The magnetic field at a distance of $2 \mathrm {~cm}$ from a long straight current-carrying wire is $4 \mu \mathrm { T }$. What is the magnetic field at a distance of $1 \mathrm {~cm}$ from this wire?
A) $6 \mu \mathrm { T }$
B) $8 \mu \mathrm { T }$
C) $2 \mu T$
D) $10 \mu \mathrm { T }$
E) $4 \mu T$

Question

Quizplus · Accepted Answer

The magnetic field $B$ around a long straight current-carrying wire varies inversely with the distance $r$ from the wire, according to the formula $B = \frac{\mu_0 I}{2\pi r}$, where $\mu_0$ is the permeability of free space and $I$ is the current. When the distance is halved (from $2 \mathrm{cm}$ to $1 \mathrm{cm}$), the magnetic field doubles. Therefore, if the magnetic field at $2 \mathrm{cm}$ is $4 \mu \mathrm{T}$, at $1 \mathrm{cm}$ it would be $8 \mu \mathrm{T}$.

The Magnetic Field at a Distance Of 2 cm2 \mathrm {~cm}2 cm From a Long Straight Current-Carrying Wire Is

The Magnetic Field at a Distance Of $2 \mathrm {~cm}$ From a Long Straight Current-Carrying Wire Is