Key Concept: Algebra

c) 4

[Solution Description]

To solve for $x$, we subtract 3 from both sides of the equation:

$x + 3 - 3 = 7 - 3$

Simplifying this, we get:

$x = 4$

Therefore, the value of $x$ is 4.

Key Concept: Types of Charges, Interaction of Charges

b) Negative charge

[Solution Description]

According to the convention, a glass rod acquires a positive charge when rubbed with silk. For the charged plastic straw to attract the positively charged glass rod, it must carry the opposite charge. Since like charges repel and unlike charges attract, the plastic straw must carry a negative charge.

Key Concept: Lightning, Static Electricity

d) The balloon will move towards the metal object but not stick

[Solution Description]

When a balloon is rubbed against hair, it becomes negatively charged due to the transfer of electrons from the hair to the balloon. When this charged balloon is brought close to a metal object, the free electrons in the metal will be repelled by the negative charge on the balloon, causing a redistribution of charges in the metal. This results in the metal object becoming positively charged on the side closest to the balloon and negatively charged on the opposite side. Due to the attraction between the negatively charged balloon and the positive charges on the metal, the balloon will move towards the metal object.

Key Concept: Earthquake, Richter scale

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that earthquakes with magnitudes above 7 on the Richter scale are destructive and can cause significant damage. This is a factual statement supported by scientific understanding of earthquakes. The Richter scale quantifies the energy released during an earthquake, and it is well-documented that earthquakes with magnitudes higher than 7 are highly destructive. The reason explains that the Richter scale measures the energy released by an earthquake, and higher magnitudes correspond to greater energy release, which directly leads to increased destruction. Thus, the reason correctly explains the assertion. Therefore, both the assertion and reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Lightning

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion is true because lightning is indeed caused by the accumulation of charges in the clouds. The reason is also true as the process of electric discharge between clouds and the earth produces lightning. Moreover, the reason correctly explains the assertion since the accumulation of charges leads to electric discharge, which is what lightning is.

Key Concept: Electric Charges

c) Lightning is essentially the same as electric sparks from clothes

[Solution Description]

In 1752, Benjamin Franklin demonstrated that lightning is essentially the same phenomenon as the electric sparks observed when removing certain types of clothing. This showed that lightning is a form of electrical discharge.

Key Concept: Precautions to minimize destruction

c) Find a clear spot and drop to the ground

[Solution Description]

If you are outdoors during an earthquake, you should find a clear spot away from buildings, trees, and overhead power lines. Drop to the ground to protect yourself from falling debris.

Key Concept: Structural safety, Earthquake precautions

b) Fix them to the walls[Solution Description]In earthquake-prone areas, cupboards and shelves should be fixed to the walls to prevent them from falling easily during an earthquake. This reduces the risk of injury from falling objects.

Key Concept: Lightning Conductor

c) To provide a safe route for electric charge to the ground[Solution Description]A lightning conductor is installed to protect buildings from the effects of lightning by providing an easy route for the transfer of electric charge to the ground.

Key Concept: Lightning, Electric Discharge

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 accumulation of charges in the clouds, which is a correct statement based on the syllabus. The reason explains that the separation of charges in clouds is caused by the upward movement of air currents and downward movement of water droplets, which is also accurate. However, while both statements are true, the reason does not directly explain why the accumulation of charges leads to lightning. Instead, the reason describes the process of charge separation. Therefore, the reason is not the correct explanation of the assertion.

Key Concept: Ancient Knowledge

c) Benjamin Franklin

[Solution Description]

Benjamin Franklin, an American scientist, showed in 1752 that lightning and the spark from clothes are essentially the same phenomena. This discovery helped humanity understand the nature of lightning better.

Key Concept: Electric Charges, Discharging

c) The object loses its excess charge to the earth.

[Solution Description]

When a charged object is grounded, it loses its excess electric charge to the earth through the grounding process. This occurs because the earth acts as a reservoir for electric charges, allowing the object to neutralize its charge. For example, if you touch a charged foil strip with your hand, the strip discharges as the charge flows through your body into the ground.

Key Concept: Earthing

a) Earthing

[Solution Description]

The process of transferring charge from a charged object to the earth is known as earthing.

