Key Concept: Applications of Pressure

d) The smaller area of a sharp edge increases pressure
[Solution Description]
A sharp knife has a smaller contact area, which increases the pressure for the same force applied, making cutting easier:
$Pressure = \frac{Force}{Area}$
Lower area leads to higher pressure.

Key Concept: Pressure, Force and Area

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
The Assertion states that the pressure exerted by a liquid depends only on the height of the liquid column and not on the shape or cross-sectional area of the container. This is true because pressure at any point in a liquid is given by $P = \rho g h$, where $\rho$ is the density of the liquid, $g$ is the acceleration due to gravity, and $h$ is the height of the liquid column. The Reason states that pressure in liquids is transmitted equally in all directions due to Pascal's principle, which is also true. However, Pascal's principle explains how pressure is distributed, not why it depends only on the height. Therefore, the Reason does not correctly explain the Assertion.

Key Concept: Practical Application

b) Sharp knife reduces area, increasing pressure
[Solution Description]
A sharp knife has a smaller edge area compared to a blunt knife. Since $P = \frac{F}{A}$, for the same applied force, the pressure is higher when the area is smaller. Thus, the sharp knife cuts more easily due to higher pressure.

Key Concept: Definition of Pressure

d) Assertion is false, but Reason is true.
[Solution Description]
The assertion (A) claims that a sharp knife exerts less pressure on vegetables compared to a blunt knife, making cutting easier. However, this is incorrect because according to the formula $Pressure = \frac{Force}{Area}$, reducing the area (as with a sharp knife) increases pressure, not decreases it. Therefore, the assertion is false.
The reason (R) states correctly that the area of contact is smaller for a sharp knife, leading to higher pressure. This explanation aligns with the definition of pressure but contradicts the assertion. Hence, the reason is true.
Combining these observations:
1. Assertion (A) is false.
2. Reason (R) is true.

Key Concept: Practical Unit of Air Pressure

b) Millibar (mb)
[Solution Description]
While the SI unit of pressure is pascal (Pa), the practical unit of air pressure is millibar (mb), where 1 mb = 100 Pa.

Key Concept: Pressure Calculation

c) 40 Pa
[Solution Description]
Pressure is calculated using the formula $P = \frac{F}{A}$. Here, $F = 200\,N$ and $A = 5\,m^2$. Substituting the values, we get:
$P = \frac{200\,N}{5\,m^2} = 40\,N/m^2 = 40\,Pa$
Thus, the pressure is 40 Pa.

Key Concept: Pressure, Force Distribution, Applications

c) It increases the pressure due to smaller contact area
[Solution Description]
A sharp knife has a smaller edge area, so the same force is applied over a smaller area, resulting in higher pressure, which makes cutting easier.

Key Concept: Pressure and Area Relationship

c) Assertion is true, but Reason is false.
[Solution Description]
The assertion is correct because a sharp knife has a smaller area of contact compared to a blunt one for the same force, which leads to higher pressure according to $P = \frac{F}{A}$. However, the reason is incorrect because pressure is inversely proportional to the area of contact for a given force, not directly proportional. Therefore, the assertion is true, but the reason is false.

Key Concept: Pressure: Practical Examples

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that a blunt knife requires more effort to cut an apple compared to a sharp knife. This is true because a blunt knife has a larger surface area in contact with the object being cut, which spreads the force over a greater area, resulting in lower pressure ($P = \frac{F}{A}$).
The reason explains that the force is spread over a larger area, reducing pressure, which directly supports why the assertion is true. Hence, both the Assertion and Reason are true, and the Reason correctly explains the Assertion.

Key Concept: Pressure, Load Distribution

b) 6366 Pa
[Solution Description]
First, calculate the area of the cloth: $A = \pi r^2 = \pi (0.1\,m)^2 = 0.0314\,m^2$. Then, pressure $P = \frac{F}{A} = \frac{200\,N}{0.0314\,m^2} \approx 6366\,Pa$.

Key Concept: Pressure Exerted by Air

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that a rubber sucker sticks to a smooth surface when pressed because the air pressure inside becomes lower than the atmospheric pressure outside. This is correct because pressing the sucker removes most of the air inside, creating a lower pressure zone compared to the higher external atmospheric pressure. The reason given is also correct: atmospheric pressure acts in all directions and exerts a force on the sucker, making it hard to pull off. Furthermore, the reason correctly explains the assertion, as the external atmospheric pressure's force is what keeps the sucker stuck due to the pressure difference. Therefore, both the assertion and reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Pressure Exerted by Air

d) The atmospheric pressure exerts a greater force due to the larger area of the unfolded sheet.
[Solution Description]
The unfolded chart paper has a larger surface area exposed to atmospheric pressure than the folded one. The air exerts force on the sheet, and because pressure is force per unit area ($P = F/A$), a larger area means greater total force acting downward. Thus, more effort is required to overcome this increased force when lifting the plate.

