Current Electricity — Easy Practice (Set 2)

Quick Recap — Circuits, Cells & Kirchhoff

• Series: $R = R_1 + R_2 + \ldots$ (same current). Parallel: $\dfrac{1}{R} = \dfrac{1}{R_1} + \dfrac{1}{R_2} + \ldots$ (same voltage).
• Cell: terminal voltage $V = \varepsilon - Ir$; current $I = \dfrac{\varepsilon}{R + r}$.
• Combinations of cells: $n$ in series give emf $n\varepsilon$; $n$ identical in parallel give emf $\varepsilon$ and internal resistance $r/n$.
• Kirchhoff's laws: the junction rule ($\sum I = 0$, charge conservation) and the loop rule ($\sum V = 0$, energy conservation).
• Wheatstone bridge is balanced when $\dfrac{P}{Q} = \dfrac{R}{S}$, so no current flows through the galvanometer.