Key Concept: Lightning - Historical Background

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that in ancient times, people believed that lightning was a sign of the wrath of gods. This is true as per the syllabus, which mentions that people were afraid of lightning and attributed it to divine anger. The reason given is that they did not understand the scientific cause of lightning and thought it was a supernatural phenomenon. This is also true because the syllabus explains that ancient people lacked knowledge about the accumulation of charges in clouds, which we now know causes lightning. Furthermore, the reason correctly explains the assertion, as the lack of scientific understanding led to the belief in divine intervention. Therefore, both the assertion and reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Ancient observations, Modern understanding

d) The Greeks' work on amber led to the understanding of electrical charges.

[Solution Description]

The ancient Greeks noticed that rubbed amber attracted light objects, which was an early observation of static electricity. This laid the foundation for later scientists like Benjamin Franklin to connect this phenomenon to lightning, leading to the modern understanding of electrical charges in clouds as the cause of lightning.

Key Concept: Ancient beliefs about lightning

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that in ancient times, people believed that lightning was caused by the wrath of gods. This is true as per the syllabus, which mentions that ancient people did not understand the cause of lightning and thought it was a sign of divine anger. The reason given is that they did not understand the scientific cause of lightning and were afraid of it. This is also true and directly explains why they attributed lightning to the wrath of gods. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Benjamin Franklin’s experiment

c) Lightning and the spark from clothes are essentially the same phenomena

[Solution Description]

Benjamin Franklin proved that lightning and the spark from clothes are essentially the same phenomena. This was a significant discovery that connected natural electrical phenomena with everyday experiences.

Key Concept: Electric Charge

c) Negative charge

[Solution Description]

When amber is rubbed with fur, electrons are transferred from the fur to the amber, giving the amber a negative charge.

Key Concept: Electric Discharge, Lightning

d) $3 \times 10^9 \text{ V}$

[Solution Description]

The minimum potential difference $V$ required for lightning to occur can be calculated using the formula:

$V = E \times d$

where $E$ is the electric field strength and $d$ is the distance. Given $E = 3 \times 10^6 \text{ V/m}$ and $d = 1000 \text{ m}$:

$V = 3 \times 10^6 \text{ V/m} \times 1000 \text{ m} = 3 \times 10^9 \text{ V}$

Therefore, the minimum potential difference needed for lightning to occur is $3 \times 10^9 \text{ V}$.

Key Concept: Charge Accumulation

b) Near the upper edges of the clouds

[Solution Description]

According to the syllabus, during the development of a thunderstorm, positive charges collect near the upper edges of the clouds due to the vigorous movement of air currents and water droplets.

Key Concept: Charge Transfer, Electric Discharge

c) An electric discharge occurs, producing lightning

[Solution Description]

When the magnitude of the accumulated charges becomes very large, the air, which is normally a poor conductor of electricity, can no longer resist the flow of charges. This leads to an electric discharge where the negative and positive charges meet, producing streaks of bright light and sound, which we observe as lightning.

Key Concept: Earthing, Charge Transfer

c) To provide a path for excess current to flow into the earth

[Solution Description]

Earthing provides a safe path for the leakage of electrical current to the earth, preventing it from passing through a person or causing damage to electrical appliances. This protects individuals from electrical shocks and ensures the safety of the electrical system.

Key Concept: Charge separation, electric discharge

c) Air currents move upward and water droplets move downward

[Solution Description]

During a thunderstorm, air currents move upward while water droplets move downward. This vigorous movement causes the separation of charges. Positive charges collect near the upper edges of the clouds, and negative charges accumulate near the lower edges. When the accumulation becomes large enough, the air can no longer resist the flow of charges, leading to an electric discharge, which we see as lightning.

Key Concept: Accumulation of charges, electric discharge

c) The separation of charges due to movement of air and water droplets

[Solution Description]

The primary reason for the accumulation of charges near the edges of clouds during a thunderstorm is the separation of charges caused by the vigorous movement of air currents and water droplets. Positive charges collect near the upper edges of the clouds, while negative charges accumulate near the lower edges. This accumulation eventually leads to an electric discharge when the charges become too large for the air to resist.

