Final answer:
To measure the potential difference across a light bulb, a voltmeter is connected in parallel with the bulb. The voltmeter's leads should be attached to points on either side of the bulb to read the correct voltage, making sure to start with the largest scale to protect the metre.
Step-by-step explanation:
To measure the potential difference across a light bulb in a circuit, a voltmeter must be connected properly. This involves attaching the voltmeter in parallel to the light bulb. By connecting the voltmeter in parallel, it ensures that the voltmeter will measure the same voltage that the light bulb is experiencing. When using the voltmeter, it's important to first connect to the largest scale available to avoid damaging the meter if the measured voltage exceeds its limits. The leads of the voltmeter should be connected to the points across the light bulb where the potential difference is to be measured.
Keep in mind that a voltmeter is different from an ammeter, which is used to measure current. An ammeter must be placed in series with the circuit elements. For voltmeters, however, the two leads connect to either side of the bulb, without altering the pathway of the current that powers the bulb. The modern digital voltmeters are convenient to use and provide a direct readout of the voltage.