When using voltmeters to measure voltage, how must they be connected with a circuit?

When measuring voltage in a circuit with a voltmeter, it is essential to connect the voltmeter in parallel with the component or section of the circuit where the voltage is to be measured. This configuration allows the voltmeter to measure the potential difference across that component while having a much higher internal resistance compared to the circuit elements. This characteristic of the voltmeter minimizes the effect that measuring it has on the overall circuit, ensuring that the measurement reflects the true voltage without significantly altering the performance of the circuit itself.

Connecting the voltmeter in series, around the load, or to the common ground would not yield accurate voltage measurements. In series, the voltmeter would introduce its resistance into the circuit, which would affect the circuit operation and lead to incorrect voltage readings. Similarly, connecting it around the load can create a short circuit, and connecting it only to the common ground does not provide a meaningful voltage measurement since it lacks the reference to the other point in the circuit where the voltage is being assessed. Therefore, the parallel connection is the correct and standard approach for voltage measurement in circuits.