The resistance of an ideal voltmeter is infinite.

Quick Scoop: Ideal Voltmeter 🧪

An ideal voltmeter is a theoretical measuring device used to measure the potential difference (voltage) between two points in a circuit without disturbing the circuit at all.

  • It is always connected in parallel with the component whose voltage you want to measure.
  • To avoid drawing any current from the circuit, it must offer infinite resistance (infinite impedance).

Because current through a branch is I=V/RI=V/RI=V/R, if the voltmeter’s resistance RRR is infinite, the current through it becomes essentially zero, so the rest of the circuit behaves as if the meter is not there.

Why Infinite Resistance Matters

Think of what would happen if a voltmeter had low resistance:

  • A noticeable current would flow through the meter branch.
  • This would change the current distribution in the circuit.
  • The voltage across the component would then change from its original value, so the reading would no longer be accurate.

That’s why textbooks and exam problems consistently state:

The resistance of an ideal voltmeter is infinite.

Real digital voltmeters approximate this by having very high but finite input resistance (often in the megaohm range), which keeps their effect on most circuits very small.

Tiny Exam-Style Summary

  • Question: “What is the resistance of an ideal voltmeter?”
  • Standard answer: Infinite resistance (or “very high, ideally infinite”).

Information gathered from public forums or data available on the internet and portrayed here.