Question 435: Current Electricity

Question

A potentiometer wire of length $$300 \mathrm{~cm}$$ is connected in series with a resistance 780 $$\Omega$$ and a standard cell of emf $$4 \mathrm{V}$$. A constant current flows through potentiometer wire. The length of the null point for cell of emf $$20\, \mathrm{mV}$$ is found to be $$60 \mathrm{~cm}$$. The resistance of the potentiometer wire is ____________ $$\Omega$$.

Accepted Answer

$$l = 300$$ cm
$$\varepsilon  = Kx$$
$$20 	imes {10^{ - 3}} = \left( {{{4 	imes R} \over {780 + R}} 	imes {1 \over {300}}} ight)60$$
$$R = 20$$

Current Electricity

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