Question

How are the mass and charge of an electron deter­mined?

Answer 1

Electron:

The negatively charged particle that revolves in the shells of atom is known as an electron.

Determination of charge on electron:

1. The charge on the electron was determined by oil drop experiment.
2. The absolute charge on electron is $1$ coulomb of negative charge.
3. This suggests that an electron has $1$ unit of negative charge.
4. Thus, the relative charge on an electron is $-1$.

Determination of mass of electron:

1. The mass of electron is $\frac{1}{1840}$ times the mass of a hydrogen atom.
2. The mass of hydrogen atom is $1\mathrm{u}$.
3. Thus, the relative mass of electron is $\frac{1}{1840}\mathrm{u}$.
4. The absolute mass of electron is $1.9\times {10}^{-28}\mathrm{g}$ which is very small and considered as negligible.