Thursday, December 9, 2021

Alternating Current and Voltmeter

The number of charges flowing in a circuit in a second is called electric current. The electric current is measured using an ammeter. The ammeter is always connected in series in an electric circuit. The potential difference between any two points in a circuit is called the voltage. Voltage is measured using a voltmeter. The voltmeter is connected in parallel in an electric circuit. 

Alternating Current

The flow of electric current consistently in a single direction is called direct current. Battery is an example of direct current flow. Alternating current is when the flow of electrons switches back and forth at regular intervals. The current flowing in normal power lines is alternating current. The advantage of alternating current is that it is cheaper to alter the voltage. The loss of energy while carrying the current over a large distance is lesser in the case of alternating current when compared to direct current.

Alternating current can be produced by different methods. One of the basic methods to create alternating current is by using a single coil AC generator. It consists of two-pole magnets and a single loop of wire having a rectangular shape. AC generators follow Faraday’s principle of electromagnetic induction. The mechanical energy gets converted to electrical energy in a generator. 

Alternating Current Waveform

The time interval between the definite values of two successive cycles is called the time period of the alternating current. The number of cycles in a second is called frequency. The maximum displacement in both directions is called the amplitude of the wave. 


Voltmeters work on the principle of torque. The torque created deflects the pointer of the voltmeter. The deflection of the pointer is directly proportional to the potential difference between the two points. Voltmeters have a very high internal resistance. Voltmeters do not change the current in the circuit. 

Why are Voltmeters connected in Parallel?

The voltmeter is connected such that the internal resistance always remains high. If the voltmeter is connected in series, it reduces the current that flows because of the measured voltage. This alters the reading on the voltmeter. The voltmeter has to be connected in parallel so that the same voltage drop occurs across the voltmeter.

Types of Voltmeters

Voltmeters are classified based on output, construction and measurement. Based on the output, a voltmeter can be classified as an analog voltmeter or digital voltmeter. A voltmeter is classified as DC voltmeter and AC voltmeter based on measurement. On the basis of construction, they are classified as rectifier type voltmeter, MI voltmeter, electrodynamic voltmeter, induction type voltmeter and PMMC voltmeter. 

Voltmeters that display the reading in the numeric form are called digital voltmeters. An analog voltmeter displays readings through a pointer that is fixed on a calibrated scale. AC voltmeter is used in measuring AC voltage in an AC circuit whereas a DC voltmeter measures DC voltage. 

The PMCC uses DC measurement. The MI instrument is used to measure both AC and DC circuits. The rectifier instrument converts the AC quantity into DC quantity with the help of the rectifier.

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