Question

A long straight wire carries a current along the $y-$axis. One can find two points symmetrical about $y-$ axis in the $x-y$ plane such that

• A. the magnetic field vectors are equal.
• B. the directions of the magnetic fields are perpendicular to each other.
• C. the magnitude of the magnetic fields are equal, and the directions are perpendicular to each other.
• D. the field at one point is opposite to that at the other point.

Answer 1

The correct option is D the field at one point is opposite to that at the other point.

According to Biot-Savart Law,

$\overrightarrow{dB}=\frac{{\mu }_0}{4\pi }\frac{i\overrightarrow{dl}\times \overrightarrow{r}}{r^3}$


In $x-y$ plane, for two points symmetrical about $y-$ axis, $\overrightarrow{dB}$ will be in opposite direction from right-hand thumb rule.