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Home  >>  JEEMAIN and AIPMT  >>  Physics  >>  Class12  >>  Current Electricity
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The length of the potentiometer wire is l. A cell of emf E is balanced at length $ \large\frac{l}{3}$ from the positive end of the wire. If the length of the wire is increased by $ \large\frac{l}{2}$, at what distance will the same cell give a balance point

$\begin {array} {1 1} (A)\;\large\frac{l}{3} & \quad (B)\;\large\frac{l}{2} \\ (C)\;\large\frac{2l}{3} & \quad (D)\;\large\frac{3l}{4} \end {array}$


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The student is expected to have an understanding of the construction of a potentiometer.
Potential gradient in the first case = $ \large\frac{E_0}{l}$
$ E=\large\frac{l}{3}$ $ \large\frac{E_0}{l}$ $ \large\frac{E_0}{3}$
In the second case $= \large\frac{2E_0}{\Large\frac{3l}{2}}$
$ E = (X) \large\frac{2E_0}{\Large\frac{3l}{2}}$
On solving these two equations, we get $ x = \large\frac{l}{2}$
Ans : (B)
answered Feb 8, 2014 by thanvigandhi_1
edited Mar 14, 2014 by thanvigandhi_1

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