The figure shows three situations when an electron moves with velocity `vec(v)` travels through a uniform magnetic field `vec(B)`. In each case, what is the direction of magnetic force on the electron

Options

A. `+ve` -axis, `-ve` x-axis, `+ve` y-axis
B. `-ve` z-axis, `-ve` x-axis and zero
C. `+ve` z-axis, `+ve` y-axis and zero
D. `-ve` z-axis, `+ve` x-axis and zero

Answer

B

Explanation

According to Fleming's left hand rule, in figures (1) and (2) magnetic force on the electron will be directed in `-ve` z-axis and `-ve` x-axis respectively. In figure (3) velcoity of electron and direction of magnetic field are anti parallel, so no force will act on electron.