Question:

The ratio of the turns per unit length in two inductors is \[ 2:1. \] Then the ratio of the impedances produced by the inductors is

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For a solenoid, \[ L=\mu_0 n^2Al. \] Therefore, \[ L\propto n^2 \] and at a fixed frequency, \[ X_L=\omega L\propto n^2. \] If turns per unit length double, inductive reactance becomes four times.
Updated On: Jul 29, 2026
  • \(2\)
  • \(4\)
  • \[ \frac{1}{2} \]
  • \[ \frac{1}{4} \]
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The Correct Option is B

Solution and Explanation

Concept: The inductive reactance (impedance due to an inductor) is \[ X_L=\omega L. \] For a long solenoid, \[ L=\mu_0 n^2Al, \] where \[ n=\text{number of turns per unit length}. \] Hence, \[ L\propto n^2. \] Since \[ X_L=\omega L, \] for the same frequency, \[ X_L\propto n^2. \]

Step 1: Write the given ratio. \[ n_1:n_2=2:1. \]

Step 2: Find the ratio of inductances. \[ L_1:L_2 = n_1^2:n_2^2. \] \[ = 2^2:1^2. \] \[ = 4:1. \]

Step 3: Find the ratio of impedances. Since \[ X_L\propto L, \] \[ X_{L1}:X_{L2} = 4:1. \] Therefore, \[ \boxed{\frac{X_{L1}}{X_{L2}}=4} \] \[ \boxed{\text{Answer = (B)}} \]
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