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QPages 328-329: Q14: HC Verma: Concepts of Physics - Volume 2 Alternating Current Pages 328-329: Q14 Solution: Can a hot-wire ammeter be used to measure a direct current of…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often assume hot-wire instruments are exclusively for AC because they measure heating effects, failing to recognize that the root mean square (RMS) of a constant DC current is identical to its instantaneous value. Remember that since the heating effect depends on $I^2$, a steady DC current produces the same thermal response as an AC current of the same RMS magnitude, making the scale universal.

Can a hot-wire ammeter be used to measure a direct current of constant value? Do we have to change the graduations?

Step-by-Step Verified Solution

**Answer:** Yes, it can be used. No, the graduations do not need to be changed. **Step-by-Step Explanation:** A hot-wire ammeter measures the rms value of current based on Joule heating (I2RI^2 R). For a steady DC current, the rms value is equal to the DC value. Therefore, the same graduations are valid [citation:14].

All Questions in this Chapter

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