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.