Potentiometer measures the potential difference more accurately than a voltmeter, because:

Introduction:
A potentiometer is an instrument used to measure the potential difference (voltage) accurately in an electrical circuit. It works on the principle of a variable resistor and is designed to draw minimal current from the external circuit. This allows for more accurate voltage measurements compared to a voltmeter.

Explanation:

1. Potentiometer does not draw current from the external circuit:
- A potentiometer is a passive device and does not draw any current from the external circuit.
- It is designed to have a very high input impedance, meaning it does not create any significant load on the circuit being measured.
- This ensures that the potential difference across the potentiometer remains precisely the same as the potential difference across the measured component or circuit.

2. Voltmeter draws current from the external circuit:
- A voltmeter, on the other hand, is an active device that requires current flow through it to measure voltage.
- When a voltmeter is connected in parallel across a circuit, it creates a parallel path for current to flow.
- This additional current drawn by the voltmeter affects the potential difference across the measured component or circuit, leading to a potential error in the voltage measurement.

3. Potentiometer wire has low resistance:
- The wire used in a potentiometer has a low resistance compared to the component or circuit being measured.
- This ensures that the voltage drop across the potentiometer wire is negligible, minimizing any potential error in the voltage measurement.

4. Potentiometer wire has high length and uniform resistance:
- The potentiometer wire is usually long and has a uniform resistance per unit length.
- This allows for precise and accurate measurements of the potential difference along the wire by sliding the contact (jockey) across the wire.
- By adjusting the position of the jockey, the potential difference can be measured at any desired point along the wire, providing accurate voltage readings.

Conclusion:
In conclusion, a potentiometer measures the potential difference more accurately than a voltmeter because it does not draw current from the external circuit, has a wire of low resistance, and allows for precise measurements along its length. This makes it an ideal instrument for accurately measuring voltage in electrical circuits.