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MHT CET Medical202623 April 2026Evening ShiftPhysicsMagnetic Effects of CurrentActual

Two wires of same material A and B, having lengths l and 2l 3 carry the currents I and 3I 4 respectively. Both the wires (A and B) are bent into a circles (of single turn). If B_A and B_B are the values of magnetic field at the centres of the respective circles, then the ratio B_B B_A is

Options

  1. A3 4
  2. B2 3
  3. C9 8
  4. D3 8

Correct answer

C. 9 8

Step-by-step solution

The magnetic field at the centre of a circular loop of radius R carrying current I is given by: B = ₀ I 2R Since the wire of length L is bent into a single turn circular loop, the circumference is equal to the length of the wire: 2 R = L R = L 2 Substituting the value of R in the expression for B : B = ₀ I 2 ( L 2 ) = ₀ I L For wire A: L_A = l and I_A = I B_A = ₀ I l For wire B: L_B = 2l 3 and I_B = 3I 4 B_B = ₀ ( 3I 4 ) 2l 3 = 9 ₀ I 8l Taking the ratio of the magnetic fields: B_B B_A = 9 ₀ I 8l ₀ I l = 9 8 Answer:

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