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Difference between Ammeter and Voltmeter
Both Ammeter and Voltmeter are electrical measuring instruments used for measuring the current and voltage in an electrical circuit, respectively. Read through this article to find out more about Ammeter and Voltmeter and how they are different from each other.
Before getting into the differences between Ammeters and Voltmeters, let's get some basic information about these two devices.
What is an Ammeter?
An electrical measuring instrument that is used to measure electric current in an electric circuit is known as ammeter. As the measurement unit of electric current is ampere and this instrument is used to measure the value of current in amperes, hence its name is ammeter.
In order to measure the electric current in an electric circuit, the ammeter is connected in series with the circuit. An ideal ammeter offers zero internal resistance in the circuit. But, a practical ammeter offers a low internal resistance, not zero. The low internal resistance of an ammeter is due to −
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It is connected in series with the circuit, hence total circuit current flows through the device.
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Low voltage drop takes place across the ammeter.
In order to protect the ammeter from heavy currents, the ammeter has an inbuilt fuse. Depending upon the type of current measured, the ammeter can be classified into two types viz. DC ammeter and AC ammeter.
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 Ammeter and Voltmeter
The following table highlights the major differences between Ammeter and Voltmeter −
| Parameter | Ammeter | Voltmeter |
|---|---|---|
| Definition | An electrical measuring instrument which is used to measure electric current in an electric circuit is called ammeter. | The electrical measuring instrument used to measure the voltage between two points in an electric circuit is known as voltmeter. |
| Measured quantity | Ammeter measures electric current. | A voltmeter measures potential difference or voltage. |
| Symbol |  |
 |
| Connection in the circuit | An ammeter is always connected in series with the circuit whose current is to be measured. | A voltmeter is always connected in parallel with the device or circuit whose voltage is to be measured. |
| Internal resistance of ideal device | The internal resistance of an ideal ammeter is zero. | An ideal voltmeter has infinite internal resistance. |
| Internal resistance of practical device | A practical ammeter has very low internal resistance so that it does not affect the flow of electric current through the circuit. | A practical voltmeter has very high resistance so that it restricts the flow of current through it and this allows it to take correct voltage reading. |
| Representation | An ammeter is represented by letter 'A' in a circle. | A voltmeter is represented by a letter 'V' in a circuit. |
| Accuracy | Ammeter is a more accurate device for the electrical and electronic measurement. | The accuracy of a voltmeter is relatively less. |
| Changing of range | In case of ammeter, the changing in its range is not possible. | The range of a voltmeter can be changed. |
| Isolation of circuit | In order to connect an ammeter in a circuit, the circuit must be disconnected from the power supply. | To connect the voltmeter, it is not necessary to disconnect the circuit from the power supply. |
| Obtained from galvanometer | Ammeter is obtained by connecting a shunt resistance of small value in parallel with a galvanometer. | Voltmeter may be obtained by connecting a resistance of high value in series with a galvanometer. |
| Applications | Ammeter is used to measure the value of electric current flowing in a circuit. | In an electric circuit, the voltage or potential difference between two points is measured by using a voltmeter. |
Conclusion
Both Ammeter and Voltmeter are electrical measuring devices. However, the most significant difference between an Ammeter and a Voltmeter is that the ammeter is used to measure the circuit current in an electric circuit, while the voltmeter is used to measure the potential difference or voltage between two points in a circuit.
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