The sensitivity of a voltmeter is defined as the reciprocal of its full-scale current and is expressed in ohms per volt (Ω/V). A voltmeter of, say, 20,000 Ω/V presents an input resistance equal to that figure multiplied by the range in use — so on a 10 V range it offers 200 kΩ of input resistance. In other words, a high-sensitivity voltmeter is one that needs only a very small current to produce full-scale deflection, which is exactly what gives it a very high input resistance (impedance).

When a real voltmeter is placed across two points in a circuit, it is effectively connected in parallel with the resistance across which the voltage is being measured. This parallel path draws some current and slightly reduces the effective resistance seen at those points — a disturbance known as the loading effect. The higher the meter's input resistance relative to the circuit resistance, the smaller this diverted current, and the closer the reading is to the true (undisturbed) voltage.

• Why the correct choice is right: Drawing very small current means the meter barely disturbs the network, so the loading effect is minimized and the indicated voltage stays close to the true open-circuit value. This is the direct benefit of high sensitivity.
• Increasing the operating frequency of the circuit is not something a voltmeter does at all — a meter measures voltage and does not set or raise a circuit's frequency.
• Reducing the response time relates to the instrument's dynamics and damping, not to its input resistance; sensitivity does not govern how fast the pointer settles.
• A high-sensitivity meter draws less power from the circuit, not more, so any claim that it increases power consumption of the measuring circuit is the opposite of the truth.

Thus a high-sensitivity voltmeter is preferred because its very high input resistance keeps the current it draws negligible, preserving measurement accuracy.