Understanding Electric Charge and Current

What is Electric Charge?

Electric charge is a fundamental property of matter. It comes in two varieties - positive and negative. Opposite charges attract each other while like charges repel. The unit of charge is the coulomb (C).

Conservation of Charge

One of the basic laws of electromagnetism states that electric charge can neither be created nor destroyed - it is always conserved. During any process, the total charge before must equal the total charge after.

Electric Current

Current is the rate of flow of electric charge. Conventional current is the flow of positive charge, while electron flow represents the actual movement of negatively charged electrons through a material.

The relationship between current I, charge Q, and time t is given by:

I = Q/t

Example: Calculating Current

Problem: An amount of 6 C of charge passes through a wire in 3 s. Find the current.

Solution:

• Given: Q = 6 C, t = 3 s
• Using I = Q/t
• I = 6 C / 3 s = 2 A

Conductors and Insulators

Materials can be classified into conductors and insulators based on their ability to conduct electric current:

• Conductors have high electrical conductivity and allow charge to flow freely (e.g. metals).
• Insulators resist the flow of charge and have low electrical conductivity (e.g. plastics, rubber).

Electrical Conduction in Metals

In metals, some outer electrons are free to move and carry charge through the material. When a voltage is applied across a metal, these free electrons drift, creating an electric current.

Circuit Symbols and Conventions

Standard symbols are used in circuit diagrams to represent different electrical components:

• Cell or battery:
• Resistor:
• Ammeter:

The flow of conventional current in a circuit is shown using arrowheads.