Verified Solution • 2025–26 Session moderate

QPages 330-331: Q1: HC Verma: Concepts of Physics - Volume 2 Alternating Current Pages 330-331: Q1 Solution: Find the time required for a 50 Hz alternating current to…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students frequently confuse the phase angle for the RMS value ($\pi/4$) with the peak value ($\pi/2$) or the zero crossing ($0$). Remember that $I_{rms} = I_0/\sqrt{2}$, so the sine argument must satisfy $\sin(\omega t) = 1/\sqrt{2}$, which corresponds to $\omega t = \pi/4$, not $\pi/2$.

Find the time required for a 50 Hz alternating current to change its value from zero to the rms value.

Step-by-Step Verified Solution

**Answer:** t=2.5×10−3 st = 2.5 \times 10^{-3} \, \text{s}. **Step-by-Step Explanation:** For a 50 Hz AC, the time period is T=1/50=0.02 sT = 1/50 = 0.02 \, \text{s}. The current starts from zero and reaches its rms value when the phase is ωt=π/4\omega t = \pi/4. Thus, t=T8=0.028=0.0025 st = \frac{T}{8} = \frac{0.02}{8} = 0.0025 \, \text{s} [citation:6].

All Questions in this Chapter

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