Ans. Electric charge is a fundamental property of matter due to which it experiences a force in the presence of other charged bodies. There are two types of electric charges: positive charge and negative charge. Normally, any object has equal numbers of positively charged protons and negatively charged electrons, so it is electrically neutral. An object becomes charged when there is a transfer of electrons. If an object loses electrons, it has more protons than electrons and becomes positively charged. If an object gains extra electrons, it has more electrons than protons and becomes negatively charged. The imbalance of charges on an object is what we refer to as electric charge.

Ans. Charging by rubbing is also called frictional charging. When two objects are rubbed against each other, electrons may be transferred from one object to the other. For example, when a plastic scale is rubbed with dry hair, the scale gains electrons from the hair and becomes negatively charged, while the hair loses electrons and becomes positively charged. The charges produced in this way remain at rest on the surface of the objects and do not move freely, so they are called static charges. This is why the effect is known as static electricity. The attraction of small paper bits by the charged scale is a common classroom demonstration of this process.

Ans. The basic rule of interaction between charges is: like charges repel each other and unlike charges attract each other. This can be shown by the following activities:

• Activity 1: Charge two balloons by rubbing them with a woollen cloth. When they are brought close, they push each other away. Both balloons carry similar (negative) charges, so they repel each other.
• Activity 2: Charge a glass rod by rubbing it with silk (positive charge) and a plastic rod by rubbing it with wool (negative charge). When both rods are brought near each other, they attract. This shows that unlike charges attract.

These simple experiments support the rule of attraction and repulsion of electric charges.

Ans. Static electricity is the electric charge that remains at rest on the surface of an object. It is produced when charges are transferred between objects and then stay on them instead of flowing. Some everyday situations where we observe static electricity are:

• When we rub a plastic comb or scale through dry hair, it starts attracting small bits of paper.
• When we remove a woollen sweater in a dark room, we sometimes see tiny sparks and hear a crackling sound.
• When we get down from a car or slide off a plastic chair, we may feel a mild electric shock due to discharge of static charges.

These examples show the presence of static charges that are produced by friction and then suddenly discharged.

Ans. Static electricity is more easily observed in dry weather because the air contains very little moisture. In dry air, static charges produced on objects cannot leak away quickly and remain on the surface for a longer time. Their effects, such as attraction of small pieces of paper or small sparks, are therefore clearly visible. In humid weather, air contains more water vapour. Moisture present in the air provides a conducting path for the charges to move away slowly from the surface of objects. As a result, static charges do not build up in large amounts and their effects are weaker, so we cannot observe static electricity easily on a humid day.

Ans. A simple electroscope consists of a glass jar with a cork or rubber stopper at its mouth. A metal rod passes through the stopper. At the top end of the rod, there is a metal knob or disc, and at the lower end, two thin metal leaves (usually aluminium foil) are attached. When a charged object is brought in contact with the metal knob, the charge spreads through the rod to both the leaves. Since both leaves get the same type of charge, they repel each other and move apart. The spreading of the leaves indicates that the object is charged. Thus, an electroscope helps in detecting the presence of electric charge on a body.

Ans. To test whether a given object is charged using an electroscope, we follow these steps:

1. First, ensure that the electroscope leaves are close together, showing it is uncharged or neutral.
2. Take the object to be tested (for example, a plastic scale) and bring it near the metal knob without touching it. If there is no movement of the leaves, the object may be uncharged or weakly charged.
3. Now gently touch the metal knob with the object. If the object is charged, some charge will be transferred to the electroscope.
4. As the charge spreads to both leaves, they acquire like charges and repel each other, moving apart.

If the leaves diverge after touching the object to the knob, it shows that the object is charged. If there is no change, the object is uncharged.

Ans. When we touch the metal knob of a charged electroscope with our hand, the leaves that were earlier diverged start coming closer and finally collapse. This happens because our body is a good conductor of electricity and is connected to the Earth. As soon as we touch the electroscope, the excess charges on it find a path to flow to the Earth through our body. This process is called earthing. When charges leave the electroscope, the leaves lose their like charges and hence the repulsion between them decreases and disappears. The leaves then come back to their original position, indicating that the electroscope has become neutral.

