Extra 20 important long questions and answers for the "Some Natural Phenomena" chapter:12 of Class 8 CBSE Science:-
Q: Explain the phenomenon of lightning and how it is formed.
A:
Lightning is a massive electrical discharge that occurs in the atmosphere.
It is caused by the accumulation of static electric charges within clouds due to friction between water droplets, ice crystals, and air.
Positive charges accumulate at the top of the cloud, and negative charges at the bottom.
When the charge difference becomes large enough, a rapid discharge of electricity occurs.
This discharge heats the air, causing it to expand rapidly and produce thunder.
Lightning can occur between clouds, within a cloud, or between a cloud and the ground.
Q: Describe the safety measures to be taken during a thunderstorm.
A:
Seek shelter inside a building or a car.
Avoid open fields, tall trees, and water bodies.
Stay away from windows and doors.
Do not use electrical appliances or telephones.
If outdoors, crouch low to the ground, but do not lie flat.
If in water, get out immediately and move to a safe shelter.
Q: Explain the causes and effects of earthquakes.
A:
Earthquakes are caused by the sudden movement of tectonic plates in the Earth’s crust.
These plates move along fault lines, and when they get stuck, pressure builds up.
When the pressure is released, it causes a sudden jolt, resulting in an earthquake.
The effects include ground shaking, which can cause buildings to collapse.
Earthquakes can also trigger landslides, tsunamis, and fires.
The magnitude of an earthquake is measured by the
Richter
scale, that is a logarithmic scale.
Q: Describe the safety measures to be taken during an earthquake.
A:
If indoors, take cover under a sturdy table or desk.
Stay away from windows, mirrors, and hanging objects.
If outdoors, move to an open area away from buildings and trees.
Do not use elevators.
If in a vehicle, stop and stay inside until the shaking stops.
After the earthquake, check for injuries and damage, and follow emergency instructions.
Q: Explain the formation of cyclones and their impact on coastal areas.
A:
Cyclones are formed over warm ocean waters due to low-pressure areas.
Warm, moist air rises, creating a low-pressure
center
called the “eye.”
Air rushes in to fill the low-pressure area, causing strong winds and heavy rainfall.
The rotation of the Earth causes the storm to spin.
Coastal areas are highly vulnerable to cyclones, which can cause storm surges, flooding, and damage to property.
Early warning systems, and cyclone shelters are very important to minimize damage, and loss of life.
Q: Describe the role of a lightning conductor in protecting buildings from lightning.
A:
A lightning conductor is a metallic rod installed on the top of a building.
It provides a low-resistance path for lightning to travel to the ground.
The rod is connected to a thick copper wire that runs down the side of the building.
The wire is connected to a metal plate buried deep in the ground.
When lightning strikes, the conductor safely diverts the electrical discharge to the ground.
This prevents damage to the building and protects people inside.
Q: Explain the concept of static electricity and how charges are transferred.
A:
Static electricity is the
build-up
of electric charges on the surface of objects.
It occurs when certain materials are rubbed together, causing electrons to transfer from one material to another.
Materials that lose electrons become positively charged, and those that gain electrons become negatively charged.
Like charges repel each other, and unlike charges attract each other.
The discharge of static electricity can cause sparks or shocks.
An electroscope can be used to detect static electricity.
Q: Describe the structure and function of an electroscope.
A:
An electroscope is a device used to detect the presence and nature of electric charges.
It consists of a metal rod with two thin metal leaves (usually gold or
aluminium
) attached to its lower end.
The rod is insulated from the container.
When a charged object is brought near the top of the rod, the leaves diverge due to electrostatic repulsion.
The degree of divergence indicates the amount of charge.
The nature of the charge can be determined by bringing a known charged object near the electroscope.
Q: Explain the formation of thunderstorms and their associated phenomena.
A:
Thunderstorms are formed by the rapid upward movement of warm, moist air.
This leads to the formation of cumulonimbus clouds, which contain water droplets, ice crystals, and hailstones.
Friction between these particles causes static electric charges to build up.
The discharge of these charges causes lightning and thunder.
Thunderstorms can also produce strong winds, heavy rainfall, and hailstorms.
They are associated with unstable atmospheric conditions.
Q: Describe the role of seismic zones in earthquake occurrence and prediction.
A:
Seismic zones are areas where earthquakes are more likely to occur due to the presence of fault lines.
These zones are often located along the boundaries of tectonic plates.
