Electric Charge – Learn

What is Electric Charge?

Electric charge is understood by considering the structure of an atom. Atoms have a nucleus consisting of positively charged protons and neutral particles called neutrons. Orbiting the nucleus are negatively charged electrons, which are attracted to the positively charged nucleus. With electrostatic forces, like charges repel and unlike charges attract.

How do objects become charged?

Atoms are neutral. This is because in any atom there are equal numbers of electrons and protons. Protons are held tightly to the nucleus but electrons are easier to be removed as they are in a cloud surrounding the nucleus. When an atom loses an electron it develops a positive net charge; when it gains an electron, it develops a negative net charge. When an atom gains or loses an electron it is known as an ion.

How do we measure charge?

The net charge is often referred to as the elementary charge. The letter q is used to represent the amount of charge. The SI unit of charge is the coulomb (C), where one coulomb is the charge on  6.25 \times 10^{ 18 } electrons or protons. Therefore, the charge of a proton ({ q }_{ p }) is equal to  1.6 \times 10^{ -19 } C and the charge of an electron ({ q }_{ e }) is  -1.6\: \times 10^{ -19 } C. The total charge can then be calculated by multiplying the number of particles by their specific charge.

The total charge can be calculated by multiplying the number of elementary particles by their specific charge:  { q }_{ n }={ n }_{ particles } \times  { q }_{ particle }

All electrically charged objects produce an electrostatic force on other objects that have an overall net charge. The electrostatic force causes like charges to repel and opposite charges to attract. The magnitude of the electrostatic force can be calculated using Coulomb’s law, which is discussed later.

Example 1:

If a neutral atom has gained an electron, how would we now describe this particle?


This particle is an ion with an overall negative net charge

Example 2:

How many electrons would make up a charge of -2.5C?


Using:  { q }_{ n }={ n }_{ e } \times { q }_{ e }

 { n }_{ e }=-2.5\div -1.6\times 10^{ -19 }

 { n }_{ e }=1.5625 \times 10^{ 19 }

Example 3: What would happen if two positively charged objects were brought close together?


They would exert a repulsive force on each other and tend to move away from each other.