A circular loop of wire with radius of 1.0 m lies in the xy plane. A uniform 1.0 T external magnetic field is directed along the z axis. The wire is a conductor, and carries current of 1.0 Amperes. What is the tension (or compression) in the wire due to the external field?
The loop may be divided into a large number of small length
elements. When a current I is passed through the loop placed in the
magnetic field such that the plane of the loop is perpendicular to
field, then force on each element is
dF=Idl×B=IdlBsin90o=IdlB
Perpendicular to current element Idl as well as magnetic field
B. Hence, the loop opens into a circle.
Consider an element of length dl of circle of radius r, making an angle alpha at centre.
If T is the tension in the wire, then force toward
centre:
2Tsin2α=IBdl
For small angle α,sin2α=2α
2T⋅2α=IBdl
T=αIBdl=IBr(∴α=rdl)
=IB(2π1)(∴l=2πr)
=1×1×(2×3.14×1)=6.28N
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