Key Concept: Atmospheric Pressure

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The Assertion states that atmospheric pressure is the force exerted by air on all objects, which is correct as discussed in the syllabus. The Reason explains that air exerts pressure because it has mass and occupies space, which is also true and correctly explains the Assertion since the weight of air molecules creates pressure.

Key Concept: Activity-Based Question

d) Air exerts greater pressure on the larger area of the unfolded sheet
[Solution Description]
Air exerts force on the surface area in contact. Since the unfolded sheet has a larger area than the folded one, the total force (and thus pressure) acting on it increases, requiring more effort to lift.

Key Concept: Atmospheric pressure, force calculation

d) 2,250 N
[Solution Description]
First, convert the area from \(\mathrm{cm}^2 \rightarrow \mathrm{m}^2\) : $15 \text{ cm} \times 15 \text{ cm} = 225 \text{ cm}^2 = 0.0225 \text{ m}^2$.
Atmospheric pressure is given as $100 \text{ kPa} = 100,000 \text{ Pa} = 100,000 \text{ N/m}^2$.
Force required to overcome atmospheric pressure is calculated using $F = P \times A$:
$F = 100,000 \text{ N/m}^2 \times 0.0225 \text{ m}^2 = 2,250 \text{ N}$.

Key Concept: Magnitude of Atmospheric Pressure

c) The pressure inside our body balances the atmospheric pressure
[Solution Description]
Atmospheric pressure exerts a large force, but our body’s internal pressure balances it, preventing us from being crushed. This equilibrium ensures no net force acts on our bodies.

Key Concept: Force calculation, Pressure-area relationship

c) 6 N
[Solution Description]
1) Given: Force $F_1 = 12$ N for area $A_1 = 0.392$ m$^2$.
2) New area $A_2 = A_1/2 = 0.196$ m$^2$.
3) Since pressure $P = F/A$ is constant (atmospheric pressure), $P = \frac{F_1}{A_1} = \frac{F_2}{A_2}$.
4) Thus, $F_2 = \frac{F_1 × A_2}{A_1} = \frac{12 × 0.196}{0.392} = 6$ N.

Key Concept: SI Unit of Pressure

c) Pascal (Pa)
[Solution Description]
The SI unit of pressure is newton per square meter ($N/m^2$), also called pascal (Pa). Other units like millibar (mb) or hectopascal (hPa) are derived from it, where 1 mb = 100 Pa and 1 hPa = 100 Pa. The question tests recall of the fundamental unit.

Key Concept: Pressure Exerted by Air, Surface Area Effect

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
In the given experiment, the assertion states that more effort is needed to lift the paper plate when covered with an unfolded sheet than a folded one, which is true as observed in Activity 6.3. The reason claims this is due to higher atmospheric pressure on the unfolded sheet because of its larger surface area, which is also true. Moreover, the reason correctly explains the assertion since atmospheric pressure acts on all surfaces, and its effect increases with the surface area exposed to air. Hence, both the assertion and reason are true, and the reason is the correct explanation for the assertion.

Key Concept: Air Pressure Experiment

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that more effort is needed to lift the paper plate with an unfolded chart paper than a folded one, which matches observations from Activity 6.3. The reason explains this phenomenon by stating that air exerts pressure on the sheet's surface area, and since $\text{Pressure} = \frac{\text{Force}}{\text{Area}}$, a larger area increases the force exerted by air pressure. Therefore, both statements are true, and the reason correctly explains the assertion.

Key Concept: Pressure equilibrium

d) The air pressure in both balloons becomes equal.
[Solution Description]
The air flow stops when the pressure inside both balloons becomes equal. Initially, air flows from the inflated (high-pressure) balloon to the uninflated (low-pressure) balloon. Once the pressures balance, there is no further net movement of air, and both balloons reach nearly the same size.

Key Concept: Pressure gradient application

d) Air would flow until pressures equalize, with the balloon shrinking noticeably.
[Solution Description]
The inflated balloon's high-pressure air would flow into the rigid container (which initially has lower pressure) until pressures equalize. Since the container cannot expand, the balloon would shrink significantly while the container's pressure increases minimally due to its large volume. The final sizes wouldn't equalize unlike with two balloons.

Key Concept: Effect of air pressure, Pressure equilibrium

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
In the given scenario, the inflated balloon has higher internal pressure compared to the uninflated one. According to the concept of pressure equilibrium, air will flow from the high-pressure region (inflated balloon) to the low-pressure region (uninflated balloon) through the straw. The flow continues until the pressures in both balloons become equal, resulting in both balloons attaining similar sizes. The reason correctly explains why the air moves, as it aligns with the principle that air moves from high to low pressure regions. Therefore, both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Key Concept: Air Pressure

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description] When air is blown into a balloon, it fills the space inside and exerts pressure on the inner walls of the balloon. This pressure acts equally in all directions, causing the balloon to expand uniformly. The reason correctly explains why the balloon expands in all directions because air indeed exerts pressure uniformly in all directions.

