Question

Particles and their antiparticles have
A) Same masses but opposite spins
B) Same masses but opposite magnetic moments
C) Same masses and same magnetic moments
D) Opposite spins and same magnetic moments

Answer 1

Hint: Antiparticles are particles having certain characteristics and properties, similar to those of their corresponding particles. At the same time, antiparticles also have certain characteristics and properties, just the opposite to those of their corresponding particles. An example of a particle antiparticle system is electron-positron. Mass of a particle refers to the heaviness of that particle. Spin of a particle refers to the intrinsic angular momentum of that particle. Magnetic moment of a particle gives an idea about the orientation of the particle in the presence of a magnetic field.

Complete step by step answer:
An antiparticle of a particle is a particle, which has certain similar characteristics as that of the particle itself. At the same time, it also has certain characteristics opposite to that of the particle. Similar characteristics shared by both particles and its antiparticle involve their masses as well as spins. On the other hand, dissimilar characteristics between a particle and its antiparticle involve their charges and magnetic moments. To give an example, positron is an antiparticle of an electron.
Mass of a particle refers to the heaviness of the particle. Considering the above-mentioned example of an electron-positron system, we know that masses of both these particles are the same and equal to $9.11\times {{10}^{-31}}kg$. At the same time, spins of both positron and electron are also the same and equal to $\dfrac{1}{2}$. Here, spin refers to the intrinsic angular momentum of a particle, which gives an idea about the number of symmetrical facets, the particle has, in one complete rotation. On the other hand, charge of an electron is given by $-1e$ whereas the charge of a positron is given by $+1e$.
Magnetic moment of a particle is proportional to the spin of the particle, and gives an idea about the orientation of the particle in the presence of a magnetic field. Moreover, it is also proportional to the charge of the particle. Mathematically, magnetic moment $(\mu )$ of a particle of charge $(q)$ with spin $(S)$ is given by
$\mu =\dfrac{q{{g}_{s}}S}{2m}$
where
$\mu $ is the magnetic moment of a particle
$q$ is the charge of the particle
$S$ is the spin of the particle
$m$ is the mass of the particle
${{g}_{s}}$ is the spin g-factor, a dimensionless quantity
Let this be equation 1
It is clear from equation 1 that the magnetic moment of an electron is negative while that of a positron is positive. Hence, we can conclude that magnetic moments of a particle and its antiparticle are opposite to each other.

So, the correct answer is “Option B”.

Note: From the definition, it is clear that a particle and its antiparticle have opposite charges. If we consider both these particles to be a pair, to form a system, a process called annihilation occurs. Annihilation is a process which talks about the conservation of total charge of a particle antiparticle system. It also involves the production of photons. For example, in an electron-positron system, the electron collides with the positron, to produce two photons. This process or collision between an electron and a positron in an electron-positron system, to produce photons is termed as annihilation.