8. Static Electricity

• Electric charge in clouds is attracted towards tall and pointed objects.
• An umbrella has a metal rod with a pointed tip. Metal is a good conductor of electricity.
• If lightning strikes the umbrella, the charge passes through the person’s body into the ground.
• This can cause a severe shock or even death.

So it is not safe to go out with an umbrella during lightning.

• Stay inside a building with a lightning conductor.
• Do not stand under a tree, near an electric pole or in an open field.
• Keep away from water.
• Do not hold metal objects like an umbrella.
• If caught outside, sit low on the ground with feet together.
• Switch off and unplug electrical appliances.

Every object has equal positive and negative charges. So it is neutral. An object gets charged when negative charges move from one object to another. This happens in three ways:

• By friction: When two objects are rubbed, negative charges move from one to the other. Example: a comb rubbed on dry hair.
• By contact: When a charged object touches an uncharged object, some charge passes to it.
• By induction: When a charged object is brought near an uncharged object, opposite charge appears on its nearer side.

The lower end of the copper strip is joined to a cast iron plate. A pit is dug in the ground. It is filled with coal and salt. The iron plate is kept in this pit. Water is poured into the pit. Coal and salt keep the soil moist. So the electric charge spreads quickly into the ground.

An open field has no tall objects. So lightning may strike the farmer. An iron staff stuck in the ground is taller than the farmer. Iron is a good conductor. So the electric charge passes through the staff into the ground. Thus, the iron staff works like a lightning conductor and protects the farmer.

Lightning occurs only when a very large amount of charge collects in the clouds. This happens only in special thunderclouds. On most rainy days, the clouds do not have so much charge. So lightning is not seen every day.

• It is produced by friction, only at the place of rubbing.
• It stays at one place on the object. It does not flow.
• It remains for a short time only.
• It is quickly lost in moist air.
• Like charges repel and unlike charges attract each other.
• A charged object attracts small pieces of paper.
• It can be detected by an electroscope.

Damage caused by lightning:

• People and animals may get burnt or die.
• Trees may split or catch fire.
• Buildings may get damaged.
• Electric lines and appliances may burn out.

Creating awareness:

• Put up posters on dos and don’ts during lightning.
• Arrange talks and street plays for farmers before the monsoon.
• Show the working of a lightning conductor with a model.
• Tell people about the ‘Damini’ mobile app that gives lightning warnings.

1. Take a dry glass jar with a cardboard lid.
2. Pass a copper wire through the lid. Bend its lower end into a hook.
3. Hang two thin strips of aluminium foil on the hook.
4. Fix a small ball of foil on the upper end of the wire.
5. Rub an object and bring it near the foil ball. If the strips move apart, the object is charged.

Observation: A plastic comb, balloon, glass rod and plastic ruler get charged when rubbed. A steel spoon and copper strip held in the hand do not get charged.