CBSE 2025 · Region 7 · Set 1 · Q13 · 1 mark

Assertion (A) : A charged particle is moving with velocity v in $\displaystyle \mathrm{x}-\mathrm{y}$ plane, making an angle $\displaystyle \theta\left(0<\theta<\frac{\pi}{2}\right)$ with $\displaystyle \mathrm{x}$-axis. If a uniform magnetic field $\displaystyle \overrightarrow{\mathrm{B}}$ is applied in the region, along $\displaystyle \mathrm{y}$-axis, the particle will move in a helical path with its axis parallel to x -axis. Reason $\displaystyle (R)$ : The direction of the magnetic force acting on a charged particle moving in a magnetic field is along the velocity of the particle.

CBSE Class 12 Physics past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.