UPSC NDA II 2023 General Ability Solved Paper

Concept:The Lorentz force on a moving charge in a magnetic field is always perpendicular to the velocity, so it does no work and cannot stop the motion.Explanation:For a charge $q$ moving with velocity $v$ through a magnetic field $B$, the Lorentz force is $F = qvB\sin\theta$.Here the field is perpendicular to motion, so $\theta = 90^\circ$ and $\sin\theta = 1$.The magnitude of force becomes $F = qvB$.This force is always perpendicular to the direction of motion.A perpendicular force changes only the direction of velocity, not its speed.Therefore, the speed of the charges remains constant.Both positive and negative charges experience the Lorentz force, but because the force is perpendicular, they do not slow down or stop.Additionally, the direction of the Lorentz force is the same for both positive and negative charges in this setup (the cross product $v \times B$ gives the same direction for both signs).Thus, the charges do not separate based on their sign.Since no other force opposes their motion, both positive and negative charges continue to move uninterrupted through the magnetic field.Answer:Both kind of charges will keep moving uninterrupted.