A positive charge is moving vertically upwards. When it enters a region of magnetic field directed towards north, the direction of force on the charge would be
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → West
The force on a moving charge is the Lorentz magnetic force \( \vec{F} = q\,\vec{v}\times\vec{B} \), perpendicular to both \( \vec{v} \) and \( \vec{B} \).
Take \( \hat{\imath} \) towards east, \( \hat{\jmath} \) towards north and \( \hat{k} \) vertically upwards.
\( \vec{v} = v\,\hat{k} \)
\( \vec{B} = B\,\hat{\jmath} \)
\( \displaystyle \vec{F} = q v B\,(\hat{k}\times\hat{\jmath}) = -\,q v B\,\hat{\imath} \)
For a positive \( q \) the force is along \( -\hat{\imath} \), that is towards the west.
NCERT (2026-27):
Magnetic Field, Lorentz Force – “… The force acts in a (sideways) direction perpendicular to both the velocity and the magnetic field. Its direction is given by the screw rule or right hand rule for vector (or cross) product as illustrated in Fig. 4.2.”