Electric Charge

Atoms make up matter. There are three subatomic particles of the atom namely, protons, neutrons, and electrons. The atom has a nucleus at its center where the proton – a positively charged particle and the neutron – a particle with zero charge are located. The electrons – negatively charged particle orbits around the atom.

Mostly, atoms are neutral. This means that the atoms contain the same number of protons and electrons giving it a zero net charge. However, an atom can lose or gain electrons. An atom which loses electron is a positive ion and the one that gains electron is a negative ion.

The unit of a charge is Coulombs, \(C\). The charge of the proton is \(1.6 \times 10^{-19}\; C\) and the electron has \(-1.6 \times 10^{-19} \;C\). This value is also called as elementary charge symbolized by the letter \(e\). Thus, the proton’s and electron’s charge can also be expressed as \(+e\) and \(-e\).

\(q\) is the symbol for charge. The total charge of an object is the number of particles multiplied by its charge. Mathematically written as


where \(q\) is the total charge, \(n\) is the number of particles and \(e\) is the charge of the particle.

Example 1.

An object has an excess electron of \(5.0\times 10^4\) electrons. What is its net charge?

Given: \(n=5.0\times 10^4\;\text{electrons}\)


To solve for the net charge, we use the formula \(q=ne\)

\(q=(5.0\times 10^4)( -1.6 \times 10^{-19} \;C)=-8.0\times 10^{-15}\;C\)

The net charge of the object is \(-8.0\times 10^{-15}\;C\).

Example 2.

How many protons pass through an object if its total charge is \(6.4\times 10^{-16}\;C\)?

Given: \(6.4\times 10^{-16}\;C\)


\(q=ne \implies n=\frac qe\)

\(n=\frac{6.4\times 10^{-16}\;C}{1.6 \times 10^{-19} \;C }=4.0\times 10^3 \;\text{protons}\).

There are \(4.0\times 10^3\) protons pass through the object.