Question

In the circuit shown the readings of ammeter and voltmeter are $4\,A$ and $20\,V$ respectively. The meters are non ideal, then $R$ is :

A. 5$\Omega $
B. > 5$\Omega $
C. < 5$\Omega $
D. 4$\Omega $ to 5$\Omega $

Answer 1

Hint: A resistor is a two-terminal passive electrical component that acts as a circuit element by implementing electrical resistance. Resistors are used in electrical circuits for a variety of purposes, including reducing current flow, adjusting signal speeds, dividing voltages, biassing active components, and terminating transmission lines.

Complete step by step answer:
This dilemma is solved using Ohm's theorem. We assume I=4A since the incoming current is $4\,A$. A voltage drop of $20\,V$ is measured by the voltmeter around the resistor. This means that we can assume $V=IR$ if we use ohm's rule on the resistor. As a result, $20=4R$.This gives us a value of $5$ ohms for $R$. This was the optimal scenario in theory.

For non-ideal metres, the resistance increases as the temperature rises in the physical world.As a result, the correct answer is $B$. Kirchhoff's First Law and Kirchhoff's Junction Rule are two names for Kirchhoff's Current Law. In a circuit, the number of currents in a junction equals the sum of currents outside the junction, according to the Junction law.

The cumulative current entering a junction or a node is equal to the charge exiting the node, according to Kirchhoff's Current Law, so no charge is lost. The voltage around a loop equals the number of all voltage drops in the same loop for every closed network and thus equals zero, according to Kirchhoff's Voltage Law. Since both the ammeter and the voltmeter are not perfect, the voltmeter draws extra current, say $x$. Kirchoff's law states that the current passing through resistance is $4 - x$. Consequently resistance,
$R = \dfrac{{20}}{{(4 - x)}}$
where x > 0 So R > 5

Hence, option B is correct.

Note: An ammeter is a device that measures the current flowing through a circuit.The name comes from the fact that electric currents are measured in amperes. The ammeter is normally wired in series with the circuit that will be used to test the current. A voltmeter is a device that measures the difference in electric potential between two points in an electric circuit. It is connected in a parallel manner. It has a high resistance and therefore draws very little current from the circuit.