Key Concept: Units of pressure, Real-world application

d) 100,000 Pa
[Solution Description]
First, convert mass to force: $F = mg = 225 \, \text{kg} \times 10 \, \text{m/s}^2 = 2250 \, \text{N}$. Then, convert area to square meters: $225 \, \text{cm}^2 = 0.0225 \, \text{m}^2$. Pressure $P = F/A = 2250 / 0.0225 = 100,\!000 \, \text{Pa}$ (or $1000 \, \text{hPa}$).

Key Concept: Pressure and Area

b) 10 $N/m^2$
[Solution Description]
The pressure exerted can be calculated using the formula: $P = \frac{F}{A}$. Here, $F = 50\;N$ and $A = 5\;m^2$. Substituting these values into the formula gives:
$P = \frac{50}{5} = 10\;N/m^2$
Therefore, the pressure exerted is 10 $N/m^2$.

Key Concept: Pressure-area relationship, Atmospheric force

d) Pressure exerts more force over larger areas.
[Solution Description]
When unfolded, the chart paper has a larger surface area exposed to atmospheric pressure. Since pressure is force per unit area ($P = F/A$), a larger area means greater total force exerted by atmospheric pressure downward, requiring more effort to lift the plate. This demonstrates that atmospheric pressure acts over surfaces, and its effect scales with area.

Key Concept: Air Pressure's Role in Daily Life

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that a rubber sucker sticks to a smooth surface because of the difference in air pressure, which is correct. When the sucker is pressed against a smooth surface, most of the air inside is pushed out, reducing the internal pressure. The external atmospheric pressure, being higher, exerts a force that keeps the sucker firmly attached to the surface. The reason correctly explains why this happens: it describes the process of expelling air from inside the sucker, creating a low-pressure region, and how the higher external pressure maintains the attachment. Therefore, both the assertion and reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Effect of high-speed winds on pressure

d) A low-pressure area forms above the roof
[Solution Description]
High-speed winds create a low-pressure area above the roof. The higher air pressure inside the house pushes the roof upwards due to the pressure difference, which can cause the roof to be blown off if it's weak.

Key Concept: Pressure difference and wind direction

c) Difference in air pressure between regions
[Solution Description]
Air moves from a region of high pressure to a region of low pressure due to the pressure difference between the two regions. This movement of air is what we perceive as wind.

Key Concept: Formation of Wind

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The Assertion states that during the day, wind blows from the sea to the land because of the formation of a low-pressure region over the land. This is true as the land heats up faster than water, causing the air above it to warm up, rise, and create a low-pressure area. The Reason explains the cause of this phenomenon by stating that land gets heated faster, leading to the rising of air and creation of a low-pressure area. Since the Reason correctly explains the Assertion, both are true and logically connected.

Key Concept: Pressure difference, Wind formation

a) Wind is formed with speed proportional to the pressure difference.
[Solution Description]
When air moves from a high-pressure region to a low-pressure region, it results in the formation of wind. The greater the pressure difference, the faster the wind speed. This is because nature tends to balance pressure differences by moving air from areas of higher pressure to areas of lower pressure.

Key Concept: Pressure difference, Wind speed

b) 0.5 N
[Solution Description]
The force exerted by the air can be calculated using the pressure difference and the area of the straw. First, convert the pressures to pascals: $P_1 = 1100 \text{ mb} = 1100 \times 100 \text{ Pa} = 110000 \text{ Pa}$, $P_2 = 1050 \text{ mb} = 105000 \text{ Pa}$. The pressure difference is $\Delta P = P_1 - P_2 = 5000 \text{ Pa}$. Using the formula for pressure, $Force = \Delta P \times Area = 5000 \times 10^{-4} = 0.5 \text{ N}$.

Key Concept: Land and Sea Breeze

d) Low pressure develops over the land
[Solution Description]
During the day, land heats up faster than water, creating a low pressure area over the land. The cooler air from the high pressure region over the sea moves towards the land, resulting in a sea breeze.

Key Concept: Sea breeze, Pressure gradient

b) 0.083 m/s$^2$
[Solution Description]
The pressure gradient force per unit mass is calculated as $\frac{1}{\rho} \frac{\Delta P}{\Delta x}$. First, convert the pressure difference to pascals: $\Delta P = 1010 \text{ mb} - 990 \text{ mb} = 20 \text{ mb} = 2000 \text{ Pa}$. The distance $\Delta x = 20 \text{ km} = 20000 \text{ m}$. The force per unit mass is $\frac{1}{1.2} \times \frac{2000}{20000} = \frac{1}{12} \approx 0.0833 \text{ m/s}^2$.

