1.

In the figure, the potentiometer wire AB of length L and resistance 9r is joined to the cell D of emf ℰ and internal resistance r. The emf of the cell C is ℰ/2 and its internal resistance is 2r. The galvanometer G will show no deflection when the length AJ is(a) 4L/9 (b) 5L/9 (c) 7L/18 (d) 11L/18

Answer»

Correct Answer is: (b) 5L/9

In the position of balance,

current in AB is i = /10r .

p.d. across AB is i x 9r = 9/10 .

 p.d. per unit length of AB is 9/10L .

For balance,

/2 = (AJ) 9/10L 

or AJ = 5L/9 . 



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