A) 3.5 m
B) 3 m
C) 2.75 m
D) 2.0 m
Correct Answer: C
Solution :
Resistance of potentiometer wire \[R=\rho \times \frac{l}{A}\] or \[R=\left( \rho \times \frac{10}{A} \right)\] The value of \[2.5m\]length wire \[R=\frac{\rho \times 10}{A\times 10}\times 2.5\] or \[R=\left( \frac{2.5\rho }{A\times 10} \right)\] Potential \[V=I\times R\] \[=I\left( \frac{2.5\rho }{A\times 10} \right)\] Now again the length of potentiometer wire is incased by 1 m, then resistance of null position wire. \[R=\left( \frac{\rho \times l}{11\times A} \right)\] \[V=IR\] and \[V=V\] \[\frac{I\times 2.5\rho }{A\times 10}=\frac{\rho \times l}{11\times A}\times I\] or \[\frac{2.5\times 11}{10}=l=2.75m\]
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