Question:

An AC ammeter is used to measure current in a circuit. When a given direct current passes through the circuit, the AC ammeter reads 3 A. When another alternating current passes through the circuit, the AC ammeter reads 4 A. Then the reading of this ammeter, if DC and AC flow through the circuit simultaneously, is

Updated On: Jul 27, 2022
  • 3 A
  • 4 A
  • 7 A
  • 5 A
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The Correct Option is D

Solution and Explanation

Quantity of heat liberated in the ammeter of resistance (i) due to direct current of 3 A =[(3)2R/J)] = [ (3)^2 \, R \, / \, J ) ] (ii) due to alternating current of 4 A =[(4)2R/J)] = [ (4)^2 \, R \, / \, J ) ] \therefore Total heat produced per second = (3)2RJ+(4)2RJ=25RJ \frac{ ( 3)^2 \, R }{ J } + \frac{ ( 4)^2 \, R }{ J } = \frac{ 25 \, R }{ J } Let the equivalent alternating current be I virtual ampere; then I2RJ=25RJ \frac{ I^2 \, R }{ J} = \frac{ 25 \, R }{ J } I = 5 A
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Concepts Used:

Alternating Current

An alternating current can be defined as a current that changes its magnitude and polarity at regular intervals of time. It can also be defined as an electrical current that repeatedly changes or reverses its direction opposite to that of Direct Current or DC which always flows in a single direction as shown below.

Alternating Current Production

Alternating current can be produced or generated by using devices that are known as alternators. However, alternating current can also be produced by different methods where many circuits are used. One of the most common or simple ways of generating AC is by using a basic single coil AC generator which consists of two-pole magnets and a single loop of wire having a rectangular shape.

Application of Alternating Current

AC is the form of current that are mostly used in different appliances. Some of the examples of alternating current include audio signal, radio signal, etc. An alternating current has a wide advantage over DC as AC is able to transmit power over large distances without great loss of energy.