Answer :

As the potentiometer wire has uniform cross section throughout, the potential difference between X and any point at a distance l from A till point Y is,

V (l)= k l

where k is the potential drop per unit length, As the positive terminal of E_{1} is connected to X and on touching the jockey near to the end X of the potentiometer wire, the galvanometer pointer deflects to left and on touching the jockey near to end Y of the potentiometer, the galvanometer pointer again deflects to left but now by a larger amount, this indicates that the cell E_{1} is of larger emf than E which indicates that the galvanometer will never show zero deflection. For a galvanometer to show zero deflection somewhere on XY the emf of E > E_{1}

**OR**

a) **Formula:** **-**

The meter bridge uses the concept of a balanced Wheatstone bridge to find the value of the unknown resistor so that the formula can be written as,

Where,

X is the unknown resistance,

R is the resistance of the resistance box,

L_{AB} is the length of wire where till the null point is found.

It is written as to fulfill the condition for the balanced bridge.

b) The above formula can be re-written as

The above expression indicates that if the value of R is increased then the value of l_{AB} will increase.

**Conclusions: -**

The value of **x** can be found as,

The value of **R** increases then the value of **l _{AB}** also increases.

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