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SESK: Stuff Everyone Should Know · sesk.info/hamg-voltmeter-impedance

Why do voltmeters have high input impedance?

To decrease loading on the circuit being measured.

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  1. It allows higher voltages to be measured safely
  2. It improves the frequency response
  3. It decreases the loading on circuits being measured ✔

Why: A voltmeter should look like a tiny load so it doesn't change the circuit it is measuring. High input impedance means it draws very little current.

Huh, didn't know that: An oscilloscope is the test instrument that contains horizontal and vertical channel amplifiers.

The dad joke
Why was the voltmeter so polite? It never loaded the circuit with extra demands.
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References

Answer: It decreases the loading on circuits being measured. A voltmeter should look like a tiny load so it doesn't change the circuit it is measuring. High input impedance means it draws very little current.

  1. NCVEC 2023-2027 General Class Pool and Syllabus (6th Errata, Feb 4 2026) ncvec.org/downloads/General%20Class%20Pool%20and%20Syllabus%202023-2027%20Public%20Release%20with%206th%20Errata%20Feb%204%202026.pdf
    It decreases the loading on circuits being measured
    Checked 2026-10-10.

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