⚡️ Electric charge is a fundamental property of matter that causes it to experience a force when placed in an electric field. There are only two kinds of charge: positive (+) and negative (−).
Imagine a crowd at a concert. Some people (positive charges) are standing on the left side, and others (negative charges) are on the right. When they move closer, the crowd feels a pull or push. This “pull” or “push” is the force between charges. The amount of people in each group represents the magnitude of the charge, written as \$q\$.
• Positive charge (+) is carried by protons in the nucleus of an atom.
• Negative charge (−) is carried by electrons that orbit the nucleus.
• Like charges repel: \$+ +\$ or \$- -\$ push away.
• Opposite charges attract: \$+ -\$ pull together.
🔋 Think of a magnet: north and south poles attract, but two north poles repel. Charges work the same way but with a different symbol.
The SI unit of charge is the coulomb (C).
One coulomb equals the charge of about \$6.24 \times 10^{18}\$ elementary charges:
\$1\,\text{C} = 6.24 \times 10^{18}\,e\$
In practice, we often use the symbol \$q\$ to represent any charge, positive or negative.
✔️ Remember:
| Charge type | Symbol | Example particle | Force with like charge | Force with opposite charge |
|---|---|---|---|---|
| Positive | \$+q\$ | Proton | Repel | Attract |
| Negative | \$-q\$ | Electron | Repel | Attract |