Key Concept: Unit of Pressure

b) Pascal ($Pa$)
[Solution Description]
The SI unit of pressure is $N/m^2$, also known as pascal ($Pa$). Other units like millibar ($mb$) and hectopascal ($hPa$) are derived from it but are not the standard SI unit.

Key Concept: Formation of Wind, Pressure Differences

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that during the day, sea breeze occurs due to warm air rising over the land, creating a low-pressure area, which causes cooler air from the sea (high-pressure area) to move toward the land. This is correct as per the concept of pressure differences in wind formation. The reason explains the general principle that air moves from high-pressure regions to low-pressure regions until equilibrium is reached, which directly explains why the sea breeze occurs. Both are true, and the reason correctly explains the assertion.

Key Concept: Thunderstorms, Pressure difference

d) The pressure difference between outside and inside the house lifts the roof.
[Solution Description]
High-speed winds create a low-pressure area above the roof. The pressure inside the house remains higher, creating a pressure difference. If this difference is large enough and the roof is weak, it can be blown away. Keeping windows open equalizes the pressure.

Key Concept: Formation of Wind

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
During the day, the land heats up faster than the sea due to differences in specific heat capacity. This causes the air above the land to warm up and rise, creating a low-pressure region. Cooler air from the higher-pressure region over the sea moves toward the low-pressure region over the land, resulting in a sea breeze. Thus, both Assertion (A) and Reason (R) are true, and Reason (R) correctly explains Assertion (A).

Key Concept: Warm air rising and cool air sinking

d) Warm air rises over the land, creating a low-pressure zone that draws in cooler air from the sea.
[Solution Description]
On a typical sunny day, the land heats up faster than the sea. This causes the air above the land to become warmer and rise, creating a low-pressure area. To balance this, cooler air from the higher pressure region over the sea moves towards the land, forming what is known as a sea breeze.

Key Concept: Sea Breeze and Pressure Differences

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that during the day, the wind blows from the sea to the land because the land is warmer than the sea. This is true as per the syllabus, which explains that during the day, the land becomes warmer and lighter, creating a low-pressure area. The reason given is that the land heats up faster than the sea during the day, creating a low-pressure region over the land. This is also true and correctly explains why the wind blows from the high-pressure sea to the low-pressure land, resulting in a sea breeze. Therefore, both the assertion and the reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Sea and Land Breezes

b) The land heats up faster than the sea, causing air to move from the sea to the land.
[Solution Description]
The land heats up faster than the sea during the day, causing the air above it to warm and rise, creating a low-pressure area. The cooler, high-pressure air over the sea moves towards the land, resulting in a sea breeze.

Key Concept: Pressure Differences, Sea Breeze

b) 1007 hPa
[Solution Description]
During the day, land heats up faster than the sea, creating a low-pressure area over the land. The cooler air over the sea has higher pressure, causing a sea breeze. Since the land pressure is given as 1005 hPa (low pressure), the sea pressure must be higher. Typically, pressure differences for sea breezes range between 2-4 hPa. Thus, the sea pressure is approximately 1007 hPa to 1009 hPa.

Key Concept: Land Breeze, Pressure Differences

c) Low pressure over sea, high pressure over land
[Solution Description]
At night, land cools faster than the sea, creating high pressure over the land and low pressure over the sea. The pressure difference drives the land breeze. Since wind speed $\propto$ pressure difference, the larger the temperature difference, the greater the pressure gradient. Given the land is colder ($15^\circ C$) and the sea is warmer ($20^\circ C$), the pressure gradient will cause air to flow from land (high pressure) to sea (low pressure).

Key Concept: High-speed winds and air pressure

c) The balloons move towards each other due to reduced pressure between them.
[Solution Description]
When high-speed wind is blown between the two balloons, it creates a low-pressure region between them. The higher air pressure on the outer sides of the balloons pushes them towards each other. This demonstrates that high-speed winds lower air pressure.

Key Concept: Bernoulli's principle, Airflow dynamics

c) Low pressure forms between them due to fast airflow
[Solution Description]
When air is blown between the balloons, the speed of airflow increases, creating a low-pressure region between the balloons (as per Bernoulli's principle). The surrounding higher-pressure air exerts a force on the outer surfaces of the balloons, pushing them towards each other. Hence, the movement occurs due to the pressure difference caused by high-speed airflow.

Key Concept: High-Speed Winds Result in Lowering of Air Pressure

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
According to the syllabus, high-speed winds blowing over a surface create a low-pressure area because the fast-moving air reduces the number of air molecules applying force per unit area. This explains why roofs may be blown off during storms when high-speed winds lower the pressure outside while higher pressure inside pushes upward. Therefore, the Assertion is true because high-speed winds indeed reduce air pressure, and the Reason correctly explains this phenomenon by describing how fast-moving air leads to fewer air molecules exerting pressure.

