Electron rest mass

The electron rest mass (symbol: me) is the mass of a stationary electron, also known as the invariant mass of the electron. It is one of the fundamental constants of physics. It has a value of about 9.109×10−31 kilograms or about 5.486×10−4 atomic mass units, equivalent to an energy of about 8.187×10−14 joules or about 0.5110 MeV. The electron rest mass (symbol: me) is the mass of a stationary electron, also known as the invariant mass of the electron. It is one of the fundamental constants of physics. It has a value of about 9.109×10−31 kilograms or about 5.486×10−4 atomic mass units, equivalent to an energy of about 8.187×10−14 joules or about 0.5110 MeV. The term 'rest mass' is sometimes used because in special relativity the mass of an object can be said to increase in a frame of reference that is moving relative to that object (or if the object is moving in a given frame of reference). Most practical measurements are carried out on moving electrons. If the electron is moving at a relativistic velocity, any measurement must use the correct expression for mass. Such correction is only substantial for electrons accelerated by voltages of well over 100 kV. For example, the relativistic expression for the total energy, E, of an electron moving at speed v {displaystyle v} is where the Lorentz factor is γ = 1 / 1 − ( v / c ) 2 {displaystyle gamma =1/{sqrt {1-(v/c)^{2}}}} . In this expression me is the 'rest mass', or more simply just the 'mass' of the electron. This quantity me is frame invariant and velocity independent. However, some texts group the Lorentz factor with the mass factor to define a new quantity called the relativistic mass, mrelativistic = γme. This quantity is evidently velocity dependent, and from it arises the notion that 'mass increases with speed'. This construction is optional, however, and adds little insight into the dynamics of special relativity.