CBSE Class 8 Science Revision Notes Chapter 15

Class 8 Science Chapter 15 Notes

CBSE Class 8 Science Revision Notes Chapter 15 – Some Natural Phenomena

Natural phenomena are those that occur in nature without the intervention of humans. The causes, effects, properties, and magnitude of some of nature’s most destructive phenomena, such as lightning and earthquakes, are thoroughly discussed in Chapter 15 of CBSE Class 8 Science. The functions of an electroscope are discussed, as well as some steps to minimise the damage caused by these disastrous events.

Extramarks’ Class 8 Science Chapter 15 Some Natural Phenomena Notes will assist students in learning the chapter’s content in a short period of time with accurate and quality points. Subject matter experts prepare all of these notes and study material. Students can rely on these notes to revise Chapter 15 Some Natural Phenomena thoroughly. The Class 8 Science Chapter 15 Revision Notes is also easily accessible from the Extramarks website.

Revision Notes for CBSE Class 8 Science Chapter 15

Access Class 8 Science Chapter 15 – Some Natural Phenomena Notes

Protective Measures for an Earthquake:

When staying at home:

  • Hide behind a table and wait for the shaking to stop.
  • Keep a safe distance from tall, heavy objects that could fall on anyone.
  • Use a pillow to protect the head from any damage if in bed.

When outside:

  • Try to avoid areas with buildings, trees, and overhead electrical lines.
  • Lay on the ground.
  • If in a car or bus, do not get out of the vehicle. Instruct the driver to drive slowly to a safe location.
  • Only come out once the earthquakes have stopped.

Furthermore, it is critical to keep building structures simple for them to be ‘Quake Safe.’

Some Natural Phenomena Class 8 Science Revision Notes Chapter 15

Class 8 Science Chapter 15 is divided into seven sections. These subsections are discussed below:

  1. Lightning: Chapter 15 Science Class 8 begins with a discussion about lightning after a general introduction. It describes what lightning is and how it is perceived today versus ancient times. It also encourages students to create their own experience to learn how electric charge is related to lightning.
  2. Charging by Rubbing: The next section of Class 8 Science Chapter 15 discusses how an electric charge is created by rubbing two objects together. It includes an activity to encourage students to comprehend this natural phenomenon.
  3. Types of Charges and their Interaction: In this subtopic, students will learn how two similar charges are not attracted to each other. There are two activities that they can do at home to understand this concept better. For example, students can rub two inflated balloons with a woollen cloth in one experiment after which they repel each other after gaining charge.
  4. Charge Transfer: This section demonstrates how metal can transfer charge. In the activity described here, students can learn more about this concept by using a paperclip, an empty ball pen refill, and two strips of aluminium foil. They also learn about electroscopes, which are used to determine whether an object is charged or not.
  5. Story of Lightning: This section explains lighting in detail. Although still not fully understood, studies have shown that positive and negative charges in clouds cause this phenomenon. Before a thunderstorm, the air currents rise and the water droplets fall. It divides the currents. When the accumulation of these charges becomes too great, lightning or an electric discharge occurs.
  6. Lightning Safety: Students learn about the necessary safety precautions during thunderstorms and lightning in this section. It includes safe places to go to in such situations, as well as what to do and what not to do and goes over light conductors and their importance in building security.
  7. Earthquake: The final sub-topic in Class 8 Science Chapter 15 is an in-depth discussion of earthquakes. It is a complex and highly unpredictable natural occurrence. However, earthquakes can be predicted to some extent using modern equipment. The definition and causes of an earthquake, as well as how to stay safe during this natural occurrence, are covered.

Lightning and Earthquake

Lighting

Lightning is an electrical discharge or spark that occurs naturally. This is due to charge accumulation in the clouds. It can be fatal, resulting in the loss of life and property. People were afraid of lightning in ancient times because they didn’t know where it came from. Scientists have developed some measures to prepare for and defend against this natural occurrence.

Some Dos and Don’ts during a Thunderstorm or Lightning

During a thunderstorm, try to find a safe place, such as a house or a structure.

Avoid open spaces like fields and elevated places if outside.

Keep your distance from branches, poles, and metal objects.

Squat down and place your head between your knees on the ground.

Stop using any electrical appliances or running water if inside a house.