Ans. To demonstrate transfer of charge, first charge the electroscope so that its leaves diverge. This shows that the electroscope is charged. Now take another uncharged metallic object, such as a metal spoon, and touch it to the metal knob of the charged electroscope. Some of the charge from the electroscope flows to the spoon. As a result, the amount of charge on the leaves decreases and they come closer together. If we now bring the spoon near small bits of paper, we may observe that it can attract them, indicating it has become charged. This activity clearly shows that electric charge can be transferred from one object (electroscope) to another (spoon) through contact.

Ans. A glass jar is used to enclose the leaves of an electroscope for the following reasons:

• Protection from air currents: Thin metal leaves are very light and can move due to air currents. The glass jar prevents external air from disturbing the leaves so that they move only due to electric charges.
• Protection from moisture and dust: Moisture in air and dust particles can provide a path for charges to leak away. The glass jar reduces contact with moist air and dust, helping the leaves to retain charge for a longer time and giving more accurate observations.

Thus, the glass jar ensures reliable performance and protects the delicate leaves of the electroscope.

Ans. Lightning is a sudden and bright flash of light in the sky accompanied by thunder, caused by a massive electric discharge in the atmosphere. During a thunderstorm, strong upward and downward air currents make water droplets and ice particles in clouds collide and rub against each other. Due to this friction, some parts of the cloud become positively charged and some parts become negatively charged. The ground also may acquire a positive charge by induction. When the difference in charges between the clouds, or between a cloud and the Earth, becomes very large, the air, which is usually an insulator, breaks down and becomes a conductor. This results in a sudden flow of charges, called an electric discharge, which we see as lightning.

Ans. The sequence of events during a lightning strike is as follows:

1. Collisions and rubbing between water droplets and ice particles in a cloud cause separation of charges, making some regions positively charged and others negatively charged.
2. The ground below the cloud may become positively charged by induction.
3. As the charge difference grows, the electric field between the cloud and the ground (or between clouds) becomes very strong.
4. At a critical point, the insulating air cannot resist the electric field and breaks down, forming a conducting path.
5. A huge and sudden flow of electric charge occurs along this path. This is seen as a bright flash of lightning.
6. The discharge heats the surrounding air rapidly, causing it to expand and then contract suddenly. This creates shock waves in air, which we hear as thunder.

Thus, lightning and thunder are parts of the same phenomenon of electric discharge in the atmosphere.

Ans. Lightning and thunder are produced at the same time during an electric discharge in the sky. However, we see the lightning flash before we hear the thunder because light travels much faster than sound. Light travels at a speed of about 3 × 10⁸ m/s, whereas sound travels at about 340 m/s in air. Due to this large difference, light from the lightning flash reaches our eyes almost instantly, while sound from thunder takes more time to reach our ears. The greater the distance from the storm, the larger is the time gap between seeing the flash and hearing the thunder.

Ans. Lightning is considered a natural example of discharge of static electricity because it involves a sudden flow of electric charge between regions that were previously charged due to friction in clouds. This is similar to the small sparks we see when we touch a metal object after walking on a carpet. In both cases:

• Charges are first built up (in clouds or on our body) and remain at rest, forming static electricity.
• When the potential difference becomes large enough, the insulating air breaks down and charge flows suddenly, producing a spark.

The main difference is that lightning involves a very large amount of charge and energy, causing a huge flash and loud thunder, whereas a domestic spark is very small and usually harmless. Thus, lightning is a large-scale version of the same principle.

Ans. Lightning can have several harmful effects on life and property:

• It can cause serious injuries or death to humans and animals if it strikes them directly.
• Lightning can burn trees and forests, leading to forest fires and environmental damage.
• It may cause fires in buildings by heating roofing materials or igniting flammable substances.
• Lightning can damage electrical and electronic equipment, including power lines, transformers, and communication systems, leading to power failures and loss of services.

Because of these harmful effects, it is very important to follow safety measures and use protective devices during thunderstorms.

