Electric Charge and Static Electricity

Atoms and charge

Everything is made of atoms. Atoms contain three kinds of particles:

A normal atom has the same number of protons and electrons, so the charges cancel. The atom is neutral.

Protons are locked in the nucleus. Electrons are the ones that can move from one object to another.

Making static charge

When you rub two different materials together, electrons are transferred from one to the other.

• The object that gains electrons becomes negatively charged.
• The object that loses electrons becomes positively charged.

The electrostatic force

Charged objects push or pull each other without touching. This is the electrostatic force, a non-contact force.

• Like charges repel: + and +, or − and −.
• Unlike charges attract: + and −.
• A charged object can also attract a neutral object. The balloon pushes the wall's electrons slightly away, leaving the nearby surface a bit positive. Then the negative balloon is attracted to it.

The force is stronger when the charges are bigger and when the objects are closer.

Conductors and insulators

• Conductors let electrons flow through them easily: metals (copper, aluminium), graphite, salty water, the human body.
• Insulators do not let electrons flow: plastic, rubber, glass, wood, dry air.

Static charge builds up on insulators, because the charge cannot flow away. If you rub a metal rod while holding it, the charge flows through you into the ground. This is called earthing.

Static electricity in real life

• Shocks: walking on carpet charges you up. Touching a metal door handle lets the charge jump. Zap.
• Lightning: ice and water bumping inside storm clouds separate huge amounts of charge. When it gets big enough, it jumps to the ground as a giant spark.
• Fuel tankers are earthed while refuelling, so a spark cannot ignite the fuel.
• Useful: photocopiers, laser printers and spray painting cars all use static charge.

Quick summary

• Atoms contain positive protons, negative electrons and neutral neutrons.
• Only electrons move between objects.
• Gain electrons: negative. Lose electrons: positive.
• Like charges repel. Unlike charges attract. Closer means stronger.
• Conductors let charge flow. Insulators do not, so static builds up on them.
• Lightning and static shocks are sudden flows of built-up charge.

Quiz