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is made of uniform material and cross-sectional area, and it has uniform resistance per unit length. The potential gradient depends upon the current in the wire.
A potentiometer with a cell of emf `2 V` and internal resistance `0.4 Omega` is used across the wire `AB`. A standard cadmium cell of emf `1.02 V` gives a balance point at `66 cm` length of wire. The standard cell is then replaced by a cell of unknows emf `e` (internal resistance `r`), and the balance. Point found similarly turns out to be `88 cm` length of the wire. The length of potentiometer wire `AB` is `1 m`.
If the resistance is connected across the cell `e`, the balancing length will

A

increases

B

decrease

C

remain same

D

none

Text Solution

Verified by Experts

The correct Answer is:
B
`(e)/(1.02) = (88)/(66)` or `e = 1.36 V`
`4V` is greater than applied emf `2 V`, hence no balance point is obtained. On connecting the resistance across `e`, current will flow in `e` due to which terminal potential difference will be less than emf and the balancing length will decreases.
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