Question 1.
Pressure is defined as:
A. Force × Area
B. Area ÷ Force
C. Force per unit area
D. Mass per unit area
Answer: C. Force per unit area
Question 2.
The SI unit of pressure is:
A. Newton
B. Joule
C. Pascal
D. Watt
Answer: C. Pascal
Question 3.
If the same force acts on a smaller area, the pressure:
A. Decreases
B. Remains the same
C. Becomes zero
D. Increases
Answer: D. Increases
Question 4.
Which part of a dam experiences the greatest water pressure?
A. Top
B. Middle
C. Bottom
D. All parts equally
Answer: C. Bottom
Question 6.
A liquid exerts pressure:
A. Only downward
B. Only upward
C. In all directions
D. Only sideways
Answer: C. In all directions
Question 7.
Atmospheric pressure decreases as we move:
A. Towards sea level
B. Underground
C. Upward to higher altitudes
D. Towards the equator
Answer: C. Upward to higher altitudes
Question 8.
Wind is formed when air moves:
A. From low pressure to high pressure
B. From high pressure to low pressure
C. From hot to cold regions only
D. From mountains to plains only
Answer: B. From high pressure to low pressure
Question 9.
Fast-moving air has:
A. High pressure
B. Low pressure
C. Constant pressure
D. Zero pressure
Answer: B. Low pressure
Question 10.
During a storm, a roof may blow off because:
A. The roof becomes lighter
B. Pressure above the roof is lower than inside the house
C. The roof expands due to heat
D. Rainwater pushes the roof upward
Answer: B. Pressure above the roof is lower than inside the house
Question 11.
Lightning occurs mainly due to:
A. Evaporation of water
B. Separation and discharge of electric charges in clouds
C. Reflection of sunlight
D. Strong winds only
Answer: B. Separation and discharge of electric charges in clouds
Question 12.
The calm central part of a cyclone is called the:
A. Core
B. Centre
C. Eye
D. Ring
Answer: C. Eye
Question 13. A cyclone weakens after moving over land because:
A. Air pressure increases immediately
B. It loses its supply of moisture from the ocean
C. Land is colder than the sea
D. Wind stops blowing
Answer: B. It loses its supply of moisture from the ocean
Question 14.
Which instrument is used to measure air pressure?
A. Thermometer
B. Hygrometer
C. Barometer
D. Anemometer
Answer: C. Barometer
Question 1:
A gardener has two knives to cut thick pumpkin slices. One knife has a very sharp edge, while the other has a blunt edge. He applies the same force with both knives but finds that the sharp knife cuts much more easily.
Answer the following:
a) Which knife produces greater pressure?
b) Explain your answer using the concept of pressure.
c) State the formula for pressure.
Answer:
a) The sharp knife produces greater pressure.
b) Pressure depends on both force and area. Since the sharp knife has a smaller contact area, the same force acts over a smaller area, producing greater pressure. Therefore, it cuts more easily.
c)
$\text{Pressure}=\frac{\text{Force}}{\text{Area}}$
Question 2
An engineer is designing a dam across a river. A trainee suggests making the dam of equal thickness from top to bottom to save construction material.
Do you agree with the trainee? Give reasons based on the behaviour of liquid pressure.
Answer:
No.
Water pressure increases with depth because the weight of the water above becomes greater. The bottom of the dam experiences the maximum pressure. Therefore, the base must be wider and stronger to withstand this greater pressure and ensure the dam remains stable.
Question 3
During a severe storm, the roof of a small house is blown away even though the walls remain undamaged.
Using the concept of air pressure, explain why this happens.
Answer:
During a storm, air moves rapidly over the roof, creating a region of low pressure above it. The air inside the house remains at relatively higher pressure. This pressure difference exerts an upward force on the roof, which may lift and blow it away.
Question 4:
Four friends are caught outside during a thunderstorm.
Rahul stands under a tall tree.
Meera enters a nearby building.
Arjun stands in an open field.
Neha shelters under a metal shed.
Who has chosen the safest option? Justify your answer.
Answer:
Meera has chosen the safest option.
A properly constructed building provides protection during a thunderstorm. Tall trees are more likely to be struck by lightning, while open fields expose people to lightning. Therefore, taking shelter inside a building is the safest choice.
Question 5:
Meteorologists observe a large low-pressure region forming over the sea. The surrounding winds are moving rapidly towards this region.
Based on these observations, answer the following:
a) What weather system is likely to develop?
b) Why are the surrounding winds moving towards the centre?
c) Why is early weather forecasting important in this situation?
Answer:
a) A cyclone is likely to develop.
b) Air always moves from regions of higher pressure to regions of lower pressure. Therefore, winds move towards the low-pressure centre.
c) Early forecasting allows authorities to issue warnings, evacuate vulnerable areas, and help people take safety measures before the cyclone arrives.
Question 6
How does the study of air pressure and wind help in weather forecasting?
Answer:
Meteorologists study patterns of air pressure and wind movement to identify developing storms and cyclones. This information helps them predict weather conditions and issue early warnings so that people can take safety measures in advance.
Question 7
State the important safety measures to be followed before, during and after a cyclone.
Answer:
Before a cyclone
Follow weather forecasts and warnings.
Secure loose objects.
Store drinking water and essential food supplies.
During a cyclone
Stay indoors.
Keep away from windows.
Switch off electricity if necessary.
After a cyclone
Avoid damaged areas.
Drink only clean and safe water.
Help affected people while following safety precautions.
Question 8:
How does air pressure change with altitude? Why do mountaineers carry oxygen cylinders?
Answer:
Atmospheric pressure decreases with increasing altitude. As the pressure decreases, the amount of available oxygen also becomes lower. Therefore, mountaineers carry oxygen cylinders to help them breathe at high altitudes.
Question 9
How does a lightning conductor protect a building?
Answer:
A lightning conductor provides a safe path for electric charge to travel from the building to the ground. This prevents the lightning from damaging the building.
Question 10
Why does a balloon expand when air is blown into it?
Answer:
The air blown into the balloon exerts pressure equally in all directions on the inner walls of the balloon. This pressure stretches the rubber, causing the balloon to inflate.