Electric charge and current

Electric Charge and Current

Understanding Electric Charge

Electric charge is a fundamental property of matter. It is responsible for the electromagnetic force, one of the four fundamental forces in nature. There are two types of electric charges: positive and negative. Protons carry a positive charge, while electrons carry a negative charge. Neutrons, found in the nucleus of an atom, have no charge.

Like charges repel each other, while opposite charges attract. This interaction is described by Coulomb's law, which states that the force (F) between two charges (q_1 and q_2) is directly proportional to the product of the magnitudes of the charges and inversely proportional to the square of the distance (r) between them:

F = k × (|q_1 × q_2|) / r^2

Here, k is Coulomb's constant, approximately equal to 8.99 × 10^9 N·m²/C².

Electric Current

Electric current (I) is the flow of electric charge. It is measured in amperes (A). One ampere is defined as one coulomb of charge passing through a conductor in one second. The formula for electric current is:

I = Q / t

where Q is the charge in coulombs and t is the time in seconds.

For example, if 10 coulombs of charge pass through a wire in 5 seconds, the current is:

I = 10 C / 5 s = 2 A

Conductors and Insulators

Materials can be classified as conductors or insulators based on their ability to allow electric charge to flow. Conductors, such as metals like copper and aluminium, have free electrons that can move easily, allowing electric current to flow. Insulators, such as rubber and glass, do not have free electrons, making it difficult for electric current to pass through.

Direct Current (DC) and Alternating Current (AC)

Electric current can be classified into two types: direct current (DC) and alternating current (AC). In direct current, the flow of electric charge is in one direction only. Batteries provide DC. In alternating current, the flow of electric charge periodically reverses direction. The electricity supplied to homes and businesses is typically AC.

Measuring Electric Current

To measure electric current, an ammeter is used. An ammeter is connected in series with the circuit, meaning it is part of the circuit path. This allows it to measure the current flowing through the circuit accurately.

Ohm's Law

Ohm's law relates voltage (V), current (I), and resistance (R) in a circuit. It states that the current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance. The formula is:

V = I × R

For example, if a circuit has a current of 3 A and a resistance of 4 Ω, the voltage can be calculated as:

V = 3 A × 4 Ω = 12 V

Applications of Electric Current

Electric current has many applications in daily life. It powers devices such as lights, computers, and appliances. Understanding electric current is essential for working with electrical circuits safely and effectively.

Summary

• Electric charge comes in two types: positive and negative.
• Electric current is the flow of electric charge, measured in amperes (A).
• Conductors allow current to flow, while insulators do not.
• DC is current that flows in one direction, while AC periodically reverses direction.
• Ohm's law relates voltage, current, and resistance in a circuit.

Check your understanding

1. What is the unit of electric charge?
2. Explain the difference between conductors and insulators.
3. How would you calculate the current if 15 coulombs of charge pass through a circuit in 3 seconds?
4. What is the relationship between voltage, current, and resistance according to Ohm's law?