A long, straight, current-carrying wire runs across the floor in a lab. At a distance of 0.250.25 meters from the wire, the magnetic field due to the wire is found to be 2.75~ / mu / text{T}2.75 μT and directed into the floor. What is the magnitude of the magnetic field at a distance of 0.750.75 meters from that same wire?

B = 916.7ηT or 916.7 * 10^-9 or 0.0000009167

Explanation:

Magnetic field due to a current carrying conductor is given by

B = μI / (2πr)

B: magnetic field

μ: permeability of free space

r: perpendicular distance from the wire

For r = 0.25, B = 0.00000275

0.00000275 = μI / (2π*0.25)

μI / (2π) = 0.0000006875

For r = 0.75

B = μI / (2πr)

B = 0.0000006875/0.75

B = 916.7ηT or 916.7 * 10^-9 or 0.0000009167