current-electricity Question 52

Question: Q. 4. Draw a circuit for determining internal resistance of a cell using a potentiometer. Explain the principle on which this method is based.

U] [SQP II 2017]

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Solution:

Ans.

(ii) If key K2 is open and key K1 is closed and null point is obtained at a distance l1 from Q,

(i)E=Kl1

If key K2 is closed and key K1 is open and null point is obtained at a distance l2 from Q,

(ii)V=Kl2

On dividing equation (i) by (ii)

EV=l1l2 R+rR=l1l2 r=(l1l2l2)R

where,

R= shunt resistance in parallel with the cell, l1 and l2= balancing length without and with shunt r= internal resistance of the cell

[CBSE Marking Scheme, 2017]



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