Ans. Important safety precautions indoors during a thunderstorm are:

• Stay away from windows and doors: Lightning can enter through openings and broken glass may cause injury.
• Avoid using wired electrical appliances: Lightning surges can travel through electric wires and damage devices or cause shocks.
• Do not touch metal pipes or taps: Metal conducts electricity, so any charge induced in the building may pass through them.
• Avoid bathing during lightning: Water is a good conductor and lightning currents may travel through water pipes.

Following these precautions reduces the risk of electric shock and injuries caused by lightning inside a building.

Ans. If you are caught in an open field during a thunderstorm, you should immediately look for a safe place such as a nearby building or a car. If no shelter is available, you should squat low on the ground with your feet close together, head down, and hands on your knees. This position reduces your height and the area of contact with the ground, lowering the chance of being struck. You must avoid:

• Standing under a single tall tree or near tall isolated objects like poles or towers.
• Running in open spaces, standing on rooftops, or staying on high ground.
• Carrying metal objects such as umbrellas with metal rods, hockey sticks, or tools.

Avoiding these situations helps protect you from direct lightning strikes.

Ans. A lightning conductor is a device used to protect buildings from lightning strikes. It is usually made of a long metal rod (often copper) fixed at the highest point of the building. The rod extends above the roof and is connected by thick metal strips along the wall to a large metal plate buried deep in the ground. During a thunderstorm, if lightning is about to strike the building, the conductor provides an easier path for the electric discharge. The charge passes through the metal rod and strips to the metal plate and then safely into the Earth instead of passing through the building. In this way, the lightning conductor prevents damage to the structure and reduces the risk of fire and electric shock.

Ans. It is safer to stay inside a closed car during a thunderstorm because the metal body of the car acts like a protective shield. When lightning strikes the car, the electric charges travel along the outer metal surface and then pass to the ground. The interior of the car remains largely unaffected. This phenomenon is known as the Faraday cage effect. As long as the windows are closed and you are not touching the metal parts, the electric current stays on the outside and you remain safe inside. On the other hand, standing outside in the open makes you one of the tallest objects and increases the risk of being struck directly by lightning.

Ans. An earthquake is a sudden shaking or trembling of the Earth’s surface caused by a disturbance deep inside the Earth. The Earth’s outer layer, called the crust, is not a single solid piece. It is broken into large pieces called tectonic plates which float on the semi-molten layer beneath. These plates are constantly moving very slowly. Sometimes, two plates get locked at their edges due to friction and cannot move smoothly. Stress builds up at these locked regions over many years. When the stress becomes very large, the rocks suddenly break or slip, releasing a huge amount of energy. This energy travels in the form of seismic waves causing the ground to shake, which we feel as an earthquake.

Ans. The focus of an earthquake is the point inside the Earth where the earthquake actually originates due to sudden breaking or movement of rocks. The epicentre is the point on the Earth’s surface directly above the focus. The intensity of shaking is usually greatest at or near the epicentre because the seismic waves have travelled the shortest distance from the focus. As we move farther away from the epicentre, the energy of the waves spreads out and decreases, so the shaking felt becomes weaker. Therefore, damage to buildings and structures is generally more severe near the epicentre and less severe at greater distances.

Ans. Seismic waves are waves of energy that travel through the Earth during an earthquake. They are produced when rocks break or slip along faults, releasing stored energy. These waves cause the ground to shake and are responsible for the damage we see on the surface. The instrument used to record seismic waves is called a seismograph. It records the vibrations of the Earth on a rotating drum or digital screen. The magnitude (or strength) of an earthquake is measured on the Richter scale. Higher values on the Richter scale indicate more powerful earthquakes, which can cause greater destruction, especially in populated areas.

Ans. Some regions of the Earth are more prone to earthquakes because they lie along the boundaries of tectonic plates where movement and collision are more frequent. At these plate boundaries, stresses build up easily and are released as earthquakes. In India, the Himalayan region and the areas in the north-eastern states are highly earthquake-prone because the Indian plate is colliding with the Eurasian plate in this region. States like Jammu & Kashmir, Himachal Pradesh, Uttarakhand, Assam, and parts of Bihar and North Bengal fall in high-risk zones. On the other hand, central and southern parts of India are relatively less prone to strong earthquakes as they lie away from active plate boundaries.

