Question

Biot-Savart law indicates that the moving electrons (velocity $\vec{v}$ ) produce a magnetic field $\vec{B}$ such that

• A. $\vec{B}\perp \vec{v}$
• B. $\vec{B}||\vec{v}$
• C. it obeys inverse cube law
• D. it is along the line joining the electron and point of observation

Answer 1

Answer: (A)

Magnetic field produced by charges moving with velocity $\vec{v}$, at a distance $r$ is
$\vec{B}=\left(\frac{{\mu }_0}{4\pi }\right)\cdot q\frac{\vec{v}\times \hat{r}}{r^2}$.
Therefore $\vec{B}\perp \vec{v}$.