[Physics Class Notes] on Voltmeter Pdf for Exam

In physics, there are different types of measuring equipment for electrical purposes. For measuring electrical current, voltage, and other parameters, the instruments are different. A voltmeter is one of the measurement equipment for electrical parameters. The voltmeter is used to measure the electrical potential difference between two points of an electrical circuit. To measure the potential difference, the voltmeter is connected in parallel with the electrical circuit. The voltmeter takes a small amount of current to form the power source to function. The amount of that current is too less and it doesn’t affect the circuit current. In this article, we are discussing voltmeter definition, function, unit, and other information.

Voltmeter Function

The voltmeter is a vital instrument used to measure voltage. It is used to measure both direct and alternating electric current. A voltmeter is a current-controlled device, which means it needs a current to function. The voltmeter is connected with the electrical circuit in parallel. A voltmeter has high resistance so that it consumes less current to function. That is why the Current consumption by the voltmeter doesn’t affect the circuit current. In the parallel connection, the high resistance of the voltmeter gives almost the same impedance as the impedance of the load resistance. The voltage in the parallel circuit and the voltage between the voltmeter and the load become the same. Thus, the voltmeter measures the voltage of the electrical circuit. This is the working principle of a voltmeter.

Unit of Voltmeter

The voltmeter is the major instrument to measure the voltage of an electrical circuit. Therefore, the unit of the voltmeter is the unit of the voltage measured in the voltmeter. The units of voltmeter are millivolt, kilovolt and volt. These three are the most used units. 1 volt = 0.001 millivolts and 1 volt = 1,000 Kilovolts.

Classification of Voltmeter

Now, we are going to discuss different types of voltmeters. Voltmeters are classified depending on three factors, which are output, construction, and measurement. Voltmeters are of two types based on output – analog and digital voltmeters. Analog voltmeters display voltage with moving needles. Digital voltmeters show the voltage in a digital display with an accurate value.

Voltmeters are of five types based on construction – rectifier type voltmeter, MI voltmeter, electrodynamic voltmeter, PMMC, induction type voltmeter. Rectifier type voltmeter measures the voltage using a permanent magnet moving coil and rectifying elements. Moving iron (MI) voltmeter measures the voltage using the magnetic field created by moving iron. The electrodynamic voltmeter is constructed with a series connection of the windings, which gives the most accurate voltage values. PMMC voltmeters are constructed using permanent magnets. Induction type voltmeter Functions on the two-pole method or shaded pole method. 

The voltmeters are classified into two types depending on the measurement, which are DC voltmeter and AC voltmeter. A DC voltmeter is used to measure the voltage of a DC power source. AC voltmeter is used to measure the voltage of an AC power source. These are the different types of voltmeters to measure the voltage of an electrical circuit.

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How to Measure Voltage Using a Voltmeter?

To measure the voltage of an electrical circuit, some particular steps should be followed. The essential steps are mentioned below.

• Turn on the dial of the power source. If the circuit voltage is unknown, set the range to the highest value and set the dial on the source voltage.

• Insert the black wire into the COM jack and the red wire into the voltage jack.

• Remove the lead in reverse order, which means first red and then black.

• Connect the test leads (first black and then red) to the circuit.

• Read the voltage in the display. Remove the test leads in reverse order.

All the steps should be completed carefully. Otherwise, the measurement can be wrong or you can be injured.

Solved Examples

1. What is the Main Function of the Voltmeter?

Solution: Voltmeter is converted from a galvanometer. The main function of a voltmeter is to measure the voltage of an electrical circuit.

2. What is the Unit of a Voltmeter?

Solution: the main units of the voltmeter are volt, millivolt, and kilovolt.

3. Why is the Voltmeter Connected in Parallel?

Solution: Voltmeter has high resistance and it consumes less current to function. The current consumed by the voltmeter doesn’t affect the circuit. That is why the voltmeter is connected in parallel with the circuit.

4. What is the Main Difference Between DC and AC Voltmeters?

Solution: DC voltmeter is to measure DC voltage. AC voltmeter measures AC voltage.