A very long straight current-carrying wire produces a magnetic field of 20 mT at a distance d from the wire.To measure a field of 5 mT due to this wire,you would have to go to a distance of:

Question

Quizplus · Accepted Answer

The magnetic field produced by a current-carrying wire decreases with distance according to an inverse-square law. Therefore, if we reduce the distance by a factor of x, the magnetic field will increase by a factor of x^2. To go from 20 mT to 5 mT, we need to reduce the magnetic field by a factor of 4. This means we need to increase the distance by a factor of 2 (since 2^2 = 4). Therefore, the distance we need to go to measure a field of 5 mT is 2d. The correct answer is choice C.

A Very Long Straight Current-Carrying Wire Produces a Magnetic Field