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Figure 3.35 shows a 2.0 V potentiometer used for the determination of internal resistance of a 1.5 V cell. The balance point of the cell in open circuit is 76.3 cm. When a resistor of 9.5 Ω is used in the external circuit of the cell, the balance point shifts to 64.8 cm length of the potentiometer wire. Determine the internal resistance of the cell.

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Class 12 Physics
CBSE and UP Board
Current Electricity
Additional Exercise
Chapter-3 Exercise 3.24

NCERT Solutions Class 12 Physics Chapter 3 Question 24

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1 Answer

  1. Internal resistance of the cell = r

    Balance point of the cell in open circuit, l₁ = 76.3 cm

    An external resistance (R) is connected to the circuit with R = 9.5 Ω

    New balance point of the circuit, l₂ = 64.8 cm

    Current flowing through the circuit = I

    The relation connecting resistance and emf is,

    r = (l₁ -l₂ )/l₂ x R

    = (76.3 -64.8)64.8 x 9.5 =1.68 Ω

    Therefore, the internal resistance of the cell is 1.68Ω.

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