Key Concept: Charging by Rubbing

b) Polythene

[Solution Description]

A plastic refill can be charged by rubbing it with materials like polythene or woollen cloth. These materials facilitate the transfer of electrons, causing the refill to become charged.

Key Concept: Charging by Rubbing

c) The paper attracts the scale

[Solution Description]

When a plastic scale is rubbed on dry hair, it acquires an electric charge. This charged scale can attract very small pieces of paper due to electrostatic forces.

Key Concept: Charging by Rubbing, Types of Materials

c) The mustard seeds will be attracted to the balloon.

[Solution Description]

When a balloon is rubbed with dry hair, it acquires a charge due to the transfer of electrons. This charged balloon will exert an electrostatic force on small, light objects like mustard seeds, causing them to be attracted to the balloon. This attraction occurs because the charged balloon induces a temporary opposite charge in the mustard seeds.

Key Concept: Charging by Rubbing, Electric Charge

d) Assertion is false, but Reason is true.

[Solution Description]

When a plastic refill is rubbed with polythene, electrons are transferred from the refill to the polythene because polythene has a higher electron affinity. This transfer of electrons causes the plastic refill to become positively charged and the polythene to become negatively charged. However, the assertion states that the refill acquires a negative charge, which is incorrect. The reason provided correctly explains why the refill acquires a positive charge. Therefore, the Assertion is false, but the Reason is true.

Key Concept: Charging by Rubbing

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

When a plastic comb is rubbed with dry hair, electrons are transferred from the hair to the comb, causing the comb to become negatively charged. This charge allows the comb to attract small pieces of paper, which are neutral or have a slight opposite charge. Therefore, the assertion is true. The reason provided explains that the rubbing process transfers electrons, which is correct and directly explains why the comb becomes charged. Hence, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Charging by Rubbing

b) Polythene[Solution Description]According to the syllabus, a plastic refill can be charged by rubbing it with polythene or woollen cloth.

Key Concept: Types of Charges

b) Negative charge

[Solution Description]

When a glass rod is rubbed with silk, it acquires a positive charge. Conversely, when a plastic straw is rubbed with polythene, it acquires a negative charge. This is based on the convention that the charge acquired by a glass rod rubbed with silk is positive, and the other kind of charge (acquired by a plastic straw rubbed with polythene) is negative.

Key Concept: Interaction of Charges

b) The balloon and refill have opposite types of charge

[Solution Description]

From the activity, it is observed that a charged balloon attracts a charged refill. This indicates that the balloon and the refill carry opposite types of charges. According to the convention, the charge on a glass rod rubbed with silk is positive, and the charge on a plastic straw rubbed with polythene is negative. Therefore, if the balloon and the refill attract each other, they must have opposite charges.

Key Concept: Like charges repel, unlike charges attract, Charge Transfer

b) The glass rod has a positive charge and the straw has a negative charge.

[Solution Description]

According to the convention, when a glass rod is rubbed with silk, it acquires a positive charge. When a plastic straw is rubbed with polythene, it acquires a negative charge. Since unlike charges attract each other, the plastic straw (negatively charged) is attracted to the glass rod (positively charged).

Key Concept: Like charges repel, unlike charges attract, Interaction of Charges

b) The balloons have the same type of charge.

[Solution Description]

When two balloons are rubbed with a woollen cloth, they acquire the same type of charge. According to the principle that like charges repel each other, the balloons move away from each other. This indicates that both balloons have the same type of charge.

Key Concept: Charges, Interaction, Types of Charges

b) The balloon and refill will attract each other.

[Solution Description]

When a refill is rubbed with polythene, it acquires a negative charge. A charged balloon (which acquires a positive charge when rubbed with a woollen cloth) will attract the negatively charged refill. This is because unlike charges attract each other. Therefore, the most likely observation is that the balloon and the refill will attract each other.

Key Concept: Interaction of Like Charges

b) They repel each other

[Solution Description]

When two balloons are rubbed with a woollen cloth, they acquire the same type of charge. According to the principle of electrostatics, like charges repel each other. Therefore, when two charged balloons are brought close to each other, they will repel each other.

Key Concept: Electroscope and Charge Transfer

c) The foil strips diverge further

[Solution Description]

When a charged object is touched to the paper clip of the electroscope, the charge is transferred from the object to the aluminum foil strips through the metal paper clip. Since both strips receive the same type of charge, they repel each other and diverge further.

