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JEE Main 2021 (18 Mar, Shift 1) · Ampere's Law, Cylinders, Solenoid & Toroid

Ampere's Law, Cylinders, Solenoid & Toroid question from JEE Main 2021 (18 Mar, Shift 1)

Q46JEE Main 2021 · 18 MAR · SHIFT 1Difficult

Ampere's Law, Cylinders, Solenoid & Toroid

Four identical long solenoids A, B, C and D are connected to each other as shown in the figure. If the magnetic field at the center of A is 3T, the field at the center of C would be: (Assume that the magnetic field is confined with in the volume of respective solenoid).

Figure

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Answer: (d)

  1. Identical solenoids: B=μ0nI∝IB = \mu_0 n I \propto I.
  2. A carries the full current ii; B, C, D are identical and in parallel, so each carries i3\frac{i}{3}.
  3. BC=3 T3=1B_C = \frac{3\text{ T}}{3} = 1 T
  4. So the answer is (d) 1 T.
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