Key Concept: High-Speed Winds Result in Lowering of Air Pressure, Bernoulli's Principle

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that keeping doors and windows closed during a storm increases the likelihood of roofs blowing off. This is true because when high-speed winds pass over the roof, they create a low-pressure area above it (Bernoulli's principle). If the house remains airtight (doors/windows closed), the higher air pressure inside the house exerts an upward force on the roof, potentially causing it to blow off. The reason correctly explains this phenomenon using Bernoulli's principle, which relates high-speed winds ($v$) and reduced pressure ($P$): $P + \frac{1}{2} \rho v^2 = \text{constant}$. Thus, both assertion and reason are true, and the reason is the correct explanation for the assertion.

Key Concept: Practical Example of Low Pressure

c) The balloons move towards each other.
[Solution Description]
Blowing air between two balloons increases the wind speed in that region, creating a low-pressure area between them. The surrounding higher-pressure air pushes the balloons inward, causing them to come closer together. This illustrates how high-speed winds reduce pressure.

Key Concept: Pressure Difference Due to High-Speed Winds

b) The high pressure inside the house pushes the roof up as low pressure forms outside.
[Solution Description]
During storms, high-speed winds pass over the roof, reducing the air pressure above it. The higher air pressure inside the house pushes upwards on the roof due to this pressure difference. If the pressure difference is large enough, it can lift and blow the roof off. This demonstrates how high-speed winds create low-pressure areas.

Key Concept: High-speed winds and air pressure

b) Air pressure decreases
[Solution Description]
When high-speed winds blow over a surface, they create a region of lower air pressure because the fast-moving air reduces the pressure in that area. This is due to Bernoulli's principle, which states that increasing the speed of a fluid decreases its pressure.

Key Concept: Wind Speed and Pressure Relationship

b) Air pressure decreases due to fewer molecular collisions.
[Solution Description]
According to Bernoulli's principle, an increase in wind speed leads to a decrease in air pressure. When wind blows faster over a surface, the kinetic energy of the air molecules increases, causing fewer collisions per unit area, resulting in lower pressure in that region.

Key Concept: Air Pressure, Speed-Pressure Relationship

c) The distance will decrease less in the second case.
[Solution Description]
According to Bernoulli's principle, lower airspeed results in higher pressure between the balloons. Reduced blowing speed means less pressure difference is created, so the balloons will move towards each other slower.
For 20 m/s: Distance decreases significantly as balloons accelerate faster due to high pressure difference.
For 10 m/s: Distance decreases at half the rate since pressure difference is smaller.
After 2 seconds, the distance covered in the second case will be less than in the first case, meaning the balloons will be farther apart compared to the first scenario.

Key Concept: Effect of Blowing Harder on Balloons

c) They move towards each other faster.
[Solution Description]
Blowing harder increases the speed of the air between the balloons, further reducing the air pressure in that region. The greater difference in pressure compared to the surrounding air causes the balloons to move towards each other at a faster rate.

Key Concept: High-Speed Winds and Air Pressure

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that when air is blown between two inflated balloons, they move towards each other, which is observed in Activity 6.6. This happens because blowing air between the balloons increases wind speed in the gap, reducing air pressure (Bernoulli’s principle). The higher pressure outside then pushes the balloons together. The reason correctly explains why this occurs by linking high-speed wind to low pressure and the resulting pressure difference.

Key Concept: Pressure Gradient, Force Calculation

c) 0.4 N
[Solution Description]
The pressure difference ($\Delta P$) is proportional to the square of the airspeed ($v^2$). If $v$ doubles from 30 m/s to 60 m/s, $\Delta P$ becomes $(60/30)^2 = 4$ times larger.
Since force ($F$) is directly proportional to $\Delta P$, the new force will also be 4 times the original:
$F_{\text{new}} = 4 \times 0.1\,\text{N} = 0.4\,\text{N}$.

Key Concept: Pressure reduction, Wind speed

b) 98,900 Pa
[Solution Description]
Given:
- Initial pressure ($P_{\text{initial}}$) = $1.02 \times 10^5$ Pa
- Pressure reduction = 3% of initial pressure
Step 1: Calculate pressure reduction amount
$0.03 \times 1.02 \times 10^5 = 3060$ Pa
Step 2: Calculate new pressure
$1.02 \times 10^5 - 3060 = 0.9894 \times 10^5$ Pa = $98,940$ Pa
Therefore, the new pressure is approximately 98,900 Pa

Key Concept: High-speed winds, pressure difference, structural impact

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
High-speed winds create low pressure over the roof while the air pressure inside the house remains higher if the roof is sealed. This pressure difference can cause the roof to lift or blow off. When doors and windows are open, air flows through the house, reducing the pressure difference between the inside and outside. Thus, both Assertion and Reason are true, and the Reason correctly explains why open doors and windows prevent roofs from being blown off.

Key Concept: Unit of Pressure

b) Pascal ($Pa$)
[Solution Description]
The SI unit of pressure is $N/m^2$, also known as pascal ($Pa$). Other units like millibar ($mb$) and hectopascal ($hPa$) are also used, but $Pa$ is the standard SI unit.

