What would be the potential drop across the resistor 300 Ω in the circuit given below?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 60 V
The two resistors carry the same current, so they are in series with the cell. Find the current, then use Ohm’s law for the 300 Ω resistor. The cell is taken as ideal (no internal resistance given).
\( \displaystyle R_{\mathrm{eq}} = 300\,\Omega + 200\,\Omega = 500\,\Omega \)
\( \displaystyle I = \frac{V}{R_{\mathrm{eq}}} = \frac{100\,\mathrm{V}}{500\,\Omega} = 0.2\,\mathrm{A} \)
\( \displaystyle V_{300} = IR = 0.2\,\mathrm{A} \times 300\,\Omega = 60\,\mathrm{V} \)
Shortcut: In series the voltage divides in the ratio of the resistances: \( V_{300} = 100 \times \frac{300}{500} = 60 \) V.