In what way must the voltmeter be connected to the circuit when measuring voltage?

The voltmeter must be connected in a parallel connection to the circuit when measuring voltage. This is essential because a voltmeter is designed to measure the potential difference across two points in a circuit. By connecting it in parallel, it allows the voltmeter to capture the voltage drop across the load or component of interest without significantly affecting the overall circuit operation.

If the voltmeter were to be connected in series, it would interrupt the current flow, leading to an incorrect reading since voltmeters are designed to have a high internal resistance. A series connection does not allow for the measurement of voltage differences effectively. An open connection would imply that there is no contact in the circuit, meaning no measurement could be taken. Similarly, a short connection would create a path of very low resistance, which could potentially damage the voltmeter and lead to erroneous readings. Thus, the parallel configuration is the proper and standard method for accurately measuring voltage in a circuit.