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Current Electricity — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsCurrent Electricity2 Marks
Question
A cell of emf ‘E’ and internal resistance ‘r’ is connected across a variable resistor ‘R’. Plot a graph showing variation of terminal voltage ‘V’ of the cell versus the current ‘I’. Using the plot, show how the emf of the cell and its internal resistance can be determined.
✓

Answer

The relation between V and I is
$V = E – Ir$
Hence, the graph, between V and I, has the form shown below.

For point $A, I=0$, Hence, $V_A= E$
For point B, V=0, Hence, $E=I_Br$
Therefore, $\text{r} =\frac{\text{E}}{\text{I}_{B}}$
Alternate Answer
Emf (E) equals the intercept on the vertical axis. Internal resistance (r) equals the negative of the slope of the graph.

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