**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

\(q=ne\)

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

Solution:

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: \(6.4\times 10^{-16}\;C\)

Solution:

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

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

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