Question

What is the torque acting on a coil placed in a magnetic field of strength B?

Answer 1

In figure,

τ = F1 or F3 × XZ

τ =BI.lb.cosθ

τ =BI.A.cosθ

If there are ‘N’ turns of coil,

τ =BI.A.cosθ.N

∴ τ =BINAcosθ

This is the required relation.