First slide

Ohm's law

Question

The cell has an emf of 2 V and the internal resistance of this cell is $0.1 Ω .$ It is connected to resistance of $3.9 Ω$ , the voltage across the cell will be

Moderate

A

1.5 V
B

2 V
C

1.95 V
D

1.8 V

Solution

The voltage across cell terminal will be given by
$V = E - i r$
where r is internal resistance.
Also current, $i = \frac{E}{R + r}$
$∴ V = E - (\frac{E}{R + r}) r$
Putting the numerical values, we have
$\begin{array}{l} E = 2 V, r = 0 .1 Ω, R = 3 .9 Ω \\ V = 2 - (\frac{2}{3 .9 + 0 .1}) \times 0 .1 \end{array}$
V = 1.95 V

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