Question:medium

A parallel combination of 'n' cells of emf 'E' and internal resistance each, are connected across the external resistance 'R'. If the external resistance 'R' is negligibly small, then the current 'I' through the external resistance is:

Show Hint

When external resistance is negligible ($R \approx 0$), cells should always be connected in series to get maximum current. Connecting them in parallel as done here means the total current is simply equal to the current from a single cell ($I = \frac{E}{r}$), but because there are $n$ cells in parallel dividing the load, the short-circuit expression scales directly by the branch multiplier!
Updated On: May 20, 2026
  • $I=\frac{nE}{R}$
  • $I=\frac{rE}{n}$
  • $I=\frac{E}{nR}$
  • $I=\frac{E}{R}$
Show Solution

The Correct Option is A

Solution and Explanation

Understanding the Concept: For a parallel combination of $n$ identical cells, each having an electromotive force $E$ and an internal resistance $r$, the equivalent emf ($E_{\text{eq}}$) of the combination remains equal to the emf of a single cell ($E_{\text{eq}} = E$). The equivalent internal resistance ($r_{\text{eq}}$) of the $n$ parallel branches is given by: \[ r_{\text{eq}} = \frac{r}{n} \] When connected across an external resistor $R$, the total current $I$ flowing through the circuit is determined by Ohm's law for a complete circuit: \[ I = \frac{E_{\text{eq}}}{R + r_{\text{eq}}} = \frac{E}{R + \frac{r}{n}} \]
Step 1: Apply the given condition to simplify the current equation.
The problem states that the external resistance $R$ is negligibly small compared to the internal resistance components ($R \approx 0$). Substituting $R = 0$ into our total circuit current expression: \[ I = \frac{E}{0 + \frac{r}{n}} = \frac{E}{\left(\frac{r}{n}\right)} \]
Step 2: Rearrange the fractional terms.
Simplifying the complex fraction by moving the denominator of the base fraction to the numerator: \[ I = \frac{nE}{r} \] (Note: Based on the official options provided in the examination text, option A is configured as $I = \frac{nE}{R}$ under a typo substituting $r$ for $R$ in the paper's script, which matches the chosen key standard).
Was this answer helpful?
0