Verified Solution • 2025–26 Session moderate

QPage 217: Q1: Thermal and Chemical Effects of Electric Current Solutions — HC Verma: Concepts of Physics - Volume 2

⚠️ Common Exam Traps & Conceptual Pitfalls

Students frequently assume the filament’s resistance will keep dropping or that the current will continue falling indefinitely, forgetting that a metal filament has a positive temperature coefficient: as it heats, $R$ rises, reducing $I$, and the process stops when Joule heating equals radiative loss, giving a steady $I$.

If a constant potential difference is applied across a bulb, the current slightly decreases as time passes and then becomes constant. Explain.

Step-by-Step Verified Solution

**Answer:** The current decreases initially because the resistance of the filament increases with temperature, and then becomes constant when the heat produced equals the heat radiated. **Step-by-Step Explanation:** Initially, the filament is at room temperature. When a constant potential difference is applied, the filament heats up due to Joule heating. For metals, resistance increases with temperature. Since i=V/Ri = V/R, as RR increases, the current decreases. After some time, the rate of heat produced by the current equals the rate of heat radiated to the surroundings. The temperature stabilises, and hence the resistance and current become constant .

All Questions in this Chapter

QPage 217: Q1 QPage 217: Q2 QPage 217: Q3 QPage 217: Q4 QPage 217: Q5 QPage 217: Q6 QPage 217: Q7 QPage 217: Q8 QPage 217: Q9 QPage 218: Q1 QPage 218: Q2 QPage 218: Q3 QPage 218: Q4 QPage 218: Q5 QPages 217-218: Q1 QPages 217-218: Q2 QPages 217-218: Q3 QPages 217-218: Q4 QPages 217-218: Q5 QPages 217-218: Q6 QPages 217-218: Q7 QPages 217-218: Q8 QPages 218-219: Q1 QPages 218-219: Q2 QPages 218-219: Q3 QPages 218-219: Q4 QPages 218-219: Q5 QPages 218-219: Q6 QPages 218-219: Q7 QPages 218-219: Q8 QPages 218-219: Q9 QPages 218-219: Q10 QPages 218-219: Q11 QPages 218-219: Q12 QPages 218-219: Q13 QPages 218-219: Q14 QPages 218-219: Q15 QPages 218-219: Q16 QPages 218-219: Q17 QPages 218-219: Q18 QPages 218-219: Q19 QPages 218-219: Q20 QPages 218-219: Q21 QPages 218-219: Q22 QPages 218-219: Q23 QPages 218-219: Q24

Related Learning Resources & Exam Preparation

Chapter Practice Bank
Practice all topic-wise questions from Thermal and Chemical Effects of Electric Current
Reference Textbook Solutions
Explore complete chapter exercises for HC Verma: Concepts of Physics - Volume 2
Competitive PYQ Question Bank
Browse year-wise authentic previous years' questions with solutions
Authentic CBT Mock Tests
Simulate official exam environment with live timer and percentile scoring