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Difference between Potentiometer and Voltmeter
Potentiometer and voltmeter are both types of measuring devices used to measure the voltage. However, one most significant difference between the potentiometer and the voltmeter is that the potentiometer is used for measuring the EMF of a source while the voltmeter is used to measure the potential difference (or voltage) between two points in a circuit.
The other differences between voltmeter and potentiometer are given below in the tabular form. Also, a short description of voltmeter and potentiometer is added for the better understanding of the differences.
What is a Potentiometer?
A potentiometer is a three-terminal measuring instrument used to measure the unknown EMF (or voltage) by comparing it with a known EMF (or voltage). The potentiometer is also known as 'Pot' or 'Potmeter'.
The working principle of the potentiometer is that a potential drop across any part of a wire is directly proportional to the length of the wire, provided that the wire has the uniform area of cross-section and a uniform electric current flows through it. But, many other types of potentiometers are also available.
Basically, a typical potentiometer consists a long wire of uniform cross-section which is cut into several pieces and are placed side by side and again connected at the ends with a thick copper strip. The copper strip converts the parallel wires into a single wire.
The most common application of the potentiometer is that it is used for measuring the EMF and the internal resistance of a given cell.
What is a Voltmeter?
A voltmeter is an electrical measuring instrument that is used to measure the potential difference or voltage across two points in an electric circuit. A voltmeter is also known as voltage meter because it measures value of voltage in an electric circuit.
In order to measure the potential difference or voltage across a device, the voltmeter is connected in parallel to the device. The voltmeter is connected in parallel with the circuit so that the same voltage drop occurs across it.
An ideal voltmeter has infinite internal resistance. Although, the internal resistance of a practical voltmeter is not infinite, but it is very high. The high resistance of the voltmeter is mainly because it is used for the measurement of voltage between two terminals of a circuit, i.e. the high resistance of the voltmeter will restrict the current to flow through it and the whole current will flow through the load and thus the voltmeter takes the correct reading of the voltage across the device.
Based on the method used to display the measurement, the voltmeters are classified into two types viz. analog voltmeter (shows reading by the deflection of pointer) and digital voltmeter (shows the reading on a seven segment digital display).
Difference between Potentiometer and Voltmeter
The major differences between a potentiometer and a voltmeter are highlighted in the following table −
| Parameter | Potentiometer | Voltmeter |
|---|---|---|
| Definition | A potentiometer is a three terminal measuring device used to measure the unknown EMF of a source (such as a cell) by comparing it with a known EMF. | The voltmeter is a two terminal measuring device which is used to determine the potential difference (or voltage) between any two terminals in an electric circuit. |
| Alternate name | Potentiometer is also called 'Pot' or 'Potmeter'. | Voltmeter is also known as voltage-meter. |
| Circuit Symbol |  |  |
| Measuring quantity | Potentiometer measures unknown EMF of a source. | Voltmeter measures voltage between two terminals. |
| Number of terminals | A potentiometer has three terminals. | There are two terminal in a voltmeter. |
| Need of source of known EMF | Potentiometer requires a source whose EMF is known. | There is no need of source of known EMF in case of a voltmeter. |
| Current drawn from source | During the measurement of the unknown EMF, a potentiometer does not draw any current from the driving source of the known EMF. | While measuring the potential difference or voltage, a voltmeter draws some current from the source. |
| Resistance | While measuring the unknown EMF, the resistance of the potentiometer becomes infinite. | During the measurement of the voltage, the resistance of the voltmeter is very high but finite. |
| Accuracy | The accuracy of potentiometer is more. | The voltmeter measures the quantity less accurately. |
| Sensitivity | The sensitivity of a potentiometer is high. | The sensitivity of a voltmeter is low. |
| Type of instrument | A potentiometer uses the null-deflection type instrument. | Voltmeter uses the deflection type instrument. |
| Direct reading | A potentiometer does not give a direct reading, i.e. it gives the reading by comparing with some known value. | A voltmeter gives the direct reading of the voltage. |
| Measurement of internal resistance of source | The internal resistance of a source (cell) can be measured using a potentiometer. | A voltmeter cannot be used to measure the internal resistance of a source. |
| Applications | A potentiometer is used for various purposes such as to measure the EMF of a cell, internal resistance of a cell, thermos-EMF, calibration of ammeter & voltmeter, etc. | A voltmeter can only be used to measure thepotential difference (or voltage) between any two points of a circuit. |
Conclusion
The above table shows several differences between a potentiometer and a voltmeter. However, the most significant difference between the two is that a potentiometer is a three-terminal device used for measuring the unknown EMF of a cell accurately, whereas a voltmeter is a two-terminal instrument used to measure voltage between two points in a circuit.
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