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Question: Answered & Verified by Expert
In a metre-bridge when a resistance in the left gap is 2 Ω and unknown resistance in the right gap, the balance length is found to be 40 cm. On shunting the unknown resistance with 2 Ω, the balance length changes by:
PhysicsCurrent ElectricityJEE MainJEE Main 2024 (01 Feb Shift 2)
Options:
  • A 22.5 cm
  • B 20 cm
  • C 62.5 cm
  • D 65 cm
Solution:
1995 Upvotes Verified Answer
The correct answer is: 22.5 cm

In first circuit:

For balanced condition, we get 240=X60X=3Ω

In second case:

Net resistance of the right side due to shunting becomes,  X'=2×32+3=1.2 Ω

Again for balanced condition, 

2=1.2100-

200-2=1.2

=2003.2=62.5 cm

Clearly, balance length changes by 22.5 cm.

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