Attraction & Repulsion

Rubbing a polythene strip on wool causes some of the outer electrons in the wool to move over to the polythene strip. As the polythene gains electrons it becomes negatively charged. The wool looses electrons and is left with a net positive charge (more protons to electrons).

Only the negative electrons move. The positive protons remained fixed in the atoms nucleus.

Rubbing materials to generate charge only works for insulated objects. Conductors direct the charge flow to earth.

When two electrically charged bodies are brought together they exert a force on each other. Electrically charged objects may attract or repel each other or attract small uncharged objects place near them.

 

Example

Balloon

A balloon can be made to stick to a wall by using the principles of electrostatics.

 

 

When a balloon is rubbed against clothes the negative electrons from the clothes get transferred to the balloon making the balloon negatively charged. When the balloon is placed near a wall or ceiling (a neutral object) it stays there and doesn’t fall. This is because the negative charge of the balloon repels some of the electrons in the wall or ceiling away from the surface. This results in an overall positively charged surface causing the negatively charged balloon to be attracted (remember opposite charges attract).

The separated charges in the wall or ceiling are called INDUCED charges.

---