2026 · Q54
A positively charged particle (alpha-particle) is projected towards west in a horizontal plane. It is deflected towards north in the same plane by a magnetic field. Which one among the following is the direction of the magnetic field?
General KnowledgePhysics
- ATowards south
- BTowards east
- CVertically downwards
- DVertically upwards
Explanation
The Lorentz force is F = q(v x B). The alpha particle has q > 0, velocity v toward the west and is deflected (force F) toward the north in the horizontal plane. With v pointing west, only a vertically upward magnetic field gives v x B pointing north (west x up = north). The answer is (D) vertically upwards.