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A lightning strike demonstrates the incredible energy of

electricity. This intense flash of heat and light is created

naturally by static electricity. We use this same electric

force to provide a clean, controllable power supply to

our homes, farms, factories, and cities.

HOW DOES INDUCTION WORK?

When the comb is brought close to

the paper, the negative charge

on the comb repels electrons in

the paper to the side farthest away

from the comb. This creates a

positive charge (fewer electrons) on

the side of the paper facing the comb.

Positive and negative attract,

so the paper is pulled towards the comb.

2 USING ELECTROSTATICS

By making the car body

and the paint sprayer

oppositely charged, paint

drops are attracted into

all the bumps and

hollows of the

surface to

be painted.

Electric induction is the process by which a charged object can

charge another object without touching it. A charged

nylon comb, for example, will attract scraps of paper,

even though the scraps are not charged themselves.

WHAT IS ELECTRICITY?

The electrons and protons inside every atom carry a

property called an electric charge. Electrons have a

negative charge and protons a positive charge. These

charges either attract or repel each other. Unlike

(opposite) charges attract, and like (the same) charges

repel. The force they do this with is called electricity.

HOW MANY FORMS OF ELECTRICITY ARE THERE?

Electricity comes in two forms – as electric current

when electric charges flow along wires in a circuit,

and as static electricity, when electric charges do not

move. Normally, most materials are neutral (have no

charge). But if a material gains or loses large numbers

of electrons it becomes charged with static electricity.

HOW DO MATERIALS BECOME CHARGED?

Materials can become charged with static electricity

by. INDUCTION or by friction. When two materials

rub together, friction transfers electrons from one to

the other. This gives one material a negative charge,

and the other a positive charge. A nylon comb gains a

negative charge when it is pulled through hair.

4 GOLD LEAF ELECTROSCOPE

Electric charge can be measured by an electroscope. One of the simplest

is a gold-leaf electroscope. A charged object held near the cap repels

like charges to the far end of a metal rod, onto a thin sheet of gold. The

charges on the gold leaf and the rod repel each other, and the leaf rises.

The amount by which it rises can be measured against a notched scale.

ELECTROSTATIC INDUCTION

ELECTRIC LIGHTNING 3

The build-up of electric charge

in a thunder cloud creates an

opposite charge in the ground.

Eventually, a gigantic electric

spark leaps between the two

charges in a spectacular release

of energy.

4 PLASMA GLOBE

A charged metal ball causes electrons to separate from gas atoms inside

a glass sphere. The gas gives out light as electrons flow through it.

Electricity

Lightning stroke

between cloud

and ground may

be up to14 km

(9 miles) long

Lightning flash

heats the

surrounding air

to 30,000°C

(54,000°F)

Charged

nylon comb

attracts

paper scraps

Gold leaf

Scale

Rod

Cap

FIND OUT MORE. Atoms 157 • Circuits 184–185 • Forces 164 • Motion 165

182 Science and Technology

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electricity