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Question: Answered & Verified by Expert
A conductor lies along the z-axis at - 1.5 z <1.5 m  and carries a fixed current of 10.0 A in - a ^ z  direction (see figure). For a field B = 3.0 × 1 0 - 4  e - 0.2x  a ^ y  T, find the power required to move the conductor at constant speed to x = 2.0 m, y = 0 m in 5 × 1 0 - 3  s . Assume parallel motion along the x-axis.

   
PhysicsMagnetic Effects of CurrentJEE MainJEE Main 2014 (06 Apr)
Options:
  • A 1.57 W
  • B 2.97 W
  • C 14.85 W
  • D 29.7 W
Solution:
1529 Upvotes Verified Answer
The correct answer is: 2.97 W
Power P = W Δ t

Force on conductor
F=I(l×b)

F =-10( 3 a ^ z )×( 3× 10 4 e 0.2x a ^ y )

F=90×10-4(e-0.2x) along with x-axis

work done on the conductor in moving along x-axis.

W=x=02F.dx

W = 0 2 Bi dx = 0 2 3 × 10 - 4 e - 0.2x × 3 × 10dx =90×10-4e-0.2x-0.202

= 450 × 10 - 4 [ 1 - e - 0.4 ] = 180 × 10 - 4 ( Using e - x = 1 - x )

P = W Δ t = 180 × 10 - 4 5 × 10 - 3 = 3.6 W.

Hence, closest option is 2.97 W.
(if we used exact value of exponential term will get exact answer).

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