Question 177: 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

Integer / Numeric Answer Type