Key Concept: Bernoulli's Principle Application

c) The balloons move closer together due to reduced pressure between them
[Solution Description]
Blowing air between the balloons creates a low-pressure region in between. The higher pressure on the outer sides of the balloons pushes them toward each other. This demonstrates Bernoulli's principle, where increased air speed results in decreased pressure.

Key Concept: Lightning formation, Charge separation

d) Strong winds rubbing against each other
[Solution Description]
The charge separation in thunderclouds is caused by strong winds rubbing against each other, creating static electric charges. Positively charged ice particles move upwards while negatively charged water droplets remain in the lower part of the cloud. This separation builds up until a discharge (lightning) occurs.

Key Concept: Formation of thunderstorms and lightning

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
The assertion states that lightning occurs due to the sudden flow of charges when the insulating property of air breaks down, which is correct as per the syllabus. The reason mentions that rapid heating of air around lightning causes expansion, resulting in thunder, which is also true as per the syllabus. However, the reason does not explain why lightning occurs but instead explains the phenomenon of thunder, which is a consequence of lightning. Therefore, both are true, but the reason is not the correct explanation of the assertion.

Key Concept: Charge Separation in Clouds

b) Positive and negative charges separate within the cloud
[Solution Description]
Strong winds blowing upwards and downwards cause rubbing between water droplets and ice particles, leading to the development of static electric charges. The positively charged lighter ice particles move to the upper part of the cloud, while the negatively charged heavier water droplets occupy the lower part, creating charge separation.

Key Concept: Local thunderstorms, Climate phenomena

c) Bordoisila
[Solution Description]
Bordoisila is a local thunderstorm specific to Assam, characterized by strong winds and heavy rainfall. It occurs during pre-monsoon months.

Key Concept: Safety Measures During Cyclones

d) To equalize air pressure inside and outside the house
[Solution Description]
Keeping doors and windows open allows wind to flow through the house, reducing the pressure difference between the inside and outside. This minimizes the risk of the roof being blown away due to high pressure inside.

Key Concept: Pressure difference, Wind speed, Roof stability

b) It reduces the pressure difference between the inside and outside of the house.
[Solution Description]
High-speed winds create a low-pressure area above the roof, while the air pressure below remains higher. This difference can cause roofs to blow off. Keeping doors and windows open allows wind to flow through the house, balancing the pressure inside and outside, thus reducing the net force on the roof.

Key Concept: Cyclone formation, Pressure systems, Eye wall dynamics

c) Descending air in the eye inhibits cloud formation and wind activity.
[Solution Description]
The eye forms due to descending air, which suppresses cloud formation and reduces wind speed, creating a low-pressure center. Surrounding the eye is the eyewall, where rising warm moist air leads to intense thunderstorms and high-speed winds.

Key Concept: Formation of Storms

d) Low pressure above the roof and high pressure below it
[Solution Description]
High-speed winds create a low-pressure area above the roof, while the air pressure inside the house remains higher. The large pressure difference can cause weak roofs to be blown away.

Key Concept: Role of Warm Air in Thunderstorms

c) It leads to condensation and cloud formation
[Solution Description]
Warm and moist air rises because it is lighter, creating a low-pressure area. Cooler air from surrounding high-pressure areas moves in to replace it, forming wind circulation. As the rising air expands and cools, moisture condenses into water droplets, leading to cloud formation. Eventually, these droplets merge and fall as rain, hail, or snow.

Key Concept: Thunderstorm formation, Charge separation in clouds

d) Assertion is false, but Reason is true.
[Solution Description]
The Assertion claims that lightning occurs exclusively between a cloud and the ground due to maximum charge separation there, which is false. Lightning can occur within a cloud, between clouds, or between a cloud and the ground. The Reason correctly describes the charge distribution in a thundercloud but does not justify the Assertion, as it explains general charge separation, not ground-specific phenomena.

Key Concept: Charge Separation in Clouds

c) Friction between water droplets and ice particles creates opposite charges
[Solution Description]
Strong upward and downward winds cause friction between water droplets and ice particles, leading to static electric charges. Positively charged lighter ice particles move to the upper part of the cloud, while negatively charged heavier water droplets occupy the lower part. This results in charge separation.

Key Concept: Thunderstorms and Lightning, Regional Variations

c) Assam; helps kharif crops and mango ripening
[Solution Description]
Bordoisila is a local name for thunderstorms in Assam. These thunderstorms occur before the monsoon and are crucial for agriculture. They provide necessary rainfall for kharif crops and aid in ripening mangoes, supporting regional farming activities.

Key Concept: Static charge development within clouds leading to lightning

d) Assertion is false, but Reason is true.
[Solution Description]
The Assertion states that lightning occurs only when a cloud is negatively charged at the bottom and the ground is positively charged. This is false because lightning can also occur within a single cloud (intra-cloud lightning) or between two different clouds (inter-cloud lightning). The Reason, however, is true as it correctly describes the process of charge separation in clouds due to the rubbing of water droplets and ice particles from strong winds.

