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JEE Main 2019 (11 Jan, Shift 1) · Mutual Inductance

Mutual Inductance question from JEE Main 2019 (11 Jan, Shift 1)

Q56JEE Main 2019 · 11 JAN · SHIFT 1Medium

Mutual Inductance

There are two long co-axial solenoids of same length ll. The inner and outer coils have radii r1 and r2 and number of turns per unit length n1 and n2, respectively. The ratio of mutual inductance to the self - inductance of the inner-coil is:

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Answer: (b)

  1. Mutual inductance: field of outer coil μ0n2I\mu_0 n_2 I links the inner coil, so M=μ0n1n2πr12lM = \mu_0 n_1 n_2 \pi r_1^2 l.
  2. Self-inductance of inner coil: L1=μ0n12πr12lL_1 = \mu_0 n_1^2 \pi r_1^2 l
  3. ML1=n2n1\frac{M}{L_1} = \frac{n_2}{n_1}
  4. So the answer is (b) n2n1\frac{n_2}{n_1}.
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