• # question_answer Potentiometer wire PQ of 1 m length is connected to a standard cell ${{E}_{1}}.$ Another cell ${{E}_{2}},$ of emf 1.02 V is connected as shown in the circuit. Diagram with a resistance, r and a switch, S. With switch S open, null point is obtained at a distance of 51 cm from P.  Potentiometer Calculate (i) potential gradient of the potentiometer wire. (ii) emf of the cell ${{E}_{1}}.$ (iii) when switch S is closed, will null point moves towards P or towards Q ? Give reason,

 Given, ${{E}_{2}}=1.02V,$ ${{l}_{1}}=1\,m=100\,cm$ and ${{l}_{2}}=51\,cm$ (i) Potential gradient, $K=\frac{{{E}_{2}}}{{{l}_{2}}}=\frac{1.02\,V}{51\,m}=0.02\,V\,c{{m}^{-1}}$ (ii) ${{E}_{1}}=K{{l}_{1}}=(0.02\,Vc{{m}^{-1}})\times 100cm\Rightarrow {{E}_{1}}=2\,V$ (iii) Mo, when switch S is closed, position of the null point remains unaffected as no current flows through the cell $({{E}_{2}})$ at null points.