Static Electricity

Junior Science

Learning Intentions

• be able to produce static electricity.

• be able to observe the effects of static electricity.

• Be able to recognize and define the terms attract and repel as they relate to static electricity.

• Explain how a Van der Graff Generator Works

• Understand the dangers of static electricity in relation to electrical appliances.

What is Static Electricity?

• A stationary electrical charge that is built up on the surface of a material

Where do charges come from?

Matter is made up of atoms.

Proton (positive charge)

neutron (neutral)

electron (negative charge)

atom

++

+

–

––

+

–

nucleus

Two kinds of charges

• After being rubbed, a plastic ruler can attract paper scraps.

Ruler carries electric charge.

It exerts electric force on paper.This charging method is called charging by friction.The interaction between static electric charges is called electrostatics.

Where do charges come from?

If electrons = protons neutral

If electrons > protons gaining electrons

negative charge

If electrons < protons losing electrons

positive charge

Electro-negativity

Relative

electro-negativity

ranking for some

common materials

from

electron donating

materials (+, glass) to

electron accepting

materials (-, teflon)

• Glass

• Human Hair

• Nylon

• Silk

• Fur

• Aluminum

• Paper

• Cotton

• Copper

• Rubber

• PVC

• Teflon

+ + + + ++ + + ++ + ++ ++

-- -- - -- - - -- - - - -

Where do charges come from?

Rubbing materials does NOT create

electric charges. It just transfers

electrons from one material to the

other.

Where do charges come from?

When a balloon rubs a piece of Fur...

electrons are pulled from the wool to the balloon.

+

+

+

+

+

–––––

Fur

Where do charges come from?When a balloon rubs a piece of Fur...

–Electrons are pulled from the wool to the balloon.

The balloon has more electronsthan usual.

+

+

+

+

+

–––––

Fur

Where do charges come from?When a balloon rubs a piece of Fur...

– Electrons are pulled from the

wool to the balloon.

The balloon has more electrons than

usual.

+

+

+

+

+

–––––

The balloon: – charged

The wool: + charged

Fur

Insulators and Conductors

Insulators are materials that do NOT allow electrons to flow through them easily.

Insulators can be easily charged by

friction as the extra electrons gained

CANNOT easily escape.

Insulators and Conductors

Conductors are materials that allow electrons to flow through them easily.

Conductors CANNOT

be easily charged by

friction as the extra

electrons gained can

easily escape.

Static Discharge

Human body can not feel less than

2,000 volts of static discharge.

Static charge built up by scuffing shoes on a carpet can exceed 20,000 volts?

The carpet has an excess of electrons

Static Discharge

As the man walks he picks up electric Charge.

Static Discharge

On shaking hands, the electric charge is discharged giving her a shock.

Static Discharge

Van de Graff Generator

• An electrostatic generator which uses a moving belt to accumulate electric charge on a hollow metal globe on the top of an insulated column.

• creating very high electric potentials.

• It produces very high voltage direct current electricity at low current levels.

Grounding

An object is grounded when it is connected to the earth through a connecting wire.

What is grounding?

If a charged conductor is grounded, it will become neutral.

++++

+

When we touch a metal ball of positive charge...

electrons flow from the earth to the metal ball to neutralize the metal ball.

Metal ball becomes neutral.

How does grounding occur?

Similarly, if the metal ball is of negative charge...

–

–––

– extra electrons flow from the metal ball to the earth and the ball becomes neutral.

How does grounding occur?

Earthing

• Earthing is used to protect you from an electric shock. It does this by providing a path (a protective conductor) for a fault current to flow to earth.

• It also causes the protective device (either a circuit-breaker or fuse) to switch off the electric current to the circuit that has the fault.

Summary

• Static electricity is a stationary electrical charge that is built up on the surface of a material.

• Rubbing material together causes a transfer of electrons and creates static charge.

• Objects gain electrons to becomes negatively charged.

• Objects loses electrons and become positively charged.

• Like charges repel each other and unlike charges attract.

• Grounding is when a charged object loses its charge to the earth. This occurs when a charged object is connected to the ground by a conductor.