CBSE Notes Class 8 Science Chapter 12 Some Natural Phenomena

Natural phenomena are events that take place in the environment without any human influence. They arise from various natural processes and can manifest in numerous ways, including changes in weather, geological activities, and astronomical events. By studying these phenomena, we deepen our understanding of Earth's processes, better equip ourselves to respond to natural disasters, and cultivate a greater appreciation for the beauty of our planet.

1.0Lightning

• Lightning is a natural electric discharge that occurs when charges accumulate in clouds.
• In ancient times, people feared lightning due to its unknown cause. Today, scientists have developed precautions to help us prepare for and protect ourselves from this phenomenon.
• The Greeks discovered electric charges around 600 BC, realizing that rubbing amber with fur allows amber to attract light objects like hair.

2.0Electric Charges and its Types

• Every atom consists of subatomic particles, including electrons, protons, and neutrons. Electrons carry a negative charge, whereas protons have a positive charge.
• An object is considered charged if there is an imbalance between the number of electrons and protons it contains. An object is said to be electrically neutral if it has an equal balance of positive and negative charges.

3.0Transfer of Charges

• Conduction occurs when a charged object comes into contact with a conductor, leading to the transfer of charges through the conductor.
• Induction due to when a charged object is brought close to a neutral object, causing the electrons in the neutral object to shift position. The process of induction does not require physical contact between the charged and uncharged objects, while conduction necessitates direct contact between them.

4.0Electroscope

• It is a device that can determine whether an object is charged.
• It consists of a glass jar with a vertical brass rod inserted through a cork. At the top, the rod has a brass disc or horizontal rod attached, while two gold leaves are suspended from the other end.
• When a charged object touches the brass disc, electric charges transfer from the brass rod to the gold leaves, causing them to repel and move apart, indicating the presence of charge.

5.0Earthing And Discharging

• When a charged object discharges its charges to the earth, this process is called earthing. Typically, buildings are equipped with earthing systems to protect against electrical shocks caused by current leakage.
• When a charged object loses its charge, it is referred to as being discharged.

6.0Lightning Conductor

• To protect buildings from lightning, a lightning conductor is installed during construction. This metallic rod, which extends above the building, has one end in the air and the other buried in the ground. As a conductor, it allows electric charges to flow safely to the ground during a lightning strike.
• The lightning conductor rod features pointed copper ends that extend down the building, connecting to a metallic plate in the ground. If lightning strikes, the copper wires swiftly channel the charges to the ground.

7.0Earthquakes

• Meteorologists can predict some natural phenomena, like thunderstorms and cyclones, but others, such as earthquakes, remain unpredictable. An earthquake is the shaking of the Earth's surface, typically lasting a short time. It is caused by disturbances within the Earth's crust. While minor quakes happen constantly deep underground, significant earthquakes that reach the surface can be highly destructive.
• Earthquakes can result in- Loss of life, destruction of property, including buildings, dams, and bridges.
• The Earth's surface consists of several layers: the crust, mantle, inner core, and outer core. The outer layer is divided into moving plates. When these plates shift or collide, they create disturbances in the crust, resulting in earthquakes or tremors.

Seismic Zones

• Plate movements trigger earthquakes, making their boundaries the most likely locations for seismic activity. Areas along these boundaries are referred to as weak zones, seismic zones, or fault zones.
• The Richter scale is used to calculate the magnitude or strength of an earthquake. Earthquakes with a magnitude greater than 7 on this scale are considered destructive.