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ELECTRICITY
A FLASH OF LIGHTNING leaping through the sky during a
thunderstorm is one of the most visible signs of electricity. At almost
all other times, electricity is invisible, but hard at work for us. Electricity
is a form of energy. It consists of electrons—tiny particles that come from
atoms. Each electron carries a tiny electric charge, which is an amount of
electricity. When you switch on a light, billions of electrons move back and
forth inside the bulb many times each second. Cables hidden in walls and
ceilings carry electricity around houses and factories,
providing energy at the flick of a switch. Electricity also provides
portable power. Batteries produce electricity from chemicals, and
solar cells provide electricity from the energy in sunlight. Lamps,
motors, and dozens of other machines use electricity as their
source of power. Electricity also provides signals that make
telephones, radios, televisions, and computers work.CURRENT ELECTRICITY
Electricity comes in two forms: electricity that
flows, and static electricity, which does not move.
Flowing electricity is called current electricity.
Billions of electrons flow along a wire to
give an electric current. The
electricity moves from a
source such as a battery or
power station to a machine.
It then returns to the source
along another wire. The flow of
Some power electric current is measured in amperes (A).
stations generate
electricity by burning
coal and oil. Other
stations are powered
by nuclear energy.
A transformer
boosts the
voltage (force) of
the electricity to
many thousands
of volts.Tall pylons
support long cables
that carry the
electricity safely
above the ground to
all parts of an area.Electricity flows into
homes through cables that
run either underground or
above street level on poles.STATIC ELECTRICITY
There are two types of electric charge,
positive (+) and negative (–). Objects
usually contain equal numbers of both
charges so they cancel each other out.
Rubbing amber (fossilized resin from
trees) against wool or fur makes it
pick up extra electrons, which carry a
negative charge. This charge is called
static electricity. It produces an electric
force that makes light objects, such as
hair and feathers, cling to the amber.Wires connect
battery and bulb
to form a circuit.Bulb in bulb holderMost plastics
are insulators. ELECTRIC CIRCUITS
Electric current needs a
continuous loop of wire to
flow around. This is called a circuit.
If the circuit is broken, the electricity
can no longer flow.Battery pushes
electric current
around the circuit.Power stations
produce
alternating
current, which
flows first in one
direction and
then the other.Another
transformer
reduces the voltage
of the electricity
to levels suitable
for domestic
appliances.Electrons flow
through copper
conductor.Batteries
produce direct
current, which
flows one way
around a circuit.SUPERCONDUCTORS
Ordinarily conductors, while
letting most electricity flow
through them, also resist it
to some extent. So a certain
amount of electricity is lost.
However, some materials
lose their resistance when
very cold. They become
superconductors.A superconductor can produce a strong
magnetic field that makes a small
magnet hover above it.CONDUCTORS AND INSULATORS
Electricity flows only through materials
called conductors. These include copper
and many other metals. Conductors can
carry electricity because their own
electrons are free to move. Other
substances, called insulators, do
not allow electricity to flow
through them. This
is because their
electrons are held
tightly inside
their atoms.