Terminal Voltage And Internal Resistance

Question

While measuring a battery on a test bench, its terminal voltage drops from 12 volts on open circuit to 10.5 volts when delivering 3 amperes, so what is the internal resistance?

RankGuru · Accepted Answer

The open-circuit terminal voltage equals the emf because no current flows, so $\varepsilon = 12$ V, and once current is drawn the terminal voltage falls according to $V = \varepsilon - Ir$, a relationship developed in NCERT Class 12, Chapter 3 (Current Electricity). The voltage lost inside the cell is $\varepsilon - V = 12 - 10.5 = 1.5$ V, and this drop occurs across the internal resistance carrying 3 A. Hence $r = \frac{\varepsilon - V}{I} = \frac{1.5}{3} = 0.5$ ohm. The option 4 ohm mistakenly divides the terminal voltage difference by a smaller misread current figure rather than the actual 3 A. The option 3.5 ohm divides the full 10.5 V by 3 A, wrongly treating the entire loaded terminal voltage as if it appeared across the internal resistance. The option 1.5 ohm reports the internal voltage drop as if it were directly the resistance, forgetting the crucial step of dividing by the current. A magnitude check confirms plausibility: a small internal resistance of 0.5 ohm producing a modest 1.5 V drop at 3 A is typical for a healthy battery, and the units of volts divided by amperes correctly yield ohms, so both the sign and magnitude of the answer are physically reasonable.

Terminal Voltage And Internal Resistance

Select the correct option:

🔒 Solution Hidden from View

More current electricity Practice Questions

Engineers relate the current density inside a conductor to the local electric field through the mate...

Three identical cells, each with internal resistance 0.6 ohm, are connected in parallel to reduce th...

A battery of emf 12 volts and internal resistance 3 ohm drives a variable load resistor, so for what...

An electric heater rated to carry 5 amperes operates across a 220 volt mains supply in a kitchen, so...

Current passes through a 20 ohm resistor at 2 amperes for 5 minutes in a demonstration, so how much ...

Four identical cells, each of emf 1.5 volts and internal resistance 0.2 ohm, are connected in series...

A cell of emf 6 volts and internal resistance 0.5 ohm is connected to an external resistor of 2.5 oh...

Two resistors of 6 ohm and 3 ohm are wired side by side between the same two nodes of a circuit, so ...

At a junction in a network, currents of 5 A and 3 A enter while currents of 4 A and I leave through ...

A potentiometer is often preferred over a voltmeter for measuring the emf of a cell accurately, so w...

In a balanced Wheatstone bridge the galvanometer shows no deflection, so which relation among the fo...

In a meter bridge the balance point is found at 40 cm from one end while the known resistance in the...

About This Question

Solution