Ans. Strong earthquakes can have many harmful effects on human life and the environment:

• Loss of life and injuries: Collapse of buildings, bridges, and structures can kill or injure many people and animals.
• Destruction of property: Houses, roads, railways, and other infrastructure can be severely damaged, resulting in huge economic losses.
• Damage to essential services: Earthquakes can break water pipelines, gas lines, and electric cables, causing fires, flooding, and power failures.
• Environmental changes: They may cause landslides, changes in river courses, formation of cracks in the ground, and sometimes trigger tsunamis in oceans.

Because of these destructive effects, it is important to design earthquake-resistant structures and follow safety rules.

Ans. If an earthquake occurs while you are indoors, you should:

• Stay calm and do not rush outside immediately, as falling objects and debris may injure you.
• Quickly Drop, Cover, and Hold – drop to the ground, take cover under a strong table, desk, or bed, and hold on to it.
• Stay away from windows, glass panes, mirrors, tall furniture, and heavy objects that may fall.
• Do not use lifts; use stairs only after the shaking stops if evacuation is necessary.
• If you are in bed, stay there and protect your head with a pillow instead of running.

These measures help reduce the chances of getting hurt by falling objects and collapsing parts of the building.

Ans. If you are in an open area during an earthquake, the following precautions should be taken:

• Move to an open ground away from buildings, trees, electric poles, streetlights, and overhead wires.
• Do not stand near walls, bridges, flyovers, or under hanging boards, as they may collapse or fall.
• If you are near the seashore and a strong earthquake occurs, move to higher ground immediately to avoid possible tsunamis.
• If you are in a moving vehicle, the driver should stop in an open area and stay inside the vehicle until the tremors stop.

These steps reduce the risk of injury from falling structures or other earthquake-related hazards.

Ans. It is important to construct earthquake-resistant buildings in earthquake-prone areas to minimize damage to property and save human lives during earthquakes. Such buildings are designed to withstand shaking without collapsing. Two features of earthquake-resistant buildings are:

• They use lightweight materials like wood, steel, or reinforced concrete, which reduce the total weight and impact of shaking.
• They have strongly tied frames and flexible joints, allowing the structure to sway slightly without breaking. Properly reinforced columns, beams, and foundations help the building absorb the energy of seismic waves.

In addition, houses with simple shapes and fewer projections are generally safer during earthquakes.

Ans. When we walk on a carpeted floor or rub against synthetic clothes, our body may gain extra electrons and become negatively charged due to friction. The metal doorknob or car body is usually connected to the ground and is at a different potential. When we touch the metal, the excess charges on our body suddenly move to the metal and then to the Earth. This sudden flow of charge is a small electric discharge. We feel it as a mild shock or a tiny prick. This is a small-scale example of static electricity discharging, similar in principle to lightning but involving a much smaller amount of charge and energy.

Ans. A safety poster for thunderstorms and earthquakes should highlight simple, clear, and practical rules:

• For thunderstorms and lightning: Stay indoors; avoid using wired electrical appliances; keep away from windows and metal objects; do not stand under a tall tree or near electric poles; avoid open fields, rooftops, and water bodies; if outside, squat low on the ground.
• For earthquakes: Follow “Drop, Cover, and Hold” if inside; stay away from windows, tall furniture, and heavy hanging objects; do not use lifts; if outside, move to an open area away from buildings and electric poles; if near the sea, move to higher ground after a strong quake.

These key points help students remember what to do during emergencies and can be easily displayed on a safety poster in school.

Ans. Understanding natural phenomena like lightning and earthquakes helps us in many ways. First, it removes fear and superstition by explaining these events scientifically. Second, it teaches us correct safety measures, such as what to do during thunderstorms and earthquakes, which can save lives. Third, this knowledge helps engineers and planners design safer buildings, bridges, and electrical systems, reducing damage during natural disasters. Finally, awareness programmes based on scientific understanding encourage people to stay prepared and follow government guidelines. In this way, science not only helps us understand nature but also plays a key role in making our homes, schools, and society safer.