Key Concept: Earthing

b) Earthing

[Solution Description]

The process of transferring charge from a charged object to the earth is called earthing. This helps in discharging the object and making it neutral.

Key Concept: Detection of Charge

c) Electroscope

[Solution Description] An electroscope is a device used to detect whether an object is charged or not. When a charged object touches the electroscope, the aluminium foil strips inside it repel each other due to the transfer of like charges.

Key Concept: Electroscope Function

b) To detect the presence of charge

[Solution Description]

The primary function of an electroscope is to detect whether an object is charged or not. When a charged object is brought near the metal clip, the aluminum foil strips repel each other due to the transfer of the same charge, indicating the presence of charge.

Key Concept: Electroscope, Charge Detection

c) They will repel each other and move apart

[Solution Description]

When a positively charged body is touched with the paper clip of an uncharged electroscope, the positive charge is transferred to the electroscope through the metal conductor (paper clip). The aluminium foil strips receive the same positive charge and repel each other due to like charges. Thus, the foil strips will diverge or open up.

Key Concept: Concept: Detecting Charge

c) Electroscope

[Solution Description]

An electroscope can be used to detect whether an object is carrying charge or not. When a charged object touches the electroscope, the aluminium foil strips repel each other, indicating the presence of charge.

Key Concept: Earthing

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The foil strips collapse when touched with a hand because the charge on the strips flows through the body to the earth, a process known as earthing. The assertion that a charged object loses its charge to the earth when earthed is true as earthing facilitates the transfer of charge from the object to the earth. The reason given is also correct because earthing indeed provides a conductive path for the charge to flow, leading to the discharge of the object. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Earthing, Charge Transfer

c) The charge on the metal sphere decreases and eventually becomes neutral

[Solution Description]

When a charged metal sphere is connected to the earth through a conducting wire, the excess charge on the sphere flows to the earth. This process is called earthing. The charge on the metal sphere decreases until it becomes neutral, i.e., it loses all its excess charge.

Key Concept: Electroscope

b) The strips repel each other

[Solution Description]

When a charged object is touched to the paper clip of an electroscope, the charge is transferred to the aluminium foil strips through the paper clip. Since metals are good conductors, both strips receive the same charge. Similar charges repel each other, causing the foil strips to move apart and become wide open.

Key Concept: Earthing

c) The strips lose charge to the earth through the body

[Solution Description]

When the paper clip is touched with a hand, the charge on the aluminium foil strips is transferred to the earth through the body. This process is called earthing. As a result, the strips lose their charge and return to their original state, collapsing back together.

Key Concept: Charge Transfer, Earthing

c) The sphere loses all its positive charges and becomes neutral

[Solution Description] When a positively charged metal sphere is connected to the ground via a conducting wire, the excess positive charges on the sphere flow through the wire to the earth. This process continues until the sphere becomes neutral, meaning it has no net charge. The grounding wire provides a path for the charges to move from the sphere to the earth, equalizing the potential between them.

Key Concept: Discharging

c) The object loses its charge

[Solution Description]

When a charged object is touched by a human hand, the charge is transferred to the earth through the body. This process is known as discharging, and it causes the object to lose its charge.

Key Concept: Electric Discharge

b) Electric discharge

[Solution Description]

When negative and positive charges meet, they produce streaks of bright light and sound. This process is known as electric discharge.

Key Concept: Electric Discharge

c) Negative and positive charges meet, causing lightning

[Solution Description]

When the magnitude of accumulated charges in the clouds becomes very large, the air, which is normally a poor conductor of electricity, can no longer resist the flow of these charges. As a result, negative and positive charges meet, producing streaks of bright light and sound. This process is known as an electric discharge, and it is what we perceive as lightning.

Key Concept: Lightning, Electric Discharge

d) Electric charge from lightning can travel through wired connections.

[Solution Description] Lightning can strike telephone cords, electrical wires, and metal pipes. When lightning strikes, the electric charge can travel through these conductors, posing a risk to anyone using wired devices. Mobile phones, being wireless, do not have this risk as they are not connected to any physical conductors that can carry the electric charge from a lightning strike.

