State that positive charges repel other positive charges, negative charges repel other negative charges, but positive charges attract negative charges

4.2.1 Electric Charge

What is Electric Charge?

Electric charge is a property of matter that makes it feel a force when it is in an electric field. There are only two kinds of charge: positive (+) and negative (−).

How Charges Interact

The force between two charges is described by Coulomb’s Law:

\$F = k \frac{q1 q2}{r^2}\$

Here, \$F\$ is the force, \$q1\$ and \$q2\$ are the charges, \$r\$ is the distance between them, and \$k\$ is Coulomb’s constant. From this formula we learn:

  • Positive charges repel other positive charges. ⚡

  • Negative charges repel other negative charges. ⚡

  • Positive and negative charges attract each other. 💫

Analogies to Understand Attraction and Repulsion

Think of charges like people at a party:

  1. Two people who agree on everything (both positive or both negative) tend to push away from each other.

  2. Two people who disagree (positive and negative) are drawn together, just like magnets.

Quick Reference Table

Charge 1Charge 2Interaction
Positive (+)Positive (+)Repel
Negative (−)Negative (−)Repel
Positive (+)Negative (−)Attract
Negative (−)Positive (+)Attract

Key Takeaway

Like charges repel, unlike charges attract. This simple rule is the foundation of all electrostatic phenomena and will help you solve many physics problems.