An infinite solid cylindrical wire of radius R carries current I uniformly over its cross-section. At what distance from the centre is the magnetic field equal to μ₀I/(4πR)?

Question

G1 Physics · Accepted Answer

Inside the wire, B=μ₀Ir/(2πR²). Equating this to μ₀I/(4πR) gives r=R/2. (There is also an outside point r=2R, but among the given options the correct one is R/2.)