Question

Rest mass of a \[\beta \] particle is
\[A.\,1.6\times {{10}^{-19}}kg\]
\[B.\,9.1\times {{10}^{-31}}kg\]
\[C.\,2\times {{10}^{2}}kg\]
\[D.\,1\times {{10}^{5}}kg\]

Answer 1

Hint: The question is based on the concept of the beta particle. As the rest mass of a particle equals the mass of a particle when it is stationary, so, we will find the mass of a particle when it is not moving. An electron itself is a beta particle, thus, we will find the rest mass of an electron.

Complete answer:
Let us first know the meaning of the rest mass and then we will go through the rest mass of the beta particle.
Rest mass is the value of the mass of a particle when it is stationary or is not moving. Thus, every particle will have its own rest mass. The moving particles will have different mass, as they have the kinetic energy that is equivalent to that of the mass. So, the rest mass is different from that of the original mass of a particle. This rest mass of every particle depends on its kinetic energy.
A beta particle is a particle having high energy. Basically, a beta particle is an electron with high speed. We know that the mass of the electron is \[9.1\times {{10}^{-31}}kg\]. Thus, the rest mass of a beta particle equals the value of the mass of the electron, that is, \[9.1\times {{10}^{-31}}kg\].
\[\therefore \] The rest mass of a beta particle equals \[9.1\times {{10}^{-31}}kg\].
As, the rest mass of a beta particle equals the value of \[9.1\times {{10}^{-31}}kg\].

So, the correct answer is “Option B”.

Note: In the given options, the unit of the rest mass is given in terms of the kg. Even, they can ask for the options, in terms of the mega-electron volt. In such a case, we need to know the conversion formula to convert the rest mass from one unit to the other.