NCERT 7th Class (CBSE) Science: Winds, Storms and Cyclones

Question: What is the climatic condition formed by lightning and thunder mostly accompanied by rain called?

Answer: A thunderstorm is a turbulent weather condition formed by lightning and thunder. Thunderstorms are usually accompanied by strong winds and heavy rains.

Question: What is a low-pressure area surrounded by a high pressure region of swirling air called?

Answer: A low-pressure area surrounded by a high pressure region of swirling air called a cyclone.

Question: Hot air rises up and cool air sinks down. Explain why.

Answer: The flow of air in the atmosphere of the Earth is called wind. When air on the surface of the Earth is heated by the sun, it expands and rises up creating a low-pressure region below. Air from the nearby high-pressure regions flows into these low-pressure regions and causes wind. The hot air that rises up cools and sinks down. This continues and a cycle of airflow is formed, which is called the wind current.

Question: How are thunderstorms formed?

Answer: When the air near the surface of the Earth gets heated by the sun, it rises up. The hot rising air carries moisture. As this air reaches the cooler regions of the atmosphere, the water wapour in the air gets condensed to form tiny droplets of water which join together to from clouds. When clouds become heavy with water droplets, these water droplets fall as rain. As they fall, they collide with each other and also with the air rising up. This friction between the droplets and the air particles charges the clouds. The charging of clouds causes electrical discharge between a cloud and the ground. This discharge of electricity through the atmosphere of the Earth causes huge sparks known as lightning. Due to lightning, the air in the path of discharge of electricity is heated up, causing the air in this region to expand suddenly with huge sound called thunder.

Question: Write the precautions to be taken during tornadoes.

Answer: A tornado funnel can engulf objects from the surface of the Earth (due to low pressure inside) and throw these back, causing destruction. Some necessary precautions to be taken during tornadoes are given below:

1. Avoid opening windows and doors of houses. Occupy the ground floor and small rooms in your house.
2. If you are outside or travelling in a vehicle, get out of it quickly and protect yourself by lying close to the ground by keeping your fingers interlocked, closing the ear and the neck.

Question: Explain the formation of wind and wind currents with the help of a diagram.

Answer: Wind flowing over a region reduces the air pressure in that particular region. The more the speed of the wind, the lower will be the pressure. Wind currents are formed due to the uneven heating of the Earth’s surface between the equator and the poles. The equatorial regions receive more sunlight compared to the polar regions. Therefore, the air near the Earth’s surface in the equatorial regions gets heated and rises up. This process creates low-pressure regions. Cold air from the high-pressure regions on ether side of the equator, up to the latitude of 30°, flows into the law-pressure regions near the equator.