Key Concept: Lightning Safety

b) Staying inside a car with windows closed[Solution Description]During a thunderstorm, it is safe to stay inside a house or a building with windows and doors shut. Open vehicles, open fields, tall trees, and elevated places are not safe.

Key Concept: Electric Discharge

a) Lightning is formed

[Solution Description]

When negative and positive charges meet during a thunderstorm, it results in an electric discharge. This discharge produces streaks of bright light, which we see as lightning, along with sound.

Key Concept: Historical Understanding

c) Greeks

[Solution Description]

The ancient Greeks knew as early as 600 B.C. that rubbing amber with fur attracted light objects like hair, which is an early observation related to electricity.

Key Concept: Electric Discharge

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

According to the syllabus, during the development of a thunderstorm, the air currents move upward while the water droplets move downward, causing the separation of charges. Positive charges collect near the upper edges of the clouds, and negative charges accumulate near the lower edges. When the magnitude of these charges becomes very large, the air can no longer resist their flow, leading to an electric discharge, which we observe as lightning. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Charge Separation, Electric Discharge

c) The magnitude of accumulated charges exceeds air's resistance

[Solution Description]

The primary reason for electric discharge during a thunderstorm is the inability of air, which is normally a poor conductor of electricity, to resist the flow of accumulated charges when their magnitude becomes very large. This causes the negative and positive charges to meet, resulting in lightning.

Key Concept: Lightning conductor, Earthing

b) By providing a safe path for the electric charge to the ground

[Solution Description]

A lightning conductor is a metallic rod installed on buildings that is taller than the structure. One end of the rod is exposed to the air, and the other is buried deep in the ground. When lightning strikes, the conductor provides a low-resistance path for the electric charge to travel safely into the ground, preventing damage to the building.

Key Concept: Electric discharge, Lightning safety

c) To minimize the risk of electric shock and damage

[Solution Description]

During a thunderstorm, lightning can cause a sudden surge of electrical current through power lines. This surge can travel into homes and damage electrical appliances connected to the mains. Even if the appliances are turned off, they can still be affected by the surge. Hence, it is safer to unplug them to prevent any potential damage or risk of electric shock.

Key Concept: Lightning Conductors

b) To provide an easy route for electric charge to the ground

[Solution Description]

A lightning conductor is a device used to protect buildings from the effects of lightning. It provides an easy route for the transfer of electric charge to the ground, thereby protecting the building from damage.

Key Concept: Do’s and Don’ts during a Thunderstorm

b) Taking a shower

[Solution Description]

During a thunderstorm, it is important to avoid contact with telephone cords, electrical wires, and metal pipes as lightning can strike these objects. Bathing should also be avoided to prevent contact with running water. Using mobile phones and cordless phones is safer.

Key Concept: Safe Locations During Thunderstorm

c) Inside a car with windows and doors shut

[Solution Description]

The safest place during a thunderstorm is inside a house or building with all windows and doors closed. It is important to avoid contact with electrical wires, metal pipes, and running water.

Key Concept: Finding a Safe Place, Vehicle Safety

c) Keeping all windows and doors shut[Solution Description]When traveling during a thunderstorm, it is safest to remain inside the vehicle with all windows and doors closed. This provides protection from lightning strikes as the metal body of the vehicle conducts electricity around the passengers, keeping them safe.

Key Concept: Lightning Safety, Precautions during thunderstorms

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that using mobile phones during a thunderstorm is safe inside a house. This is true because mobile phones operate wirelessly and do not have physical electrical connections that can conduct lightning. The reason provided is also correct as it explains that mobile phones lack electrical wires, which are the primary conductors of lightning. Therefore, the reason correctly explains why the assertion is true.

Key Concept: Lightning Safety, Do’s and Don’ts during a Thunderstorm

c) Squat low on the ground

[Solution Description]

If you are in an open field during a thunderstorm with no shelter available, the safest action is to squat low on the ground. This position makes you the smallest target for lightning. You should place your hands on your knees with your head between the hands. Lying flat on the ground increases the risk of being struck by lightning as it maximizes your contact with the ground, making you a larger target. Staying close to tall objects like trees or poles is also dangerous because they are more likely to be struck by lightning.

