A potentiometer compares the EMFs of two cells. Cell 1 with $\varepsilon_1 = 1.5$ V gives a null length 75 cm. A cell 2 of unknown EMF gives a null length 50 cm. Its EMF is:
A0.50 V
B1.50 V
C1.00 V
D2.25 V
Answer & Solution
Correct answer: C. 1.00 V
$\varepsilon_1/\varepsilon_2 = \ell_1/\ell_2$ ⇒ $\varepsilon_2 = \varepsilon_1 \cdot \ell_2/\ell_1 = 1.5 \times 50/75 = 1.0$ V.
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