Lightning and Thunder
Activity 4
Rub your foot on a
carpet floor and touch a door knob. What do you feel? Do you feel the shock in
your hand? Why does this happen?
Answer: Getting a shock from a doorknob after rubbing your foot on a
carpet floor, results from discharge. Discharge occurs when electrons onthe
hand are quickly pulled to the positively charged doorknob. This movement of
electrons,which is felt as a shock, causes the body to lose negative charge.
Getting a shock from a door knob
after rubbing your foot on a carpet floor, results from discharge. Discharge
occurs when electrons on the hand are quickly pulled to the positively charged
doorknob. This movement of electrons, which is felt as a shock, causes the body
to lose negative charge. Electric discharge takes place in a medium, mostly
gases. Lightning is another example of discharge that takes place in clouds.
Lightning is produced by discharge
of electricity from cloud to cloud or from cloud to ground. During thunderstorm
air is moving upward rapidly. This air which moves rapidly, carries small ice
crystals upward. At the same time, small water drops move downward. When they
collide, ice crystals become positively charged and move upward and the water
drops become negatively charged and move downward. So the upper part of the
cloud is positively charged and the lower part of the cloud is negatively
charged. When they come into contact, electrons in the water drops are
attracted by the positive charges in the ice crystals. Thus, electricity is
generated and lightning is seen.
Sometimes the lower part of the
cloud which is negatively charged comes into contact with the positive charges
accumulated near the mountains, trees and even people on the earth. This
discharge produces lot of heat and sparks that results in what we see as
lightning. Huge quantities of electricity are discharged in lightning flashes
and temperatures of over 30,000°C or more can be reached. This extreme heating
causes the air to expand explosively fast and then they contract. This
expansion and contraction create a shock wave that turns into a booming sound
wave, known as thunder.
Lightning's
extreme heat will vaporize the water inside a tree, creating steam that may
burn out the tree.
Sometimes lightning may be seen
before the thunder is heard. This is because the distance between the clouds
and the surface is very long and the speed of light is more than the speed of
sound.
During lightning and
thunder, we should avoid standing in ground or open spaces. You should make
yourself as small as possible bysquating. It is however safe to stay inside a
car because the car acts as a shield and protects us from the electric field
generated by the storm.
1. Earthing
A safety measure devised to prevent
people from getting shocked if the insulation inside electrical devices fails
is called earthing. Electrical earthing can be defined as the process of
transferring the discharge of electrical energy directly to the earth with the
help of low-resistance wire.
We get electrical energy from
different sources. Battery is one such source. We use it in wall clocks, cell
phones etc. For the working of refrigerators, air conditioners, washing
machines, televisions, laptops and water heaters we use domestic power supply.
Usually an electric appliance such as a heater, an iron box, etc. are fitted
with three wires namely live, neutral and earth. The earth wire is connected to
the metallic body of the appliance. This is done to avoid accidental shock.
Suppose due to some defect, the
insulation of the live wire inside an electric iron is burnt then the live wire
may touch the metallic body of the iron. If the earth wire is properly
connected to the metallic body, current will pass into the earth through earth
wire and it will protect us from electric shock. The earth, being a good
conductor of electricity, acts as a convenient path for the flow of electric
current that leaks out from the insulation.
2. Lightning Arresters
Lightning arrestor is a device used
to protect buildings from the effects of lightning. Lightning conductor
consists of a metallic lightning rod (in the form of spikes) that remains in
air at the top of the building. Major portion of the metal rod and copper cable
are installed in the walls during its construction. The other end of the rod is
placed deep into the soil. When lightning falls, it is attracted by the
metallic rods at the top of the building. The rod provides easy route for the
transfer of electric charge to the ground. In the absence of lightning
arrestors, lightning will fall on the building and the building will be damaged.
Related Topics
Privacy Policy, Terms and Conditions, DMCA Policy and Compliant
Copyright © 2018-2023 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.