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Physics · 2025 · 3 marks
CBSE 2025 · Region 2 · Set 1 · Q22
(a) A cell of e. m. f. E and internal resistance r is connected with a variable external resistance R and a voltmeter showing potential drop V across…
(a)
A cell of e. m. f. E and internal resistance r is connected with a variable external resistance $\displaystyle \mathrm{R}$ and a voltmeter showing potential drop $\displaystyle V$ across R. Obtain the relationship between $\displaystyle V, \mathrm{E}, \mathrm{R}$ and r.
(b)
Draw the shape of the graph showing the variation of terminal voltage V of the cell as a function of current I drawn from it. How one can determine the e. m. f. of the cell and its internal resistance from this graph?
Marking-scheme solution
(a)
Current drawn from the cell $\displaystyle (I)=\frac{E}{r+R}$
Potential difference $\displaystyle (V)=I R$
$\displaystyle V=\frac{E R}{r+R}$
(b)
Slope of the graph is equal to internal resistance of the cell.
The intercept on Y-axis gives the emf of the cell.
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