Q: The length of a Potentiometer wire is 5 metres. An electron in this wire experiences a force of 4.8 × 10-19 N , e.m.f. of the main cell used in Potentiometer is :
(a) 3 volt
(b) 15 volt
(c) 1.5 volt
(d) 5 volt
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Ans: (b)
Sol: Force = electric intensity × charge
$ \displaystyle Force = \frac{Potential \; difference }{distance} \times charge $
$ \displaystyle 4.8 \times 10^{-19} = \frac{V}{5} \times 1.6 \times 10^{-19} $
V = 15 volt