What Is Static Electricity?
Static electricity is a build-up of electric charge on an object's surface. Unlike current electricity, the charge does not flow — it stays put (static).
Charging by Friction
When two materials are rubbed together, electrons transfer from one to the other.
- The material that gains electrons → becomes negatively charged (−)
- The material that loses electrons → becomes positively charged (+)
Common examples:
- Balloon rubbed on hair — balloon becomes negative; hair becomes positive
- Walking on carpet then touching a door handle → small shock
- Combing dry hair causes it to stand up (like charges repel)
Attraction and Repulsion
Like charges repel; unlike charges attract.
| Situation | Outcome |
|---|---|
| Two negative charges near each other | Repel |
| Two positive charges near each other | Repel |
| Positive and negative charges near each other | Attract |
A charged object will also attract a neutral (uncharged) object — it induces a temporary charge separation in the neutral object.
Lightning
Storm clouds build up large static charges through collisions between ice and water droplets. When the charge difference between the cloud and ground becomes large enough, electrons jump across the air gap — lightning.
Lightning rods (conductors on tall buildings) provide a safe path for the charge to flow to the ground.
Why does a balloon stick to the wall after rubbing it on hair?
Rubbing transfers electrons to the balloon — it becomes negatively charged. The wall is neutral but the balloon repels electrons near the surface, leaving a positive region. The negatively charged balloon is attracted to this positive region on the wall.
Real world: photocopier drum
A photocopier drum is given a uniform positive electrostatic charge. A laser then removes charge from areas matching the white parts of the document. Negatively charged black toner powder is attracted only to the remaining positive areas, printing an exact copy. Static electricity enables every laser printer and photocopier.
Real world: lightning and lightning rods
A thundercloud builds up millions of volts of static charge through collisions between ice crystals. When the electric field becomes strong enough, electrons jump from cloud to ground as a lightning bolt. A lightning rod provides a low-resistance conductor that safely channels this discharge to ground, protecting buildings.
Real world: spray painting and powder coating
In electrostatic spray painting, the paint droplets are given a negative charge while the metal object is earthed (positive). The charged droplets are strongly attracted to the object and spread evenly, even around curved surfaces. This reduces paint waste and gives a more uniform coat than conventional spraying.
Practice Problems
A plastic rod is rubbed with a cloth. The rod becomes negatively charged. What charge does the cloth have?
Show answer
Give one safety use and one hazard of static electricity.