Two concentric coils of 10 turns each are placed in the same plane. Their radii are 20 ~cm and 40 ~cm and carry 0.2 and 0.3 ~A . current respectively in opposite directions. The magnetic induction (in T) at the centre is

Step-by-step solution

Two coils carry currents in opposite directions, hence net magnetic field at centre will be difference of the two fields. ie, aligned B_ net & = ₀ 4 2 N [ i₁ r₁ - i₂ r₂ ] & = 10 ₀ 2 [ 0.2 0.2 - 0.3 0.4 ] & = 5 4 ₀ aligned