Question

What is the mass of an electron?

Answer 1

As the electron is quite small, its true mass changes as it moves, and we call that the relativistic mass.

`m_"rel" = m_"rest"/sqrt(1 - v^2/c^2)`

However, as the time-independent Schrodinger equation involves what are called stationary states, we tend to use its rest mass in calculations, defined as `m_e`:

`m_"rest" -= m_e = 9.10938291_(40)xx10^(-31) "kg"`,

where the subscript indicates the digits past the ones to which we are certain.