Key Concept: Safety during thunderstorms

c) Staying inside a car with windows closed
[Solution Description]
During a thunderstorm, staying inside a car or bus is safer because their metal bodies act as a shield against lightning, provided you do not touch any metallic parts.

Key Concept: Static charge separation, Lightning mechanism

c) 10$^5$ V/m
[Solution Description]
The electric field strength ($E$) is calculated using the formula $E = \frac{V}{d}$, where $V$ is the potential difference and $d$ is the distance. Given $V = 10^8$ V and $d = 1$ km = $1000$ m, substitute the values:
$E = \frac{10^8}{1000} = 10^5 \text{ V/m}$

Key Concept: Lightning formation

b) When static charges accumulate sufficiently to break down the insulating property of air
[Solution Description]
Lightning occurs when the build-up of opposite charges becomes large enough to overcome the insulating property of air, causing a sudden discharge of electricity.

Key Concept: Charge Separation in Clouds

c) Rubbing between water droplets and ice particles due to wind movement
[Solution Description]
The charge separation in a thundercloud occurs due to the upward and downward movement of strong winds, which cause rubbing between water droplets and ice particles. This friction results in static electric charges. Positively charged lighter ice particles move upwards, while negatively charged heavier water droplets settle at the lower part of the cloud.

Key Concept: Formation of Thunder

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that thunder is produced due to rapid expansion of air caused by the intense heat from lightning. According to the syllabus, thunder indeed results from the explosive expansion of air heated by lightning. The reason explains that lightning involves a sudden flow of electric charges, which heats the air. This directly supports the assertion because the mechanism described in the reason leads to the effect mentioned in the assertion. Thus, both statements are true, and the reason correctly explains the assertion.

Key Concept: Precautions During Thunderstorms

c) Using an umbrella with a metallic rod
[Solution Description]
The syllabus advises avoiding tall objects, staying away from open water, and not lying flat on the ground. Using an umbrella with a metallic rod is unsafe because metal conducts electricity, increasing the risk of being struck by lightning. Seeking shelter inside a car or low-lying area is safer.

Key Concept: Charge Separation in Clouds

b) Friction between rising and falling ice and water particles
[Solution Description]
According to the syllabus, strong winds blowing upwards and downwards facilitate rubbing between water droplets and ice particles. This friction causes static electric charges to develop, with positively charged lighter ice particles moving to the upper part of the cloud and negatively charged heavier water droplets occupying the lower part. Thus, charge separation occurs due to the movement and collision of these particles.

Key Concept: Cyclone Formation and Characteristics

c) Assertion is true, but Reason is false.
[Solution Description]
The assertion states that the eye of a cyclone has calm winds and clear skies, which is true because it is a region of descending air that suppresses cloud formation. However, the reason claims that the eye forms due to subsidence of warm air, which is incorrect. The eye forms due to the centrifugal force balancing the pressure gradient force, resulting in minimal wind movement. Thus, the Assertion is true, but the Reason is false.

Key Concept: Cyclone Formation

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
According to the syllabus, cyclones indeed form over warm ocean waters where warm, moist air rises, creating a low-pressure area. This is correctly explained by the fact that Earth's rotation (Coriolis effect) causes the moving air to spin, forming a cyclone. Both statements are true, and the reason accurately explains the assertion.

Key Concept: Cyclone formation, Pressure difference

b) $0.167 \, \text{hPa/km}$
[Solution Description]
The pressure gradient is calculated as the change in pressure divided by the distance over which this change occurs. Here, the pressure difference is $1000 \, \text{hPa} - 950 \, \text{hPa} = 50 \, \text{hPa}$. The distance is 300 km.
Therefore, the pressure gradient is:
$\frac{50 \, \text{hPa}}{300 \, \text{km}} = \frac{1}{6} \, \text{hPa/km} \approx 0.167 \, \text{hPa/km}$

Key Concept: Cyclone Impact

c) Earthquakes due to wind pressure
[Solution Description]
Cyclones cause destruction through strong winds, storm surges, and heavy rains, but they do not typically trigger earthquakes.

Key Concept: Impact

c) Strong winds, heavy rain, and storm surges
[Solution Description]
When a cyclone reaches land, it loses its source of moist air and weakens, but before that, it causes destruction through strong winds, heavy rainfall, storm surges, and flooding. The text explains: "Once the cyclone reaches land, the source of moist air is cut off and it gradually loses its strength... Cyclones can be extremely destructive..."

Key Concept: Formation Process

c) Over warm ocean waters
[Solution Description]
Cyclones form over warm ocean waters due to differences in temperature and pressure. The text states: "Cyclones are large storms that form over warm ocean waters."

