Biot-Savart law indicates that the moving electrons (velocity `vecv` ) produce a magnetic field `vecB` such that

Options

A. `vecB_|_vecv`
B. `vecB||vecv`
C. it obeys inverse cube law
D. it is along the line joining the electron and point of observation

Answer

A

Explanation

According to Biot Savar's law, the magnetic field `vecB` at a point distance r from a charge q moving with a velocity `vecv` is given by, `vecB=(mu_0)/(4pi)(q(vecvxxvecr))/(r^3)` or `B=(mu_0)/(4pi)(vsintheta)/(r^2)`
The direction of `vecB` is along `(vecvxxvecr)`, i.e., perpendicular to the plane containing `vecv` and `vecr`. `vecB` at a point obeys inverse square law and not inverse cube law.