Physics Topics such as mechanics, thermodynamics, and electromagnetism are fundamental to many other scientific fields.
What Causes a Thunderstorm?
Many times during a storm which brings heavy rain, we also hear loud sound called ‘thunder’ coming from the clouds and see the bright flashes of ‘lightning’ as well. A storm with thunder and lightning is called thunderstorm.
A thunderstorm is accompanied by heavy rains or hail (The pellets of frozen rain or ice falling in showers from clouds is called hail). Thunderstorm is produced by the dark clouds which form at fairly low altitude in the atmosphere.
Thunderstorm is called ‘garajwala toofan’ in Hindi. Thunderstorms develop in hot and humid tropical areas (like India) very frequently. This is because thS heat of tropical area warms up the air and makes it rise up, whereas humidity provides the water vapour for the formation of clouds. A thunderstorm is formed as follows.
The sun heats the surface of earth. The hot surface of earth warms the air in contact with it. The warm air (being lighter) rises up creating a low pressure area. And cool air rushes in to take its place in the form of strong winds. As the warm air rises, it transfers heat to the upper levels of atmosphere and begins to cool.
The water vapour present in the rising air cool and condense to form a cloud. The cloud grows upwards into areas where the temperature is close to the freezing point of water (0°C). Some of the water vapour of cloud forms tiny water droplets and some of it turns into ice particles. The water droplets are carried upwards in the cloud (by convection currents) but the ice particles drift downwards.
The friction between fast rising ‘water droplets’ in the cloud and falling ‘ice particles’ produces opposite electric charges on them (the water droplets getting positive electric charge and ice particles acquiring negative electric charge). Due to this, the top of cloud becomes positively charged and the bottom of cloud becomes negatively charged.
When a large amount of opposite electric charges build up in the cloud, a tremendous amount of electric current passes through the air in the cloud which produces a big electric spark within the cloud. This electric spark is the lightning (see Figure). The spark of lightning heats the nearby air too much. This extremely hot air expands explosively causing a loud sound called thunder.
When electric charges from the bottom of the electrically charged cloud flow down through the air to the ground, then we see the flash of lightning coming towards the earth. The big water drops in the thundercloud fall to the earth as heavy rain (or hail). In this way, a thunderstorm brings strong winds, thunder, lightning and heavy rains (or hail).
Precautions To be Taken During a Thunderstorm
A thunderstorm is always accompanied by lightning. Lightning is a giant electric spark. When lightning strikes the earth, it can kill people. It also damages buildings. We should take the following precautions during a thunderstorm to protect ourselves from lightning.
- We should not sit near a window during lightning. Open garages, storage sheds and metal sheds are also not safe places to take shelter during lightning.
- We should not take shelter under an umbrella with a metallic end during lightning. This is because metallic end of umbrella may act as a conductor for lightning and harm us.
- We should not take shelter under an isolated and tall tree. This is because an isolated tall tree is more likely to be hit by lightning due to its nearness to the clouds. We should take shelter under a small tree. We should, however, not lie on the ground during lightning.
- A car (or a bus) is a safe place to take shelter during lightning (because its metal body can conduct lightning to earth safely, without harming us).
- If we are in water (as in a swimming pool or on a beach) when the thunderstorm begins and lightning takes place, we should get out of water and go inside a building.
Before we describe a cyclone, it is necessary to know what supplies energy to form and sustain it. The energy required to form and sustain a cyclone comes from the heat of condensation of water vapour present in moist air rising from the surface of hot sea water.
This will become clear from the following discussion. We know that water absorbs heat and changes into water vapour. This absorbed heat gets stored in water vapour. Now, when water vapour gets cooled and condenses to form liquid water, it releases the stored heat. This is called the heat of condensation of water vapour.
A cyclone is powered by the heat of condensation of water vapour present in the warm, high moisture air which rises from the warm sea surface and condenses at high altitudes to form clouds. The sea-water becomes warm because it is heated by the sun’s heat rays. It is the warm sea-water which provides heat continuously for the evaporation of water to form water vapour.