NCERT Exemplar Problems Class 7 Science – Wind, Storm and Cyclone

Question 1:
A fire alarm usually detects smoke in case of fire. Where should such an alarm be placed in a room?
(a) Near the door
(b) On the floor
(c) On any wall
(d) On the ceiling
Answer:
(d) In case of fire, the air above the fire becomes hotter and rises up. So, the alarm should be laced on the ceiling in a room, it can detect the smoke rising up.

Question 2:
Four schematic diagrams are shown below to depict the direction of sea breeze. Which of them gives the correct direction?

Answer:
(c) In summer, during the day the land becomes warm and the air over the land gets heated and rises. This causes the cooler air blow from the sea towards the land.
The warm air from the land moves towards the sea to complete the cycle. The air from the sea, moving towards the land is called sea breeze.

Question 3:
Figure shows a child blowing air with a straw near the opening of another straw which has its other end in a soft drink bottle. It was observed that the level of the soft drink in the straw rises up as soon as air is blown over its open end. Which one of the following best explains the reason for rise in level of the drink?

(a) Blowing of air decreases pressure over the opening of the straw
(b) The straw of the soft drink bottle collapses when air is blown over its open end
(c) Blowing of air warms up the air inside the straw
(d) Blowing of air increases the pressure on the surface of soft drink in the bottle
Answer:
(a) Blowing of air decreases the pressure over the opening of the straw due to which the level of the soft drink in the straw rises up.

Question 4:
Following are precautions, one must take in case a storm is accompanied by lightning.
(i) Do not take shelter under tree.
(ii) Do not take shelter under an umbrella with a metallic end.
(iii)Do not take shelter in open garages, storage sheds, etc.
(iv) Do not take shelter in a bus in the open.
Which one of these is not correct?
(a) (i)
(b) (ii)
(c) (iii)
(d) (iv)
Answer:
(d) Because a car or a bus is a safe place to take shelter in such a situation.

Question 5:

Which of the following place is most likely to be affected by a cyclone?
(a) Mumbai
(b) Puri
(c) Goa
(d) Porbandar
Answer:
(b) Puri is most likely to be affected by a cyclone because this city lies near the coastal area.

Question 6:
A curtain is hanging at the entrance of a room. A long corridor runs at right angles to the door, that is parallel to the curtain. If a strong wind blows along the corridor, the curtain will
(i) get pushed inside the room
(ii) get pushed outside the room
(iii) get collected towards one end/ swirled
(iv) remain unaffected
Answer:
(b) if a strong wind blows along the corridor, then the air pressure there increases and the curtain gets pushed outside the room.

Very Short Answer Type Questions

Question 7:
Why is Chandigarh unlikely to be affected by a cyclone?
Answer:
Chandigarh is unlikely to be affected by a cyclone because it is not near the sea or ocean.

Question 8:
Name the ocean which is mainly responsible to bring rain bearing monsoon winds to Kerala coast in June every year.
Answer:
An Indian ocean is mainly responsible to bring rain bearing monsoon winds to Kerala coast in June every year.

Question 9:
Fill in the blanks.
(a) Air around us exerts…………
(b) The moving air is called………….
(c) The main cause of wind movement is uneven………………
(d) High speed wind can cause cyclone in regions of…………
Answer:
(a) Pressure, it is because of this pressure that the leaves of trees or banners flutter when the air moves.
(b) Wind
(c) Heating, wind currents are generated due to the uneven heating on the earth (i.e. between the equator and the poles and of land and water).
(d) Low, a very low-pressure system, with very high speed winds revolving around it, forms a cyclone.

Question 10:
State whether the following statements are True or False.
(a) If wind flows from land to the ocean, then it is day time.
(b) A very high pressure system with very high speed wind surrounding it forms a cyclone.
(c) The coast line of India is not vulnerable to cyclones.
(d) Warm air is lighter than cool air.
Answer:
(a) False, if wind blow from land to the ocean, then it is night time because at night, the water cools down more slowly than the land. So, the cool wind from the land moves towards the ocean.
(b) False, a very low pressure system, with very high speed winds revolving around it, forms a cyclone.
(c) False, the whole coast line of India is vulnerable to cyclones, particularly the east coast.
(d) True, on heating the air expands and occupies more space. When the same thing occupies more space, then it becomes lighter.

