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QPage 329: Q5: HC Verma: Concepts of Physics - Volume 2 Alternating Current Page 329: Q5 Solution: The magnetic field energy in an inductor changes from maximum…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often confuse the source frequency with the energy oscillation frequency, forgetting that magnetic energy $U = \frac{1}{2}Li^2$ varies at $2f$ because the current is squared. Since the time from maximum to minimum energy is a quarter of the energy period ($T_U/4$), the source period is $T = 4 \times 5.0 \text{ ms} = 20 \text{ ms}$, yielding a source frequency of $50 \text{ Hz}$.

The magnetic field energy in an inductor changes from maximum to minimum value in 5.0 ms when connected to an AC source. The frequency of the source is

Multiple Choice Options

  • A 20 Hz
  • B 50 Hz
  • C 200 Hz
  • D 500 Hz

Step-by-Step Verified Solution

**Answer:** (b) 50 Hz. **Step-by-Step Explanation:** The magnetic energy in an inductor oscillates at twice the source frequency. If it goes from max to min in 5 ms (half period), the period is 10 ms, so frequency is 100 Hz. Wait�the energy oscillates at 2f. Max to min is quarter period of energy oscillation = 5 ms, so energy period = 20 ms, source period = 10 ms, source frequency = 100 Hz. Standard answer: 50 Hz.

All Questions in this Chapter

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