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Static electricity

Electricity and magnetism · level 3, lesson 1 of 6

A question to start

Rub a balloon on your hair, then hold it against a wall. It stays there, as if glued. What has the rubbing done?

The idea

Everything is made of tiny atoms. Each atom has a centre with positive charge, and much lighter electrons round it with negative charge. Usually the two balance, so things have no overall charge.

Rubbing two materials together can move some electrons from one to the other.

  • The balloon picks up extra electrons, so it becomes negatively charged.
  • Your hair loses electrons, so it becomes positively charged.

The charge stays where it is on the balloon, because rubber is an insulator. Charge that stays put is called static electricity. "Static" means "not moving".

−−−−−− ++++ balloon: extra electronshair: lost electrons

Worked examples

1. A crackling jumper. Pull off a wool jumper on a dry day and you hear crackles: charge built up by rubbing is jumping across in tiny sparks.

2. A comb and paper. Comb dry hair, then hold the comb over tiny bits of paper. They jump up to it.

3. Which way. When a balloon is rubbed on hair, electrons move from the hair to the balloon. The balloon ends up negative, the hair positive.

Try it

  1. What are the tiny negatively charged parts of atoms called?
  2. What does rubbing do to the electrons?
  3. A balloon has gained electrons. What is its charge?
  4. Why does the charge stay on a balloon instead of flowing away?
Answers
  1. Electrons.
  2. It moves some of them from one material to the other.
  3. Negative.
  4. Rubber is an insulator, so the charge cannot flow through it.

Common mistake

"Rubbing makes new charge." Rubbing only moves electrons from one thing to another. One gets just as much positive charge as the other gets negative.

Where it leads