Electric Charge
Simple Explanation
Electric charge is a fundamental property of matter that comes in two types: positive and negative. Like charges repel each other; unlike charges attract each other. Charge is measured in coulombs (C). A neutral object has exactly equal amounts of positive and negative charge, which cancel out.
Why Do We Need It?
The simple rule "like repels, unlike attracts" is the foundation for understanding every electrical phenomenon in this chapter, from why a charged balloon sticks to a wall, to how lightning forms.
Worked Example
Predict the force between two charged objects
Two small charged spheres are brought near each other. Sphere A carries a positive charge; sphere B carries a negative charge. Predict what happens.
Why Does This Work?
This attraction/repulsion rule reflects the underlying electric field each charge creates — a positive charge's field pulls negative charges inward and pushes positive charges away, and vice versa for a negative charge's field.
Real-Life Example
A charged balloon sticking to a wall
Rubbing a balloon on your hair charges it, and it then sticks to a wall.
The charged balloon induces an opposite charge on the nearby surface of the (normally neutral) wall, and this induced unlike charge then attracts the balloon, holding it in place.
Practice
Two objects both carry a negative charge. What happens when they are brought close together?
EasyCommon mistake
Assuming any charged object attracts any other object — a charged object repels objects with the SAME sign of charge, and only attracts objects with the OPPOSITE sign (or neutral objects, via induction).
Quick Review
- Two types of charge: positive and negative.
- Like charges repel; unlike charges attract.
- Charge is measured in coulombs (C).