Question 11:
To expel hot air out of the kitchen, A has an exhaust fan fitted on the window of her kitchen and B has a similar exhaust fan fitted on the wall near the ceiling of her kitchen. Which of the exhaust fan will expel the hot air more effectively? Explain why.
Answer:
B’s exhaust fan will expel the hot air more effectively because hot air rises up and her fan is at greater height than A’s.

Question 12:
Why is it advisable not to shut all the doors and windows during a storm?
Answer:
During storms, heavy winds passing over the house creates a low pressure. The high pressure inside the house tries to fill the low pressure outside. Since, this pressure is stuck inside the house, therefore, it pushes or lifts the roof off.
So, unless the house is well ventilated, the roof is more likely to blow off in a strong wind.

Question 13:
A flat in Mumbai with a balcony facing the sea has some clothes hung on a clothes line in the balcony. Towards which direction, the clothes will be blown in the afternoon? Explain it.
Answer:
In the afternoon, the land gets heated faster than the water. The air over the land becomes hotter and rises up, creating a drop in pressure. This causes the winds to flow from the sea towards the land.
Thus, the clothes will be blown towards the house because of sea breeze flowing towards the land.

Question 14:
Figure shows a diagrammatic representation of trees in the afternoon along a sea coast. State on which side is the sea, A or fi? Give reasons for your choice.

Answer:
In the afternoon, the air over the land becomes hotter and rises up creating a drop in pressure there. Thus, the wind blows from sea to land, so the sea is on 6 side.

Question 15:
A flag mounted on a flag post near the sea coast flutters in the direction of sea. At what time of the day does this happen — at mid-night or in the afternoon?
Answer:
At night, the water cools down more slowly than the land. So, at mid-night, cool wind from the land moves towards the sea. Therefore, at mid-night the flag mounted on a flag post near the sea’ coast flutters in the direction of sea.

Short Answer Type Questions

Question 16:

Answer:
The correct matching is as given:
(a)-(ii) and (iv), (b)-(i) and (iii).
Air expands on heating and contracts on cooling. Warm air rises up, whereas comparatively cooler air descends (moves down) to that place.

Question 17:
Paheli kept an empty bottle made of plastic inside a refrigerator. After few hours, when she opened the refrigerator, she found the bottle had collapsed. Explain the possible reason.
Answer:
On cooling the air, contraction of air takes place. So, the air inside the bottle contracts due to the low temperature. Hence, the bottle collapses due to the outside pressure.

Question 18:
When strong/high speed wind blows, an umbrella held upright at times gets upturned. Explain the reason.
Answer:
High speed wind passing over the umbrella creates low pressure above the umbrella. Therefore, the pressure below the umbrella upturns it.

Question 19:
Suggest some precautions to be taken to prevent the roof of a tin sheet from flying away during a fierce wind storm.
Answer:
Some precautions are:
(i) Put heavy stones on it.
(ii) Screw it tight.

Long Answer Type Questions

Question 20:
Describe an activity to demonstrate that warm air is lighter than cool air.
Answer:
(i) Take two paper bags of the same size.
(ii) Hang the two bags in the inverted position on the two ends of a wooden stick.
(iii)Tie a piece of thread in the middle of stick and hold the stick by the thread in balance, as shown in the figure (A).}
(iv)Place a burning candle below one of the bags as shown in figure (S).
(v) You will observe that the balance of the bags is disturbed.

This activity indicates that as the warm air rises up it pushes the bag above the candle. This is because on heating, air expands and occupies more space. When same thing occupies more space, it becomes lighter. Thus, we can conclude that warm air is lighter than cool air.

Question 21:
The picture shows tree line along the sea coast on an island near the equator. As shown, the tree tops are permanently bent in one direction. Are the trees bend towards the sea or away from it? Explain.

Answer:
In the given figure, the tree line along the sea coast on an island near the equator shows that tree tops are permanently bent in one direction, i.e. towards the land. The reason behind this movement of trees is that during the day time, the wind blows from sea to land because at this time, land gets warmer more quickly than sea.
This makes the air of land, warm and lighter which is raised up in the sky. Therefore, the top of the bent trees shows the moving direction of wind from sea to land.

Question 22:
Identify the names of six natural phenomena from the following word diagram given as figure.

Answer:

The natural phenomena in the given above crossword are cyclone, thunder, storm and lightning, typhoon and hurricane. A cyclone is called ‘hurricane in the American continent and ‘typhoon’ in Philippines and Japan.