Q.What is the resistance of an ideal ammeter?
🔒You're viewing a preview — the full solution, concept, methods & PYQ mapping are locked.
🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Ammeter and Voltmeter in Circuits
Ammeter and Voltmeter in Circuits
An ammeter and a voltmeter both measure electrical quantities, but they are connected in opposite ways — and understanding why comes down to a single principle: a good meter must not disturb the circuit it measures.
Ammeter — measures current, connected in series
Current is the same all along a series path, so to read the current in a branch the ammeter must sit in that branch, in series. For it not to change the current it is reading, an ammeter must have very low resistance (ideally zero). It is built from a sensitive galvanometer with a small shunt (a low resistance in parallel) that diverts most of the current, extending the range while keeping the effective resistance tiny.
Voltmeter — measures potential difference, connected in parallel
Potential difference is measured across a component, so a voltmeter is connected in parallel with it. For it not to draw appreciable current away from the component (which would lower the very voltage it is reading), a voltmeter must have very high resistance (ideally infinite). It is a galvanometer with a large resistance in series.
The symmetry to remember
| Ammeter | Voltmeter | |
|---|---|---|
| Measures | Current | Potential difference |
| Connection | Series | Parallel |
| Ideal resistance | Zero | Infinite |
| Extra element | Shunt (parallel) | High resistance (series) |
Since an ammeter is always inserted in series in the very circuit whose current it is meant to measure, any resistance it added would itself alter that current — so an ideal ammeter must of …
An ammeter is connected in series to measure current, so an ideal one must have zero resistance to avoid altering the current it is meant to measure.
An ammeter is always inserted in series in the circuit whose current is to be measured. If it had any resistance, its insertion would itself change the total circuit resistance and hence change the very current being measured. To measure the true, undisturbed current, an ideal ammeter must off …
- CBSE 2026Set ANNUAL1 markQ.What is the resistance of an ideal ammeter?
›Reveal solutionSolution
An ammeter is connected in series to measure current, so an ideal one must have zero resistance to avoid altering the current it is meant to measure.
An ammeter is always inserted in series in the circuit whose current is to be measured. If it had any resistance, its insertion would itself change the total circuit resistance and hence change the very current being measured. To measure the true, undisturbed current, an ideal ammeter must off …
- CBSE 2024Set A1 markQ.Write the name of instrument that measures current in an electric circuit.
›Reveal solutionSolution
Current is measured with an ammeter, connected in series.
The instrument used to measure the electric current flowing through a circuit is called an ammeter. It is always connected in series with the part of the circuit whose current is to be measured, and an ideal ammeter has zero (very low) resistance so that it does not alter the current it is measuring. (A galvanometer …
- CBSE 2022Set I1 markMCQQ.Resistance of ideal ammeter is (A) infinity (B) zero (C) 100 ohm (D) 50 ohm
›Reveal solutionSolution
Ideal ammeter resistance = zero.
An ammeter is connected in series in a circuit to measure current. For the reading to equal the true current, the ammeter must not add any extra resistance in the branch.
…
- CBSE 2022Set HE2171 markQ.Fill in the blank: The voltmeter is always connected in ______ in an electric circuit.
›Reveal solutionSolution
A voltmeter is connected in parallel across the component being measured (and has a very high resistance, so it draws negligible current).
A voltmeter measures the potential difference between two points, so it must be connected across (in parallel with) that part of the circuit, sharing the same two terminals as the component. It is designed with a very high resistance so that connecting it in parallel draws only a negligible current and does not appreciably …
- CBSE 2022Set HE2171 markQ.Match the following. Column A item: 'Ammeter'. Choose its matching entry from Column B:(a) (1 - D/f)(b) Hertz(c) Electromagnetic induction(d) (-v0/u0)(1 + D/fe)(e) V.I.(f) Hershel(g) Instrument of measuring current(h) Instrument of measuring potential(i) Polarisation of light(j) Unit of energy
›Reveal solutionSolution
An ammeter is the instrument used to measure electric current, matching option (g).
An ammeter is a low-resistance instrument connected in series in a circuit to measure the current flowing through that branch, directly match …
- CBSE 2019Set ANNUAL1 markMCQQ.If an ammeter is to be used in place of a voltmeter, then you must connect with the ammeter of a(a) low resistance in parallel(b) high resistance in parallel(c) high resistance in series(d) low resistance in series.
›Reveal solutionSolution
To make an ammeter behave like a voltmeter, a high resistance must be added in series with it.
An ammeter is designed to have a very low resistance so that when inserted in series in a circuit it produces a negligible voltage drop and does not appreciably change the current being measured.
A voltmeter, by contrast, is connected in parallel across the component whose potential difference is to be measured, and must draw as little current as possible from the circuit — which requires it to have a very high resistance.
…
- CBSE 2018Set ANNUAL1 markMCQQ.The resistance of an ideal ammeter should be :(a) very high(b) very low(c) zero(d) infinite
›Reveal solutionSolution
An ammeter is in series with the circuit; to avoid changing the current it must have very low (ideally zero) resistance.
An ammeter measures the current in a branch and is always connected in series with that branch. Whatever resistance the ammeter adds becomes part of the circuit and would reduce the current, giving a wrong reading.
…
🎓Unlock everything free for 14 days
- ✓Full step-by-step solutions
- ✓Concept-first explanations
- ✓Methods, shortcuts & mistakes
- ✓PYQ mapping + timed mock tests
Full access for 14 days. No credit card required.