Rankers Physics

Combination of Batteries: Practice Problem & Solution

A student measures the terminal potential difference ($V$) of a cell (of emf $\varepsilon$ and internal resistance $r$) as a function of the current ($I$) flowing through it. The slope, and intercept, of the graph between $V$ and $I$, then, respectively, equal: (2009)
$-r$ and $\varepsilon$
$r$ and $-\varepsilon$
$-\varepsilon$ and $r$
$\varepsilon$ and $-r$

Solution Explained:

To solve this problem, we apply the core principles of Combination of Batteries. Understanding the underlying formula is key to arriving at the correct answer below:

The terminal potential difference equation is $V = \varepsilon - Ir$, which can be rewritten as $V = -rI + \varepsilon$. Comparing this with the straight-line equation $y = mx + c$, the slope $m$ is $-r$ and the y-intercept $c$ is $\varepsilon$.

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