Page 150 - Science Class 08

begins to condense to droplets of liquid water. form of lightning. Lightning, some mes,

This condensa on releases heat and warms the become very devasta ng it falls on a building.
air further, giving added impetus to the rising air Lightning Conductor
currents. The condensed moisture starts to fall. Franklin said that the wire cord can be used to

As these drops of water fall through the mass protect the buildings from lightning strike. He
of rapidly rising air, fric on with the air tears suggested the use of metallic wires or rods in
some of the drops apart into spray. buildings to conduct the charge to the earth to
In this process, electrical charges are gene- save the buildings. Thus, the use of lightning
rated. The water drops falling to the lower conductors come into being.
levels of the clouds have a nega ve charge, the A lightning conductor is a metal rod fi ed on
five spray that rises to the upper levels, a the roof of tall buildings. The top of it is pointed

posi ve one. and the lower end is connected by wire to the
A cloud may build up a posi ve charge or a ground. The nega ve charges on the underside
nega ve one or different charges. Some mes, of clouds a ract the posi ve charges from the
these clouds will accumulate charges un l ground. A stream of these posi ve charges flow
sparks jump from one cloud to another of up to the cloud through this conductor. They

opposite charge and the charges are neutra- cancel out some of the nega ve charges on the
lised. Such a spark or chain of sparks is called clouds. This may prevent lightning from striking.
lightning. If the lightning does strikes, the electricity is
conducted through the metallic conductor to
Some mes, a huge amount of charge flings
the earth.
towards the earth to get neutralised in the

Static electricity : Electricity at rest
Atom : Smallest particle of matter

Charged body : Gaining or losing electrons by the body
Electroscope : A simple instrument which is used to find whether an object is
charged or not
Conductor : An object that allows electricity to pass through it

Insulator : An object that does not allow electricity to pass through it
Electric current : Electricity in motion
Lightning : Transfer of huge amount of charge from the clouds

Lightning conductor : A simple instrument that protects structure from lightning

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i The word electricity comes from the Greek word electron which means amber.
i When electric charges are produced by rubbing one material upon another, these charges are
called static electricity.

150 Science-8