{0.9 \times 2300 \times 5}{230} = 45 A

. Notice the primary turns number is not needed once both voltages are given.

JEE Main · 2019 · 09 Jan 2019 · Shift 2 · Single correct option

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