JEE Main 2015 Physics question

The AC voltage across a resistance can be measured using a:

(1)Moving magnet galvanometer
(2)Moving coil galvanometer
(3)Hot wire voltmeterCorrect
(4)Potentiometer

Answer: (3)

Solution

A hot-wire instrument works by the heating effect of the current, . Since is positive whichever way the current flows, the deflection does not average to zero over an AC cycle; instead the instrument responds to the *rms* value, which is exactly what is wanted — option (3). A moving-coil (or

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Question ID VK-115335