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

Options

A. `B bot upsilon .`
B. `B || upsilon`.
C. it obeys inverse cube law.
D. it is along the line joing the electron and point of observation.

Answer

A

Explanation

In Biot-Savart.s law, magnetic field `B|| idl xx r` and idl due to flow of electron is in opposite direction of `upsilon` and by direction of cross product of two vectors, B.
`dB = (I.dl sin theta)/(r^(2))`
or
`dB = (I xx dl)/(r)`
According to Biot-Savart law, if magnetic field is not perpendicular to the motion of charge, then it will not move in helical path, which is not possible for motion of a charge in magnetic field. So, the magnetic field is perpendicular to the direction of flow of charge verifies answer .A..