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Question: Answered & Verified by Expert
A null point is found at 200 cm in potentiometer when cell in secondary circuit is shunted by 5 Ω. When a resistance of 15 Ω is used for shunting null point moves to 300 cm. The internal resistance of the cell is ______ Ω.
PhysicsCurrent ElectricityJEE MainJEE Main 2023 (29 Jan Shift 2)
Solution:
1003 Upvotes Verified Answer
The correct answer is: 5

Let potential gradient be x.

For the first case, we can write

εr+5×5=200x ......(1)

and after adding resistance, we can write

εr+15×15=300x .....(2)

From both equations, we get

r=5 Ω

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