Question

As shown in the figure, a potentiometer wire of resistance 20 Ω and length 300 cm is connected with resistance box (R.B.) and a standard cell of emf 4 V. For a resistance ‘R‘ of resistance box introduced into the circuit, the null point for a cell of 20 mV is found to be 60 cm. The value of ‘R ‘ is Ω.

Answer 1

E= $\frac{AC}{AB(V_A-V_B)}$
∴ 20×10−3= $\frac{60}{300}$× 4×$\frac{20}{R+20}$
​∴ R=780 Ω