question_answer

A potentiometer wire has length 4m and resistance\[8\Omega \]. The resistance that must be connected in series with the wire and an accumulator of emf 2V, so as to get a potential gradient 1mV per cm on the wire is:

A) \[48\Omega \]                

B) \[32\Omega \]  

C) \[40\Omega \]                

D) \[44\Omega \]

Correct Answer: B

Solution :

[b] \[For\text{ }1\text{ }cm\text{ }V\text{ }=\text{ }{{10}^{-3}}\text{ }volt\] \[For\,400\,cm,V=={{10}^{-3}}\times 400\] \[V=0.4\text{ }volt\] \[V=\frac{2}{8+R}\times 8\] \[0.4=\frac{16}{8+R}\] \[40=R+8\] \[R=32\Omega \]