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JEE Main 2026 (2 Apr, Shift 1) · Magnetic Field of Straight Wires

Magnetic Field of Straight Wires question from JEE Main 2026 (2 Apr, Shift 1)

Q12JEE Main 2026 · 2 APR · SHIFT 1Medium

Magnetic Field of Straight Wires

Two identical long current carrying wires are bent into the shapes shown in the following figures. If the magnitude of magnetic fields at the centres P and Q of a semicircular arc are B1B_1 and B2B_2 respectively, then the ratio B1B2\frac{B_1}{B_2} is ______.

Figure

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Answer: (a)

Peach wire: μ0I/4πrarc: μ0I/4r (all ⊗)
  1. (I) Two semi-infinite wires, each μ0I4πr\frac{\mu_0 I}{4\pi r}, plus semicircle μ0I4r\frac{\mu_0 I}{4r}, all into the page: B1=μ0I4πr(π+2)B_1 = \frac{\mu_0 I}{4\pi r}(\pi + 2).
  2. (II) The vertical wire's line passes through Q, so it gives zero. Top wire μ0I4πr\frac{\mu_0 I}{4\pi r} plus semicircle μ0I4r\frac{\mu_0 I}{4r}: B2=μ0I4πr(π+1)B_2 = \frac{\mu_0 I}{4\pi r}(\pi + 1).
  3. B1B2=2+π1+π\frac{B_1}{B_2} = \frac{2 + \pi}{1 + \pi}
  4. So the answer is (a).
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