Key Concept: Lightning Conductors, Electric Charge Transfer

c) The conductor will fail to transfer the electric charge efficiently

[Solution Description]

The lightning conductor works by providing a low-resistance path for the electric charge from lightning to safely reach the ground. If the conductor is replaced with a material of higher resistance, it will not be able to efficiently transfer the electric charge to the ground. This could cause the charge to find alternative paths, potentially damaging the building or causing harm to its occupants.

Key Concept: Lightning Conductors

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that lightning conductors provide a path of least resistance for lightning to reach the ground, which is true. Lightning conductors are designed to divert the electrical discharge from the building into the ground safely. The reason explains that the metallic rod is buried deep in the ground to ensure safe dissipation of electric charge, which is also true. The reason correctly explains why the lightning conductor works, as grounding the rod ensures that the electric charge is safely dissipated into the earth. Therefore, both the assertion and reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Lightning Conductors

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that lightning conductors protect buildings by providing an easy path for electric charge to the ground, which is true. The reason explains that the metallic rod is taller than the building and buried deep in the ground, ensuring efficient transfer of charge, which is also true. Furthermore, the reason correctly explains why the lightning conductor works as described in the assertion.

Key Concept: Electric Discharge

c) The magnitude of accumulated charges becomes very large

[Solution Description]

The air becomes unable to resist the flow of electricity when the magnitude of accumulated charges becomes very large. This leads to an electric discharge, resulting in lightning.

Key Concept: Lightning Conductors, Safety Measures

b) It diverts the lightning strike away from the building.

[Solution Description]

The lightning conductor provides an easy and direct path for the electric charge from the lightning strike to travel safely to the ground. This prevents the charge from passing through the building, thereby protecting it from damage. The metallic rod of the conductor is taller than the building, ensuring it intercepts the lightning strike before it can reach the structure. The other end of the rod is buried deep in the ground to ensure efficient dissipation of the electric charge.

Key Concept: Lightning Safety, Protection Measures

d) Squat low on the ground with head between hands.[Solution Description]In an open field during a thunderstorm, the safest action is to squat low on the ground, placing your hands on your knees with your head between your hands. This position minimizes your height and reduces the risk of being struck by lightning. Lying flat on the ground is not recommended as it increases the surface area exposed to potential lightning strikes. Seeking shelter under tall trees or carrying an umbrella are both dangerous as they increase the risk of being struck.

Key Concept: Lightning Safety, Safe Position

c) Squat low with hands on knees

[Solution Description]

The safest position during a thunderstorm in an open field is to squat low on the ground, placing your hands on your knees with your head between your hands. This position minimizes your height and reduces your chances of being struck by lightning. Lying flat on the ground increases the risk as it maximizes your surface area exposed to the electric discharge.

Key Concept: Lightning Safety, Do’s and Don’ts

b) Take a shower

[Solution Description]

During a thunderstorm, it is unsafe to bathe or use wired phones as lightning can strike through water pipes and telephone cords. Using mobile phones and keeping electrical lights on are safe practices. Unplugging electrical appliances like computers and TVs is also recommended to avoid any potential damage from electrical surges.

Key Concept: Safe Position During Lightning

c) Squat low on the ground with hands on knees

[Solution Description]

According to the syllabus, if no shelter is available during a thunderstorm and you are in an open field, you should squat low on the ground. Place your hands on your knees with your head between the hands. This position makes you the smallest target to be struck by lightning.

Key Concept: Do’s and Don’ts during a Thunderstorm

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that staying inside a car with windows and doors shut is safer during a thunderstorm. This is true because a car provides a metal enclosure that can act as a Faraday cage, which shields the inside from electrical discharges like lightning. The reason given is that a car acts as a Faraday cage and protects occupants from lightning. This is also true because a Faraday cage distributes electric charge around its exterior, preventing it from penetrating the interior. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Do’s and Don’ts During Thunderstorms

c) Squat low on the ground with hands on knees and head between hands

[Solution Description]

If no shelter is available during a thunderstorm, the recommended position is to squat low on the ground, placing your hands on your knees with your head between your hands. This position makes you the smallest target for lightning and reduces the risk of being struck.

