In a cyclotron a charged particle:
A. undergoes acceleration all the time
B. speeds up between the dees because of the magnetic field.
C. speeds up in dee
D. slows down within a dee and speeds up between dees

Hint: Firstly we will see cyclotron is a device used to accelerate charged particles like protons, deuterons and alpha particles to very high energy. In a cyclotron it is the electric field which accelerates the charge particles.

Complete step by step answer:
In a cyclotron, charged particles experience force due to electric field between the Dees and magnetic force ( force due to magnetic field ) while circulating inside the Dees. That is it always experiences a centripetal force.
Therefore it always accelerates.
Hence the correct option is A.

Additional information:
Uses of cyclotron:
1. The high energy particles produced in a cyclotron are used to bombard nuclei and study the resulting nuclear reactions and hence investigate nuclear structure.
2. The high energy particles are used to produce other high energy particles such as neutrons by collisions. These fast neutrons are used in atomic reactors.
3. It is used to implant ions into solid and modify their properties and synthesise new material.
4. It is used to produce radioactive isotopes which are used in hospitals for diagnosis and treatment.

Note:
Principle of a cyclotron: A charged particle can be accelerated to very high energies by making it pass through a moderate electric field large no. of times. This can be done with the help of a perpendicular magnetic field which throws charge particles into circular motion.
The magnetic field does not change the speed, it only makes the charge particles to cross the same electric field again and again by making it move along a circular path.
A large increase in the energy of a cyclotron increases the velocity to a very large extent. This throws the electrons out of step with the oscillating field.
Neutrons being electrically neutral cannot be accelerated by the cyclotron.