Lesson 1: Charge in nature

Video Lesson:

Competencies (MLC)

Dear Learners,

At the End of this lesson, you will be able to:-

• Distinguish between the two types of electric charges.
• Show that the total electric charge in an isolated system is conserved.
• Use conservation of charge to calculate quantities of charge transferred between objects.

Brainstorming question

When do you say that a body is charged positively?

Key Concept

Charge in Nature

Objects surrounding us (including people) contain large amounts of electric charge. There are two types of electric charge: positive charge and
negative charge. Protons have a positive charge, and electrons have a negative charge. If the same amounts of negative and positive charge are brought together, they neutralize each other and there is no net charge.
Positive and negative charges are present in neutral objects, but their numbers are equal. However, if there is a little bit more of one type of charge than the other, then the object is said to be electrically charged.

Unit of Charge

$$\begin{gathered} \text{The SI unit of electric charge is Coulomb (C).}\text{One coulomb (1 C) of charge is carried by}6.25\times {10}^{18}\text{electrons.} \\ \text{An electron possesses a negative charge of}1.6\times {10}^{-19}\text{C.} \\ \text{In electrostatics, you often work with charge in micro Coulombs (}1\mu \text{C = 1}\times {10}^{-6}\text{C)}\text{and nano coulombs (}1\text{nC = 1}\times {10}^{-9}\text{C).} \end{gathered}$$

Conservation of Charge

During electrification, electric charges are neither created nor destroyed but are transferred from one material to another. This is called the law of conservation of charge. There are some practical examples of charge transfer from one material to another. For example, have you ever seen the old comb and hair trick where your hair rises and sticks to the comb? This arises because of the simple conservation of charge, i.e., the transfer of charge either from the comb to the hair or vice versa. Thus, the total charge in an isolated system never changes. By isolated, you mean that no particles are allowed to cross the boundary of the system.

Quantization of Charge

The smallest charge that is possible to obtain is that of an electron or proton. The magnitude of this charge is denoted by e. Charge is said to be quantized when it occurs as the integral multiples of e. This is true for both negative and positive charges and is expressed as.

q = ne where n is positive or negative integer.