Why must a voltage tester have high resistance?

A voltage tester requires high resistance primarily to prevent excess current flow when measuring voltage. When the tester is connected to a circuit, if the resistance of the tester is low, it could draw a significant amount of current from the circuit being tested. This could lead to inaccurate measurements, potential damage to the tester or the circuit, and can even affect the performance of other components within the circuit.

By maintaining high internal resistance, the voltage tester ensures that it does not alter the circuit conditions significantly. It allows the tester to measure the voltage without drawing excessive current, thus providing an accurate reading that reflects the actual voltage present in the circuit. This is particularly important when testing sensitive electronic devices where even small changes in current can lead to incorrect measurements and potential damage.

Other options, while related to electrical testing, do not directly address this critical aspect of why high resistance is necessary in a voltage tester. For example, indicating plus/minus values pertains more to the display of results rather than the internal characteristics of the tester itself. Similarly, minimizing interference and allowing low voltage input might be important in certain testing scenarios, but they do not highlight the fundamental need for a high-resistance design to avoid loading the circuit.