Case: Read the passage and answer the question.
An electric lamp of resistance \( 20\,\Omega \) and a conductor of resistance \( 4\,\Omega \) are connected to a 6 V battery as shown in the circuit.
Calculate the potential difference across the electric lamp.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 5 V
From the figure, the lamp and the \( 4\,\Omega \) conductor are joined end to end with the battery. So they are in series. The same current flows through both, and the resistances add. The battery and the ammeter are taken as ideal.
The total resistance of the circuit is:
\( \begin{aligned} R &= R_{\mathrm{lamp}}+R_{\mathrm{c}} \\ &= 20\,\Omega+4\,\Omega \\ &= 24\,\Omega \end{aligned} \)
The current in the circuit is:
\( \begin{aligned} I &= \frac{V}{R} \\ &= \frac{6\,\mathrm{V}}{24\,\Omega} \\ &= 0.25\,\mathrm{A} \end{aligned} \)
The potential difference across the lamp is:
\( \begin{aligned} V_{\mathrm{lamp}} &= IR_{\mathrm{lamp}} \\ &= 0.25\,\mathrm{A}\times20\,\Omega \\ &= 5\,\mathrm{V} \end{aligned} \)