As a cell ages, its internal resistance increases. A voltmeter of resistance 270 Ω connected across an old dry cell reads 1.44 V. However, a potentiometer at the balance point, gives a voltage measurement of the cell as 1.5 V. Internal resistance of the cell is……… + 5.25 Ω.
Text Solution
Verified by ExpertsCHECK THE SOLUTION.
(6)
Sol.
Voltage measured by potentiometer, at the balance point, is the emf. This is because current drawn from the cell, at the balance point is zero.
Hence E = 1.5 V
If a voltmeter of resistance 270 Ω is connected across the cell as shown,
I = 
and voltage measured by the voltmeter
V = IR V (also V = E – Ir = 1.5 – Ir)
or V = 
270 but V = 1.44 V (given)
∴ 
270 = 1.44
or = 11.25 Ω
Prepare Smarter with CGP Edu
Get practice questions, solutions, and test series in one place.
Write a Review
Share your experience with this question and solution.
Commentary
Send your comment, doubt, correction, or feedback to admin.
Similar Questions
Explore conceptually related problems