Key Concept: Lightning Safety, Safe Position, Open Fields

c) Squat low on the ground with hands on knees and head between hands

[Solution Description]

According to lightning safety guidelines, if no shelter is available in an open field, one should squat low on the ground, place hands on knees, and keep the head between the hands. This position minimizes the risk of being struck by lightning by making the person the smallest possible target.

Key Concept: Lightning Safety, Electrical Appliances

c) Taking a shower

[Solution Description]

To solve this question, we need to understand the risk factors associated with lightning strikes during thunderstorms. Bathing involves contact with running water, which can conduct electricity if lightning strikes plumbing. Using wired phones can also be risky because telephone cords can carry electrical discharges from lightning. However, unplugging electrical appliances reduces the risk of damage but does not directly pose a personal injury risk. Therefore, bathing during a thunderstorm is the most dangerous action among the options.

Key Concept: Lightning Safety, Electrical Appliances

b) Computer

[Solution Description]

During a thunderstorm, lightning can cause power surges that can damage sensitive electronic devices. Computers and TVs are particularly vulnerable to such surges. While electrical lights can remain on without causing harm, it is safer to unplug computers and TVs to protect them from potential damage caused by lightning-induced power surges.

Key Concept: Earthquake Causes

a) Movement of tectonic plates

[Solution Description]

Most earthquakes are caused by the movement of tectonic plates. When these plates brush past one another or collide, they cause disturbances in the earth's crust, leading to earthquakes.

Key Concept: Earthquake Causes

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The outermost layer of the earth is fragmented into tectonic plates, which are in continual motion. When these plates brush past one another or collide, they cause disturbances in the earth's crust. These disturbances manifest as earthquakes on the surface of the earth. Therefore, earthquakes are more likely to occur at the boundaries of tectonic plates, which are also known as seismic or fault zones. Both the Assertion and Reason are true, and the Reason correctly explains the Assertion.

Key Concept: Earthquake Causes, Plate Tectonics

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that earthquakes are primarily caused by the movement of tectonic plates, which is accurate according to the syllabus. The reason explains that the boundaries of tectonic plates are weak zones where stress accumulates, leading to earthquakes. This is also true and directly explains why the movement of plates causes earthquakes. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Weak Zones

a) Boundaries of tectonic plates

[Solution Description]

Earthquakes are more likely to occur at the boundaries of tectonic plates, known as weak zones or seismic zones. Examples include regions like Kashmir, Western and Central Himalayas, and the Indo-Gangetic Plane.

Key Concept: Earthquake Definition

b) A sudden shaking or trembling of the earth

[Solution Description]

An earthquake is a sudden shaking or trembling of the earth which lasts for a very short time. It is caused by a disturbance deep inside the earth's crust.

Key Concept: Plate Movement, Fault Zones

d) Two plates colliding, causing one to subduct

[Solution Description]

Earthquakes are primarily caused by the movement of tectonic plates. When two plates collide, one plate may slide under the other, causing a disturbance in the earth’s crust. This disturbance leads to an earthquake. Among the given options, a collision between two tectonic plates is the most likely cause of a significant earthquake. Volcanic eruptions and meteor impacts can also cause tremors but are less common compared to plate movements.

Key Concept: Measurement of Earthquake

c) Richter scale

[Solution Description]

The power of an earthquake is measured on the Richter scale. This scale quantifies the magnitude of an earthquake, with higher values indicating more destructive energy.

Key Concept: Definition of Earthquake

b) A sudden shaking or trembling of the earth

[Solution Description]

An earthquake is defined as a sudden shaking or trembling of the earth caused by a disturbance deep inside the earth's crust. It lasts for a very short time and can cause significant damage to life and property.

Key Concept: Earthquake causes, Plate movements

d) Kashmir

[Solution Description]

Earthquakes are most likely to occur at the boundaries of tectonic plates, known as fault zones. Among the given options, Kashmir is located in a seismically active region near the boundary of the Indian and Eurasian plates, making it a high-risk area for earthquakes.

Key Concept: Tectonic plate boundaries, Seismic waves

d) Primary (P) waves

[Solution Description]

When an earthquake occurs at a subduction zone, the first waves to be detected by a seismograph are Primary (P) waves. P-waves are compressional waves that travel faster than other seismic waves and are the first to arrive at any given location after an earthquake.