Key Concept: Energy release, Cyclone formation

c) It provides energy to sustain and intensify the cyclone.
[Solution Description]
When water vapor condenses into raindrops, latent heat is released into the atmosphere. This additional heat warms the surrounding air, causing it to rise further, reducing surface pressure, and intensifying the cyclone by drawing more air inward, thus sustaining the storm's energy.

Key Concept: Storm surge, Cyclone impact

c) Widespread flooding and saltwater intrusion.
[Solution Description]
A storm surge is a rapid rise in sea level caused by a cyclone's strong winds pushing water toward the shore. A 10-meter surge can flood coastal regions extensively, damaging infrastructure, contaminating freshwater sources, and causing loss of life due to drowning or structural collapse.

Key Concept: Safety Measures, High-speed winds

b) Constructing cyclone-resistant buildings
[Solution Description]
For cyclones with high wind speeds like 250 km/h, the most effective safety measures include early warning systems for evacuation and sturdy shelters to withstand the winds. Public awareness campaigns and timely IMD alerts are also crucial. Among the options, constructing cyclone-resistant buildings provides long-term protection against such high-speed winds.

Key Concept: Structure of a cyclone: Eye of the cyclone

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that the eye of a cyclone is a region of low atmospheric pressure, which is true as per the syllabus. The reason explains that the calm wind in the eye is due to descending air that warms up and suppresses cloud formation, which is also correct and provides the explanation for why the eye has calm winds. Therefore, both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Key Concept: Eye of the Cyclone

c) The area of low pressure at the center with calm winds
[Solution Description]
The eye of a cyclone is the central region where the atmospheric pressure is the lowest. It is characterized by calm winds and clear skies, while the surrounding areas experience high-speed winds and heavy rain.

Key Concept: Structure of a cyclone: Eye of the cyclone

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that the eye of a cyclone has calm weather conditions, which is true as the eye is known for its calm and clear skies. The reason explains that the eye has the lowest pressure, causing air to descend and suppress wind formation, which is also true. Furthermore, the reason correctly explains why the eye has calm weather conditions. Therefore, both the assertion and reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Impact of Cyclones on Agriculture

c) Salt from seawater makes the soil less fertile, reducing crop yields.
[Solution Description]
When seawater floods agricultural land due to a cyclone, the high salt content in the water can make the soil less fertile. This reduces crop productivity for months or even years until the salt is washed away naturally or through human intervention such as soil treatment.

Key Concept: Impact of Cyclones on Land, Flooding

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that storm surges from cyclones can flood coastal and inland areas due to high water walls. This is true because cyclones generate powerful winds that push seawater, creating storm surges as mentioned in the syllabus. The reason explains the mechanism behind storm surges, which aligns with the assertion. Hence, both are true, and the reason correctly explains the assertion.

Key Concept: Impact of cyclones on land

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that cyclones cause extensive flooding in coastal areas due to storm surges, which is true because cyclones generate strong winds that push seawater inland, leading to flooding. The reason explains that storm surges occur when strong winds push seawater towards the shore, forming a wall of water that floods coastal areas. Both the assertion and reason are correct, and the reason accurately explains why cyclones lead to flooding through storm surges.

Key Concept: Impact of Cyclones on Agriculture

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that cyclones cause long-term agricultural damage due to seawater contamination, which is true as cyclones often bring storm surges that flood coastal regions. The reason states that salt from seawater reduces soil fertility, which is also true and directly explains why the assertion is correct since saline water adversely affects crops and soil quality.

Key Concept: Eye of the cyclone

b) Low pressure and calm winds
[Solution Description]
The eye of a cyclone is the region of lowest pressure at the center, where winds are calm, while the surrounding regions experience strong winds and heavy rainfall.

Key Concept: Measures to monitor and predict cyclones

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that weather satellites are essential for accurately predicting the path of a cyclone, which is true because they help in tracking the movement and intensity of cyclones. The reason given is that satellites provide real-time data on atmospheric conditions, which is also true since this data is crucial for monitoring cyclones. Moreover, the reason correctly explains why satellites are essential for prediction, as their data allows meteorologists to make accurate forecasts. Therefore, both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Key Concept: Cyclone Monitoring

b) Weather monitoring satellites
[Solution Description]
Weather monitoring satellites provide real-time data on cloud patterns, wind speeds, and pressure systems, enabling accurate tracking and prediction of cyclone paths. Doppler radar and weather stations also contribute, but satellites offer the most comprehensive coverage.

Key Concept: Assertion-Reason

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The Assertion states that the IMD issues alerts and warnings for cyclones, which is true as per the syllabus. The Reason states that weather monitoring satellites help track cyclones and predict their path, which is also true as mentioned in the syllabus. The Reason correctly explains why the IMD can issue alerts and warnings because satellite data is crucial for cyclone prediction and tracking. Hence, both Assertion and Reason are true, and the Reason is the correct explanation of the Assertion.