Textbook Solutions: Wind and Strom | Class 7 Oxford Science: Chapter Notes, Worksheets & Tests PDF Download

A. Choose the correct option

1.
Ans: (b)

2.
Ans: (d)

3.
Ans: (d)

4.
Ans: (b)

5.
Ans: (d)

B. Fill in the blanks with the correct words.

1.
Ans: A strip of paper will be lifted if we blow air in a horizontal direction over it.

2.
Ans: Roofs can be blown off because moving air creates a low pressure.

3.
Ans: A wind vane points in the direction of the wind.

4.
Ans: Cyclones form in the oceans near the equator.

5.
Ans: Cyclones become stronger if they pass over warm water of the ocean.

C. Match the Following.

1.
Ans:

D. Give reason for the following.

1.
Ans: A heated metal crumples up when held under cold running water because of the sudden and rapid change in temperature. This rapid cooling causes the metal to contract quickly, which can result in the metal crumpling or warping.

2.
Ans: Roofs can be blown off during a strong wind because of the difference in air pressure. As wind blows over a rooftop, it moves faster and thus, creates a region of lower pressure over the rooftop. Inside the house, under the roof, the air pressure is higher. This imbalance in pressure can lead to the roof being lifted and blown off if it is not adequately secured.

3.
Ans: The rear end of the wind vane has a larger surface area than the front end to catch the wind. The wind pushes the larger surface area of the tail, causing the vane to rotate and point the arrow (smaller end) in the direction the wind is blowing from.

4.
Ans: Storms can be destructive due to their high-speed winds and heavy rainfall. These can cause large-scale damage to buildings, trees, and other structures. In severe cases, storms can result in flooding, landslides, and loss of life.

E. Answer the following questions.

1.
Ans: Storms are caused by atmospheric disturbances and are accompanied by very strong, high-speed winds. They are often formed over warm ocean waters. The warm air over the oceans rises, leaving behind a region of low pressure. This causes colder air from the surroundings to rush in, spiraling inward due to the Earth's rotation.

2.
Ans: Effects of severe storm:
(a) On land - Severe storms can cause a significant amount of damage. Trees can be uprooted, electric poles and hoardings can fall, and buildings can be damaged or completely destroyed. There can also be considerable flooding caused by heavy rain.
(b) At sea - Cyclonic storms produce very high waves and increase the sea level much above the normal sea level. This makes it dangerous for fishermen to go out to sea.

3.
Ans: Construction and working:
(a) Wind vane - A wind vane is an instrument used to find the direction of the wind. It can be made in any shape, but the tail should be larger than the tip. The wind pushes the larger surface area of the tail, causing the vane to rotate and point the arrow (smaller end) in the direction the wind is blowing from.
(b) Anemometer - An anemometer is used to measure wind speed. The most common type is a cup anemometer. When the wind blows, the cups rotate. The speed of rotation can be measured to calculate the wind speed.

4.
Ans: The dangers of a storm to people and property include physical harm or death, destruction of buildings, flooding, and disruption of essential services like electricity and water supply.

5.
Ans: Safety measures during a storm warning include listening to news updates, stocking up on food and water, securing loose objects, and staying indoors. If evacuation is required, one should follow the instructions from authorities. One should also avoid touching anything that may be exposed to electricity lines.