6.3 Electrostatics

Static electricity is the build-up of electric charge on an object, which is usually an insulator (a material that does not let charge flow easily, like plastic or rubber).

This charge builds up when two insulating materials are rubbed together. Electrons (which are negatively charged) are transferred from one material to the other.

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

Like charges (positive and positive, or negative and negative) will repel each other. Opposite charges (positive and negative) will attract each other.

Example: Rubbing a balloon on your hair transfers electrons from your hair to the balloon. Your hair becomes positive and the balloon becomes negative, so they attract.

When a large static charge builds up, it can discharge as a spark. This is the charge jumping through the air to a conductor or to the earth.

This spark can be dangerous if it happens near flammable gases or liquids (like at a petrol station), as it can cause an explosion.

Lightning is a massive-scale example of a static discharge between a cloud and the ground.

To prevent this, we use earthing (or "grounding"). An object at risk of charge build-up (like a fuel tanker) is connected by a conductor (a wire) to the ground. This provides a safe path for any charge to flow away, preventing a spark.

An electric field is the region around a charged object where another charged object will experience a (non-contact) force.

We can draw electric field lines to show the direction and strength of the field.

• The lines show the direction a positive charge would be pushed.
• Lines point away from positive charges and towards negative charges.
• The closer the lines are, the stronger the field.

Source: Wikimedia Commons