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Q11.7: NCERT Physics - Part 2 THERMODYNAMICS 11.7 Solution: An electric heater supplies heat to a system at a rate of 100…

⚠️ Common Exam Traps & Conceptual Pitfalls

In the first law, $Delta U = Q - W$, $W$ is the work done by the system. If the system performs work, you must subtract it; adding it would incorrectly inflate the internal‑energy change.

An electric heater supplies heat to a system at a rate of 100 W. If system performs work at a rate of 75 joules per second. At what rate is the internal energy increasing?

Step-by-Step Verified Solution

**Answer:** Rate of increase of internal energy = 25 W **Step-by-Step Explanation:** Using the first law of thermodynamics:
dQdt=dUdt+dWdt\frac{dQ}{dt} = \frac{dU}{dt} + \frac{dW}{dt}
dUdt=dQdt−dWdt=100−75=25 W\frac{dU}{dt} = \frac{dQ}{dt} - \frac{dW}{dt} = 100 - 75 = 25 \text{ W}

All Questions in this Chapter

Q11.1 Q11.2 Q11.3 Q11.4 Q11.5 Q11.6 Q11.7 Q11.8

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