The particle with the minimum frequency of revolution when projected with the same velocity perpendicular to a magnetic field will be the one with the greatest mass, since the frequency (also known as the cyclotron frequency) is inversely proportional to the mass of the particle.
The cyclotron frequency (f) is given by the formula:
f = qB/2πm
Given the options:
- Alpha particles (α) are helium nuclei, consisting of 2 protons and 2 neutrons, with a mass of about 4 atomic mass units (amu).
- Beta particles (β) are electrons, with a much smaller mass of about 1/1836 of a proton's mass.
Since the mass of an alpha particle is much greater than that of a beta particle, the alpha particle will have the minimum frequency of revolution.
Therefore, the correct answer is (a) alpha.