Scientists study seismic zones to understand earthquake patterns and predict future events.
Seismographs are used to monitor ground movements and detect tremors.
Earthquake prediction is still challenging, but seismic zoning helps in planning safe construction and disaster preparedness.
Building codes in seismic zones are very strict.
Q: Explain the relationship between warm ocean temperatures and cyclone intensity.
A:
Warm ocean temperatures provide the energy needed for cyclones to form and intensify.
The warmer the ocean, the more moisture evaporates, creating a low-pressure area.
This low-pressure area draws in more warm, moist air,
fuelling
the cyclone.
As the cyclone moves over cooler waters or land, it loses energy and weakens.
Climate change and global warming is causing ocean temperatures to rise, which may increase the frequency and intensity of cyclones.
This creates a greater threat to coastal populations.
Q: Describe the process of charging by induction and its applications.
A:
Charging by induction occurs when a charged object is brought near a neutral conductor without touching it.
The charged object induces a separation of charges in the neutral conductor.
If the conductor is grounded, the induced charges can be removed, leaving the conductor with an opposite charge.
Applications include electrostatic painting, where charged paint particles are attracted to a grounded object.
It is also used in photocopiers, and laser printers.
Induction is used in many industrial applications.
Q: Explain the formation and effects of tsunamis caused by earthquakes.
A:
Tsunamis are large ocean waves caused by underwater earthquakes, volcanic eruptions, or landslides.
The sudden vertical movement of the seafloor displaces a large volume of water, creating waves.
These waves can travel across oceans at high speeds.
When they reach shallow coastal areas, they increase in height, causing devastating flooding.
Tsunamis can cause widespread destruction, loss of life, and damage to infrastructure.
Early warning systems are crucial for saving lives.
Q: Describe the role of atmospheric pressure in the formation of cyclones.
A:
Cyclones are characterized by a low-pressure
center
, known as the "eye."
The low pressure draws in surrounding air, creating strong winds.
As warm, moist air rises, it cools and condenses, releasing heat and further lowering the pressure.
The pressure gradient between the eye and the surrounding air drives the cyclone's circulation.
The stronger the pressure gradient, the more intense the cyclone.
Atmospheric pressure is a key factor in cyclone formation, and intensity.
Q: Explain how seismographs are used to detect and measure earthquakes.
A:
Seismographs are instruments that detect and record ground motions caused by earthquakes.
They consist of a mass suspended by a spring or pendulum, and a recording device.
When an earthquake occurs, the ground moves, and the seismograph records the vibrations.
The recordings, called seismograms, provide information about the earthquake's magnitude, location, and depth.
Seismographs are essential for monitoring seismic activity and studying earthquake patterns.
Networks of seismographs are used to create earthquake maps.
Q: Describe the process of how a lightning rod dissipates a lightning strike.
A:
Lightning rods are made of a conductive material such as copper.
They are placed at the highest point of a structure.
The rod provides a path for the lightning to travel.
The electrical charge travels through the rod, and the connected wire.
The charge is dissipated into the ground through the ground plate.
This protects the building from damage from the lightning.
Q: Explain the process of how clouds become electrically charged.
A:
Within storm clouds, there are ice crystals, water droplets, and hail.
These particles collide as they are moved by air currents.
Smaller, positively charged ice crystals are carried upward.
Heavier, negatively charged hail and water droplets fall.
This separation of charges creates a powerful electric field.
Eventually the electrical potential is great enough to cause lightning.
Q: Describe how to prepare a building to withstand an earthquake.
A:
Buildings should be constructed with reinforced concrete and steel.
Foundations should be designed to resist ground movement.
Walls should be anchored to the foundation and roof.
Flexible connections should be used for pipes and wiring.
Buildings should be regularly inspected for damage.
Emergency plans should be in place, and practiced.
Q: Explain the safety precautions taken when a cyclone warning is issued.
A:
Listen to radio or television broadcasts for updates.
Move to a safe shelter or higher ground.
Secure loose objects around your home.
Store enough food and water.
Stay indoors until the storm has passed.
Follow the instructions of local authorities.
Q: Describe the difference between the focus and
epicenter
of an earthquake.
A:
The focus is the point inside the earth where the earthquake originates.
The
epicenter
is the point on the earth’s surface directly above the focus.
Seismic waves radiate outwards from the focus.
The
epicenter
is where the strongest shaking occurs.
The
epicenter
is used to determine the location of the earthquake.
The focus is used to determine the depth of the earthquake.
