CBSE NCERT Chapter 15 Class 8 Some Natural Phenomena Notes Pdf


Class 8 Some Natural Phenomena Notes

Let us revise the chapter with these beautiful and best Class 8 Some Natural Phenomena Notes from the Toppers Portal. We hope these Class 8 Some Natural Phenomena Notes help you fetch good marks in your CBSE or other examinations. We have tried to keep it short without missing the important points of the chapter.

Let us first look at the topics that we will study in this Class 8 chapter 15, Some Natural Phenomena.

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Chapter Overview:

  •  Define Natural Phenomena
  • Charges and their Types
  • Electroscope
  • Lightning
  • Thunderstorm
  • Earthquake
  • Safety Measures and Precautions

Natural Phenomena

Define Natural Phenomena.

Natural phenomena are events that occur in the nature or environment on their own or by the natural process. There is no direct involvement of human beings in the cause of Natural Phenomena.

These natural phenomena can be very destructive in nature, killing people, livestock, and their habitat.

Give some examples of Natural Phenomena.

Some examples of Natural Phenomena are- cyclones, Thunderstorms, hurricanes, tornados, Flood, Volcanic eruptions, etc.

Charges

What are electrical charges?

  • Electrical charges are the sub-atomic particles of an atom. Electrons, protons, and neutrons are sub-atomic particles.
  • The electron carries negative charges, the proton carries positive charges whereas the neutron is neutral i.e., has no charge.
  • Like or same charges repel each other (positive-positive or negative-negative)
  • Unlike or opposite charges attract each other (positive-negative)

Question: What is an uncharged body?

Ans: An object or a body that does not carry any charge or is electrically neutral.

Methods of Charging

There are basically three methods of charging an uncharged body. The three methods of charging an uncharged body are as follows-

  1. Method of Friction
  2. Method of Conduction
  3. Method of Induction

Method of Friction

The method of friction is a method of charging an uncharged body by rubbing it against other objects.

Example- When a glass rod is rubbed with a silk cloth, the glass rod acquires a positive charge by losing electrons. The glass rod is charged by the method of friction.

Method of Conduction

The method of Conduction is a method in which an uncharged object is charged by bringing or making contact with a charged body. The charges are transferred from the charged object to the uncharged object.

Method of Induction

In this method of Induction, the uncharged object is charged by bringing it near the charged object. The charged object induces a charge on the uncharged object.

Electroscope

An electroscope is a device that detects if a body is charged or not. We can also detect the type of charges on the test body if the gold leaves are charged.

Gold Leaf Electroscope was invented by Abraham Bennet.

What is the use of an Electroscope?

An electroscope is used to detect the presence of an electrical charge on an object or a body.

Construction of Electroscope

It consists of a glass container with a  long metallic rod inside it. One end of the wire is attached with two metallic strips and the other end is free with a metal disc attached, outside the glass container which is brought in contact with a charged object.

Working of Electroscope

When there is no charge on the free end of the metallic rod, the gold leaves are in the fully collapsed position. When a positively charged body is brought in contact with the free end, the negative charges flow towards the free end, leaving behind positive charges on the gold leaves and the gold leaves repel each other due to the same type of charges.

Similarly, when a negatively charged body is brought near or in contact with the metallic rod, the electrons are repelled and move down through the metallic rod and accumulate on the gold leaves. The gold leaves repel each other because of the same charges.

Lightning

It is an electrical spark on a larger scale and occurs due to the accumulation of many charges in the cloud.

It can also be defined as the discharging of electrical charges by the clouds. This discharging of charges by the clouds can be categorized in three ways-

  1. Discharging between the same clouds
  2. Discharging between two different clouds
  3. Discharging between clouds and the earth.

Define Discharging.

Discharging is the removal of excess charges by a charged body.

Define Earthing.

Earthing is defined as the discharging of charges to the earth. When the electric charges flow from an object to the earth is called Earthing.

Causes of Lightning

What causes lightning or how lightning occurs?

Clouds consist of positive and negative charges. Due to friction or rubbing charges separate themselves. The lighter positively charged particles move upward and the heavier negative charge particles (electrons) settle at the bottom. When these charged particles accumulate large enough, a spark is created due to the flow of the charged particles (same cloud, different clouds, and cloud to ground), thus causing lightning.

Do’s and Don’ts during Lighting

To avoid danger, we should adhere to some safety rules and take appropriate precautions when lightning strikes.

  • Don’t go in open spaces
  • Avoid umbrellas during lightning
  • Instead of hiding in long trees, hide under short trees
  • Instead of laying on the ground
  • Unplug electrical appliances
  • Stay away from windows, don’t take a bath

Earthquake

What is an Earthquake?

It is the sudden shaking of the earth that is caused due to disturbances inside the earth. An earthquake is a natural phenomenon that cannot be predicted accurately by meteorologists.

An earthquake can cause huge losses, buildings and other structures get damaged, dams may break and bridges or electricity poles get uprooted.

What is Seismology?

It is the study of earthquakes and their magnitude.

What is Seismograph?

The seismograph is an instrument that records seismic waves. It is a vibrating rod or a simple pendulum that vibrates when a tremor occurs. A pen is attached to the rod which records the waves on paper.

What is a Richter Scale?

It is a mathematical scale that is used to determine the magnitude of an earthquake.

  • It was developed by Charles Richter.
  • The magnitude is expressed in 0-10 numbers.
  • The points on the scale increase by a factor of 10.

Causes of Earthquake

An Earthquake is caused due to disturbances inside the earth. These disturbances are the result of the movement of tectonic plates that keep colliding along their boundaries. There are seven major tectonic plates (Pacific, North American, Eurasian, African, Antarctic, Indo-Australian, and South American) that comprise 95% of the earth. There are other minor plates also such as Arabian, Caribbean, etc.

The other causes of earthquakes are- volcanic eruptions, meteors

Do’s and Don’ts in Earthquake

We should take some precautions when an earthquake occurs or before the earthquake that minimize the damage.

  • Construct buildings after consulting architects and engineers.
  • Avoid going near tall buildings, or heavy objects during an earthquake
  • Hide under strong tables if inside room until earthquake stops
  • Move to open space during an earthquake
  • Stay away from electrical polls etc.

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