Question

If a generator of emf 440 V and internal resistance 400 $\Omega$ is connected to an external resistance of 4000 $\Omega$, then the potential difference across the external resistance is:

• A. 220 V
• B. 440 V
• C. 200 V
• D. 400 V

Hint:

For a circuit with internal and external resistance, use $I = \frac{{emf}}{R_{{int}} + R_{{ext}}}$, then find the voltage drop across the external resistance as $V = I \cdot R_{{ext}}$.

Answer 1

The Correct Option is D

Total resistance = $R_{{int}} + R_{{ext}} = 400 + 4000 = 4400$ $\Omega$.
Current $I = \frac{{emf}}{R_{{total}}} = \frac{440}{4400} = 0.1$ A.
Potential difference across external resistance: $V = I \cdot R_{{ext}} = 0.1 \times 4000 = 400$ V.