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Question

A length of 150 cm of a potentiometer wire is required to balance the emf of a cell. When a 5Ω resistor is connected across the terminals of the cell, the length required for balance is 125 cm. The internal resistance of the cell is

A
1 ohm
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B
1.1 ohm
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C
1.2 ohm
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D
1.3 ohm
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Solution

The correct option is D 1 ohm
Given,
Length of the potentiometer wirel1=150cm
Resistance R=5Ω
balancing length is obtained at l2=125cm
Internal resistance r=?
we have,

r=R[l1l21]

=5[1501251]

=5[25125]

=1Ω

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