Which instrument is used to measure voltage in a circuit?

The voltmeter is the instrument specifically designed to measure voltage in a circuit. It operates by connecting across the two points in the circuit between which the voltage is to be measured. The voltmeter’s internal resistance is typically very high to minimize the current drawn from the circuit, ensuring that the measurement does not significantly alter the circuit's operation. This high resistance allows for accurate voltage readings without affecting the other components in the circuit.

In contrast, other instruments listed serve different functions. An ampermeter is used for measuring current in a circuit, usually requiring a lower resistance connection. An oscilloscope is a complex device that visually displays voltage changes over time rather than providing a straightforward voltage measurement. An ohmmeter measures resistance in a circuit, which is a different electrical property altogether, not directly assessing voltage. Understanding the specific purpose of each device helps clarify why the voltmeter is the correct choice for measuring voltage.