Verified Solution • 2025–26 Session moderate

QPages 328-329: Q12: HC Verma: Concepts of Physics - Volume 2 Alternating Current Pages 328-329: Q12 Solution: Can you have an AC series circuit in which there is a phase…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students frequently assume the phase angle between source emf and current in a series R‑L‑C circuit can take any value, even 180° or 120°, by “tuning” reactances. In reality φ satisfies τφ = (X_L - X_C)/R with R>0, so φ is confined to -90°<φ<+90°; only a pure reactance (R=0) yields ±90°, never larger angles.

Can you have an AC series circuit in which there is a phase difference of a) 180� b) 120� between the emf and the current?

Step-by-Step Verified Solution

**Answer:** (a) No (b) No. **Step-by-Step Explanation:** The phase difference

\phi

in an AC series circuit satisfies

\tan\phi = \frac{X_L - X_C}{R}

. Since the numerator can range from

-\infty

to

+\infty

while

R > 0

,

\phi

is limited to

-90^\circ < \phi < +90^\circ

. Values like

120^\circ

or

180^\circ

are impossible [citation:14][citation:16].

All Questions in this Chapter

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