In this article, we will explore an electrical measuring instrument called a voltmeter, which is used to measure voltage or potential difference between two points or across an electric circuit element in an electric circuit.

What is a Voltmeter?

A voltmeter is an electrical measuring instrument used to determine the voltage or potential difference between two points in an electric circuit. Since it is used to measure voltage and hence its name. Voltmeter is also termed as a voltage meter.

The symbolic representation of a voltmeter is depicted in the following figure.

It is represented by a letter “V” placed inside a circle having two lines representing its terminals.

A voltmeter typically measures the voltage in volts; however, voltmeters are available for measuring a wide range of voltages, from a few millivolts to several kilovolts.

Internal Resistance of Voltmeter

A voltmeter is mainly designed to measure the voltage or potential difference between the two points in an electric circuit. Therefore, it is designed to have a very high internal resistance, so that it does not affect the circuit current when connected to the circuit.

Therefore, a voltmeter always has a very high internal resistance, and an ideal voltmeter is considered to have infinite internal resistance.

The high internal resistance of the voltmeter prevents the current to flow through it and hence shows accurate voltage readings.

Effect of Low Internal Resistance of Voltmeter:

When a voltmeter has a low internal resistance, then it allows some portion of the total circuit current to flow through. This leads to errors in the voltage measurement and shows an inaccurate voltage reading.

Connection Diagram of Voltmeter

The connection diagram of a voltmeter in an electric circuit to measure the voltage across an element is shown in the following figure.

A voltmeter is always connected in parallel with the circuit element across which the voltage has to be measured. This is because a voltmeter has a very high resistance.

If the voltmeter is connected in series with an electric circuit, the amount of circuit current will reduce due to the voltage drop in the high internal resistance of the voltmeter. This results in an inaccurate reading.

Types of Voltmeters

The category-wise classification of voltmeters is given below.

(1). Types of voltmeters based on their construction:

• Permanent Magnet Moving Coil Voltmeter
• Moving Iron Voltmeter
• Electro Dynamometer Type Voltmeter
• Rectifier Type Voltmeter
• Induction Type Voltmeter
• Electrostatic Voltmeter

(2). Types of voltmeters based on output method:

• Analog Voltmeter
• Digital Voltmeter

(3). Types of voltmeters based on the nature of measured voltage:

• DC Voltmeter
• AC Voltmeter

Applications of Voltmeter

A voltmeter is primarily used for measuring the voltage or potential difference between two points in an electric circuit. Some key applications of the voltmeter are listed below:

• To measure voltage between two points or across an element in an electric circuit.
• To determine the value of stored charge in a device like a battery.
• To test a battery or capacitor.
• To check whether the mains output has power or not.
• A voltmeter can be used to construct a voltmeter with the help of a voltage divider and an unknown resistance.

Hence, this is all about the voltmeter, its connection, and its applications. In conclusion, a voltmeter is a widely used instrument employed in electric circuits to measure a voltage across a circuit element or between two points. It is always connected in parallel across the element whose voltage is to be measured.