Question 481: Current Electricity

Question

The balancing length for a cell is 560 cm in a potentiometer experiment. When an external
resistance of 10 $$\Omega $$ is connected in parallel to the cell, the balancing length changes by 60 cm. If
the internal resistance of the ceil is $${N \over {10}}$$
$$\Omega $$ , where N is an integer then value of N is .............

Accepted Answer

Let the emf of cell is $$\varepsilon $$ internal resistance is 'r' and potential gradient is x.
When only cell connected :
$$\varepsilon $$ = 560x .....(1)
After connecting the resistor
$${{\varepsilon  	imes 10} \over {10 + r}}$$ = 500x ....(2)
from (1) and (2)
56 = 50 +5r
r = $${6 \over 5}\Omega $$ = $${N \over {10}}\Omega $$
$$ \Rightarrow $$ N = 12

Current Electricity

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