In a cyclotron, a charged particle:

The correct answer is Option (1) → undergoes acceleration all the time.

In a cyclotron the magnetic field only bends the path of the particle into a semicircle inside each dee, and the oscillating electric field in the gap between the dees increases its speed each time it crosses. Acceleration is a change of velocity, in magnitude or in direction.

Option (1) undergoes acceleration all the time — Correct. Inside a dee the speed is constant but the direction changes continuously, so there is a centripetal acceleration \( v^{2}/r \); in the gap the electric force speeds it up.

Option (2) speeds up between the dees because of magnetic field — Incorrect. The speed is increased by the electric field; a magnetic force is always perpendicular to the velocity and does no work.

Option (3) speeds up in a dee — Incorrect. The metal dee shields its interior from the electric field, so the speed stays constant there.

Option (4) slows down within a dee and speeds up between the dees — Incorrect. The particle does not slow down inside a dee; it moves with constant speed.

Note: A similar question was also asked in CUET (UG) 2023 on 14-06-2023 (Slot 2) and on 13-06-2023 (Slot 3).

NCERT Exemplar:
Moving Charges and Magnetism – …