Correct Option
The correct option is Voltmeter.
Explanation
Electric potential difference, often referred to as voltage, is the difference in electric potential between two points in an electric circuit. It represents the work done per unit charge to move a charge between these two points. Measuring this quantity requires an instrument that can be connected across the points of interest without significantly altering the current flowing through the circuit.
Option Analysis
- Voltmeter: Voltmeter (Correct)
A voltmeter is the device used to measure the electric potential difference between two points in a circuit. It is always connected in parallel with the component across which the voltage is to be measured. To ensure accurate measurement and minimal disruption to the circuit, an ideal voltmeter has infinite resistance (practically, very high resistance). - Ammeter: Ammeter (Incorrect)
An ammeter is used to measure the magnitude of electric current flowing through a circuit. It is connected in series with the circuit component. An ideal ammeter has zero resistance to prevent a voltage drop across itself. - Wattmeter: Wattmeter (Incorrect)
A wattmeter is an instrument used to measure the electric power (in watts) of a given circuit. It combines the functions of an ammeter and a voltmeter to measure the rate of energy consumption. - Ohmmeter: Ohmmeter (Incorrect)
An ohmmeter is used to measure electrical resistance. It is typically used when the component is isolated from the power source to determine its opposition to current flow.
Key Takeaway: A voltmeter measures potential difference and is connected in parallel with high resistance, whereas an ammeter measures current and is connected in series with low resistance.