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 z–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

(i) `vecF = q (vecv xx vecB) implies (hatk) = (- hati xx -hatj)`
(ii) `(-hati) = (-hatj xx hatk)`
(iii) `(0) = (-hatj xx hatj)`