Key Concept: Richter Scale

c) 1000 times more energy

[Solution Description]

An increase of 2 in magnitude on the Richter scale indicates that the destructive energy of the earthquake has increased by 1000 times. For example, an earthquake of magnitude 6 has 1000 times more destructive energy than an earthquake of magnitude 4.

Key Concept: Quake-Safe Construction

c) Mud

[Solution Description]

The syllabus suggests that in highly seismic areas, the use of mud or timber is better than using heavy construction materials to minimize damage in case of an earthquake.

Key Concept: Earthquakes, Landslides, Tsunamis

c) Earthquake, Tsunami, Landslide

[Solution Description] An underwater earthquake near the coast can generate a tsunami due to the displacement of water. Additionally, the shaking from the earthquake can trigger landslides on the nearby land. The correct sequence is earthquake, followed by tsunami, and then landslide.

Key Concept: Destructive Energy

c) 1000 times

[Solution Description]

According to the Richter scale, an increase of 2 in magnitude means 1000 times more destructive energy. Therefore, an earthquake of magnitude 6 has 1000 times more destructive energy than an earthquake of magnitude 4.

Key Concept: Richter Scale

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The Richter scale is a logarithmic scale used to measure the magnitude of earthquakes. According to the syllabus, an increase of 2 in magnitude on the Richter scale corresponds to a 1000-fold increase in destructive energy. Therefore, an earthquake of magnitude 8 indeed has 1000 times more destructive energy than an earthquake of magnitude 6. The reason correctly explains the assertion as it provides the scientific basis for the relationship between magnitude and destructive energy on the Richter scale.

Key Concept: Epicenter, Seismic waves

b) It is the point on the Earth's surface directly above the focus

[Solution Description]

The epicenter is the point on the Earth's surface directly above the focus (the point inside the Earth where the earthquake originates). It is where the seismic waves start to radiate outward.

Key Concept: Earthquake-Prone Areas in India

c) Assertion is true, but Reason is false.

[Solution Description]

The Assertion states that the Indo–Gangetic Plain is one of the most earthquake-prone areas in India, which is true as per the syllabus. However, the Reason given is that the Indo–Gangetic Plain lies at the boundary of two tectonic plates, which is false. The Indo–Gangetic Plain is not located at a plate boundary but is considered a seismic zone due to its proximity to the Himalayas, which are at a plate boundary. Therefore, the Assertion is true, but the Reason is false.

Key Concept: Seismic Zones, Geographic Location

c) Proximity to tectonic plate boundaries[Solution Description]The primary factor that determines the classification of an area as a seismic zone is its proximity to the boundaries of tectonic plates. Earthquakes are more likely to occur near these boundaries due to the movement and interaction of the plates. Other factors like temperature, humidity, or altitude do not directly contribute to the classification of seismic zones.

Key Concept: Earthquake-prone states in India

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The syllabus mentions that the boundaries of tectonic plates are the weak zones where earthquakes are more likely to occur. These weak zones are also known as seismic or fault zones. In India, Jammu and Kashmir is one of the areas most threatened by earthquakes because it falls under these weak zones. Therefore, both the Assertion and the Reason are true, and the Reason correctly explains why Jammu and Kashmir is prone to earthquakes.

Key Concept: Earthquake Protection

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that in highly seismic areas, it is better to use mud or timber for construction, which is true as per the syllabus. The reason provided is that mud and timber are lighter materials and cause less damage if the structure collapses, which is also true. Furthermore, the reason correctly explains why using mud or timber is advisable in seismic zones. Therefore, both the assertion and reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Earthquake-Resistant Materials

c) Mud

[Solution Description]

In highly seismic areas, the use of lightweight materials like mud or timber is better than using heavy construction materials. This helps in reducing the damage caused by earthquakes as lighter materials are less likely to cause severe harm if the structure collapses.

Key Concept: Precautionary Measures Outdoors

a) Find a clear spot, away from buildings and trees, and drop to the ground[Solution Description]The syllabus suggests that if you are outdoors during an earthquake, you should find a clear spot away from buildings, trees, and overhead power lines. You should drop to the ground and stay there until the tremors stop. This minimizes the risk of injury from falling debris.