Earthquakes

An earthquake is a momentary shaking of the ground brought on by a movement far below the surface. The crust, mantle, outer core, and inner core are the four layers that make up the earth. The crust is not a unified structure that shields the inner layers. It is fragmented into smaller plates. These plates are constantly moving. When they collide or go above/below each other, they cause a disruption in the crust. An earthquake is caused by this collision.

The Richter scale is used to estimate an earthquake’s magnitude. The scale is based on the potential loss of lives and property that an earthquake can result in. The damage increases with the earthquake’s magnitude on this scale. Scientists have also developed a device known as a seismograph, which records the waves produced by tremors on the earth’s surface. This allows them to estimate their ability to cause harm.

Earthquakes can cause:

  • Fatalities
  • Destruction of property, such as buildings, dams, and bridges
  • Floods
  • Landslides
  • Tsunamis

Seismograph

Seismographs are instruments that record seismic waves. It consists of a metal rod or a pendulum that vibrates when an earthquake occurs. The metal rod is connected to a pen, which records the waves on paper. Scientists examine these waves and then map the earthquake. This also assists them in determining the magnitude of the earthquake.

Precautions for Earthquakes

  • Build earthquake-resistant homes.
  • To reduce damage, use wood and mud instead of cement and steel.
  • Cupboards and shelves can be attached to the wall.
  • Reduce the number of items hung in a building.
  • Always keep fire extinguishers on hand.

Here are some precautions to take during an earthquake:

  • Stay away from houses, trees, and power lines if outside. Maintain a low stance on the ground.
  • Sit down under a large table or bed if inside. Avoid objects that could collapse if the tremor intensifies.

Introduction to Charges

Every atom is made up of subatomic particles like electrons, protons, and neutrons. All of these particles have the property of carrying electrical charges in common. Protons are positively charged, while electrons are negatively charged. Although atoms have a balanced charge, these charges can frequently become out of order. If an object has a balanced proportion of positive and negative charges, it is considered electrically neutral.

Charging by Rubbing

When two objects are rubbed together, electrons transfer between them and charge the objects. When a rubber balloon is rubbed against animal fur, the rubber balloon attracts the electrons from the animal fur. As a result, rubber has an excess of electrons while fur has a deficiency of electrons. Similarly, rubbing a plastic comb against dry hair charges the comb.

Electroscope

It is a system capable of determining whether or not an object is charged. Gold and silver are frequently used to construct electroscopes because they are effective electrical conductors. Alternatively, copper and aluminium can be used. It is made up of a glass jar and a vertical brass bar. The rod is inserted into the pot through the cork. A disc or a horizontal rod is attached to the brass rod. Two gold leaves are suspended from the other end.

FAQs (Frequently Asked Questions)

The tremor caused by an earthquake causes vibrations on the earth’s surface in the form of waves known as seismic waves. Seismographs are instruments that record these waves.

Air currents move upward as water droplets move downward during the formation of a thunderstorm. These rapid movements allow charges to be separated. As a result, positive charges accumulate near the clouds’ upper edges, while negative charges accumulate near the clouds’ lower edges. There is also an accumulation of positive charge near the ground. As the volume of accumulated charges increases, the air, which is normally a poor conductor of electricity, will be unable to tolerate its flow.

Finally, when negative and positive charges come into contact, lightning and thunderstorms occur, which produce dazzling light flashes and tremendous sound. This is known as electrical discharge. This can happen both between clouds and the earth as well as between two or more clouds.

According to the most recent edition of India’s seismic zoning map, the earthquake design code divides the country into four seismic zones. According to the report, the most earthquake-prone states in India are Jammu and Kashmir, Gujarat, and Assam. These are the three states most vulnerable to earthquakes. Earthquake-prone areas in India include the Western and Central Himalayas, North and Middle Bihar, the North-East India region, and the Andaman and Nicobar Islands.

Two electrical charges with the same polarity combine to form an electric field and the forces that follow. The opposing charges seem to resist one another. A positive and a negative charge’s forces act in the same direction when they come into contact, drawing the two charges closer together. While opposite charges attract one another like charges repel one another.

Sweaters are made from wool, which is a poor conductor of electricity. When we put on the sweater, the wool comes into contact with our bodies, causing friction as our bodies rub against the wool. The wool becomes charged as a result of the rubbing, and a force is felt between the wool and our bodies. Because of this energy, we hear a cracking sound as we remove our sweaters in the winter.