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JEE Main 2023 (30 Jan, Shift 2) · Force on Current-Carrying Conductors

Force on Current-Carrying Conductors question from JEE Main 2023 (30 Jan, Shift 2)

Q36JEE Main 2023 · 30 JAN · SHIFT 2Medium

Force on Current-Carrying Conductors

A current carrying rectangular loop PQRS is made of uniform wire. The length PR=QS=5 cmPR = QS = 5\text{ cm} and PQ=RS=100 cmPQ = RS = 100\text{ cm}. If ammeter current reading changes from I to 2I2I, the ratio of magnetic forces per unit length on the wire PQPQ due to wire RSRS in the two cases respectively (fPQI:fPQ2I)\left(f_{PQ}^{I} : f_{PQ}^{2I}\right) is:

Figure

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Answer: (a)

  1. PQ and RS are identical branches in parallel, so each carries half the total current.
  2. Force per unit length f=μ0(I/2)(I/2)2πd∝I2f = \frac{\mu_0 (I/2)(I/2)}{2\pi d} \propto I^2.
  3. fIf2I=I2(2I)2=14\frac{f^{I}}{f^{2I}} = \frac{I^2}{(2I)^2} = \frac{1}{4}
  4. So the answer is (a) 1 : 4.
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