A thin flexible wire of length L is connected to two adjacent fixed points and carries a current I in the clockwise direction. When the system is put in a uniform magnetic field of strength B going into the plane of the paper, the wire takes the shape of a circle. The tension in the wire is:
IBL
IBLπ
IBL2π
IBL4π
Solution:
2Tsin(dθ/2) = BiRdθ Tdθ = BiRdθ (for θ small) T = BiR = BiL/(2π)