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The resistances of an ideal current meter (ammeter) and an ideal voltmeter are _____ and _____ respectively.

Asked in GUJCET 2016 · Ammeters and voltmeters in circuits

• (1) ∞, 0
• (2) 0, ∞
• (3) 0, 0
• (4) ∞, ∞

Step-by-step solution

Why the other options are wrong

• (1) This swaps the two. An ammeter of infinite resistance in series would stop the very current it is meant to measure, and a zero-resistance voltmeter in parallel would short-circuit the element.
• (3) A zero-resistance voltmeter placed in parallel would short out the element and read zero. The voltmeter must draw no current, so its resistance must be infinite.
• (4) An ammeter goes in series; infinite resistance would cut the circuit current to zero. The ideal ammeter has zero resistance.

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