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Question: Answered & Verified by Expert
A horizontal metallic rod of mass m and length l is supported by two vertical identical springs of spring constant, K each and natural length l0. A current i is flowing in the rod in the direction shown. If the rod is in equilibrium then the length of each spring in this state is:

PhysicsMagnetic Effects of CurrentJEE Main
Options:
  • A l0+ilB-mgK
  • B l0+ilB-mg2K
  • C l0+mg-ilB2K
  • D l0+mg-ilBK
Solution:
2980 Upvotes Verified Answer
The correct answer is: l0+ilB-mg2K
The force on the rod due to the magnetic field and gravity is

ilB-mg  (upwards)

Hence the extension in the springs is ilB-mg2k

(Note that effective spring constant is 2k)

Therefore the length of the spring is l0+ilB-mg2k


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