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Why do voltmeters have high input impedance?

  1. It allows for faster measurements

  2. It decreases the loading on circuits being measured

  3. It increases the battery life of the device

  4. It enables measurement of high current

The correct answer is: It decreases the loading on circuits being measured

Voltmeters are designed with high input impedance primarily to reduce the loading effect on the circuits being measured. When a voltmeter is connected across a voltage source, if it has low input impedance, it draws significant current from that source, which can alter the voltage level being measured. This alteration can lead to inaccurate readings because the voltage under measurement might decrease due to the voltmeter's own influence. By having a high input impedance, the voltmeter minimizes the amount of current it draws, effectively ensuring that the circuit under test remains unchanged. This characteristic allows for more accurate and reliable voltage measurements, as it prevents the voltmeter from interfering with the circuit's normal operation. Other options, such as enabling faster measurements, increasing battery life, or allowing for the measurement of high current, do not accurately capture the primary function and purpose of high input impedance in voltmeters.