Problem 7: A 0.2 m wire is bent into a circular shape and is placed in a uniform magnetic field of 2 T. If the current in the wire is 20 mA, then find the maximum torque acting on the loop.
Given Length of the wire = L = 0.2 m B = 2 T Current = I = 20 mA = 20 * 10-3A
Required Torque = τ =?
Strategy: Since τ = IBA, where A is area of the loop. We do not know the area of the circular shape therefore, first we find it.
When the 0.2 m long wire is bent in a circular shape, the circumference of the shape will also be 0.2 m. Therefore, apply formula C = 2πr to find radius of the circle.
Now area of a circle is = πr2, therefore,
Put this value (of area) in the formula for torque, given above,