Two concentric vertical circular coils X and Y have radii 16 cm and 10 cm. X: 20 turns, 16 A; Y: 25 turns, 18 A. Their currents are opposite as viewed from west. If the net field is (π/α) mT, find α.
Physics · Magnetic effect of current
JEE Mains

Question

Two concentric vertical circular coils X and Y have radii 16 cm and 10 cm. X: 20 turns, 16 A; Y: 25 turns, 18 A. Their currents are opposite as viewed from west. If the net field is (π/α) mT, find α.

Physics · Magnetic effect of current

G1 Physics · Accepted Answer

At the common centre B=μ₀NI/(2R). For X, NI/(2R)=1000 A/m; for Y it is 2250 A/m. Currents are opposite, so net=1250μ₀=5π×10⁻⁴ T=(π/2) mT. Thus α=2.