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Question

Two inductors of 8 H and 2 H connected in series opposing with mutual inductance of 1 H will have equivalent:

This question was previously asked in
RRB JE 2025 CBT 2 Mechanical and Allied Engg Question Paper English (2-Jul-2026) (Shift-1)
The correct answer is

8 H

To find the equivalent inductance of two inductors connected in series opposing with mutual inductance, we use the following formula:

L_{\text{eq}} = L_1 + L_2 - 2M

where:

  • L_1 is the inductance of the first inductor (8 H).
  • L_2 is the inductance of the second inductor (2 H).
  • M is the mutual inductance between them (1 H).

Substitute the values into the formula:

L_{\text{eq}} = 8 + 2 - 2 \times 1

Simplify the expression:

L_{\text{eq}} = 8 + 2 - 2 = 8 \, \text{H}

Therefore, the equivalent inductance is 8 H.

Let's verify the options:

  • 8 H - This is the correct answer.
  • 9 H - Incorrect, evaluated value is 8 H.
  • 5 H - Incorrect, does not match the calculation.
  • 11 H - Incorrect, does not match the calculation.

This confirms that the correct answer is 8 H.

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Important Questions from Mutual Inductance

  1. Two inductors whose self-inductance is 80 mH and 60 mH are connected in parallel aiding. The equivalent inductance of the combination is 48.75 mH. Calculate their mutual inductance.

  2. Two inductors L1 = 20 mH and L2 = 40 mH are connected in series so that their equivalent inductance is 50 mH. The mutual inductance between the two coils is _______.

  3. Which statement is INCORRECT for mutual inductance?

  4. Calculate the total inductance (in H) of the circuit shown below:

  5. A transformer has 350 primary turns and 1050 secondary turns. The primary winding is connected across a 230 V, 50 Hz supply. The induced EMF in the secondary will be

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