Verified Solution • 2025–26 Session moderate

QPages 218-219: Q7: HC Verma: Concepts of Physics - Volume 2 Thermal and Chemical Effects of Electric Current Pages 218-219: Q7 Solution: A servo voltage stabiliser restricts the voltage output to . If …

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often treat the power change as proportional to the voltage change (≈ ±1 % power for ±1 % voltage) instead of using $P=V^{2}/R$, which gives about a 2 % power variation. Compute the bulb’s resistance from its rated values and then apply $P=V^{2}/R$ for the extreme voltages.

A servo voltage stabiliser restricts the voltage output to 220 V±1%220 \text{ V} \pm 1\%. If an electric bulb rated at 220 V, 100 W is connected to it, what will be the minimum and maximum power consumed by it?

Step-by-Step Verified Solution

**Answer:** Minimum power = 98 W, Maximum power = 102 W. **Step-by-Step Explanation:** R=2202/100=484 ΩR = 220^2/100 = 484\ \Omega. Voltage range: 220±2.2220 \pm 2.2 V. Minimum: P=217.82/484=98.01P = 217.8^2/484 = 98.01 W. Maximum: P=222.22/484=102P = 222.2^2/484 = 102 W .

All Questions in this Chapter

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