# CBSE Class 8 Science Some Natural Phenomena Chapter Notes

## Study Material for Class 8 Science Chapter 15 Some Natural Phenomena

Class 8 Science students should refer to the following Pdf for Chapter 15 Some Natural Phenomena in Class 8. These notes and test paper with questions and answers for Class 8 Science will be very useful for exams and help you to score good marks

### Class 8 Science Chapter 15 Some Natural Phenomena

CBSE Class 8 Science Some Natural Phenomena Chapter Notes. There are many more useful educational material which the students can download in pdf format and use them for studies. Study material like concept maps, important and sure shot question banks, quick to learn flash cards, flow charts, mind maps, teacher notes, important formulas, past examinations question bank, important concepts taught by teachers. Students can download these useful educational material free and use them to get better marks in examinations.  Also refer to other worksheets for the same chapter and other subjects too. Use them for better understanding of the subjects.

Some Natural Phenomena

Electrostatics: Frictional Electricity
Electrostatics is the study of electric charges at rest. Therefore, it is also called ‘static electricity’. The charges at rest are produced due to friction between two insulating bodies which are rubbed against each other. That is why electrostatics is also called ‘frictional electricity’.
We know that when a glass rod is rubbed with a piece of silk, the rod acquires the property of attracting small pieces of paper, leaves, cork or even dust particles towards it. The rod is said to be electrified or charged. Similarly, a comb is electrified on passing through dry hair. When we take off a nylon shirt, we find little sparking. An electric charge also develops on a sheet of paper moving through a printing press and so on.

Electric Charge
Electric charge in an intrinsic characteristic of the fundamental particles making up our own bodies and the familiar objects that surround us i.e., electric charge is a characteristic that accompanies fundamental particles, wherever they exist.

The vast amount of charge in an object is usually hidden as the object contains equal amounts of positive charge and negative charge. With such an equal balance of charge, the object is said to be electrically neutral i.e. it contains no net charge.

If the positive and negative charges are not in balance, then there is a net charge. Thus an object is charged, if it has a charge imbalance or some net charge.

Atmospheric Electricity
The atmosphere of earth extends upto about 400 km above the earth’s surface. On the basis of distinct properties, the earth’s atmosphere is divided into four layers:
1. Troposphere 2. Stratosphere 3. Mesosphere 4. Ionosphere

Following are some of the important electrical properties of earth’s atmosphere.
1. Earth itself is good conductor of electricity.
2. The atmosphere near the surface of earth is a poor conductor of electricity. The conductivity increases, as we move up. Ionosphere is a very good conductor. This is primarily due to ionization of the molecules of air by charged cosmic ray particles having energies of the order of 1014 MeV.

Gold Leaf Electroscope (GLE)

It is an instrument used for the detection of electric charge and measurement of potential difference. The essential parts of GLE are shown in figure. D is a metallic disc, R is a metal rod; S is insulating stopper; L, L are gold leaves; G is a glass bell jar; F, F are in foils. M is insulating base on which a metal foil is pasted. When a charged body is held in contact with the disc D, the gold leaves diverge. The divergence of leaves is a measure of potential of the charged body.

Properties of Charge
1. A charged body is that body which has either excess of electrons or deficiency of electrons. A body having excess of electrons is negatively charged and a body having deficiency of electrons is positively charged.
2. Like point charges repel each other, while unlike point charges attract each other. The magnitude of force of attraction or repulsion is given by Coulomb’s law.
3. In charging, the mass of a body changes. If electrons are removed from the body, the mass of the body will decrease and the body will become positively charged.
4. Charge is quantised.
5. A large number of experiments show that in an isolated system, total charge does not change with time.
6. Charge is invariant, charge is independent of frame or reference, charge on a body does not change whatever be its speed.
8. If charged body is brought near a neutral body, the charged body will attract opposite charge and repel similar charge present in the neutral body. In case of induction it is worth noting that. Induced charge can be lesser or equal to inducing charge (but never greater) and its maximum value is given by;
q´= -q[ 1 -1/K]
K is the dielectric constant of the material, for metals, K =¥ and so q´ = –q i.e., in metals induced charge is equal and opposite to inducing charge.

DO you know ?
Can ever the whole charge of a body be transferred to the other? If yes, how and if not, why ?
Answer: Yes; if the charged body is enclosed by a conducting body and connected to it, the whole charge will be transferred to the conducting body, as charge resides on the outer surface of a conductor.

Coulomb’s law
If two point charges q1 and q2 are placed at a certain distance r, then the force of attraction or repulsion (F) between them depends as ,

r, being a pure ratio, has no units.

For example, r for water is 81

3. Coulomb’s law is applicable for point charges only.

4. The forces between two charges are mutual i.e., the forces on the two charges are equal in magnitude but opposite in directions.

5. The force is conservative, i.e, work done in moving a point charge once round a closed path under the action of Coulomb’s force is zero.

Some Natural Phenomena

Induction of Charge: When any charged object is brought close to an uncharged object, the total charge of the uncharged object gets polarised as follows:

In both case (a) and (b) without removing the charged object if the far side is touched (earthed) and then the charged object is removed then the uncharged object gain some net excess charge. This is the way we can charge an uncharged object by induction method. In this method the uncharged object gets opposite charge to that of the charged object.

Thunderstorms and Lightning Flashes

The mechanism of thunderstorm and lightning flashes is yet not well understood. However, the experimental observations lead us to the following facts:

1. All the world over, there occur about 4 × 104 thunderstorms per day.

2. In every thunderstorm, charged ions separate on account of some complex process which is yet not understood. The positive charges are carried to a height of about 6 km and negative charges collect at about 2 – 3 km. above the surface of earth. The lower level refers to the bottom of cloud and upper level refers to the top of the cloud.

3. The total amount of negative charge at the bottom of the cloud = 20 coulomb. Earth is at a higher potential. The potential difference between earth and cloud bottom is  107 to 198V. Therefore, an electric field of strength (E = V/d)  104V/m is created, directed upwards as shown in figure.

4. Such high electric fields cause an ‘electric breakdown’ of the air i.e. the intervening air gets ionized and conducts charge from the cloud to earth in the form of a lightning flash. Each flash lasts for 2 × 10–3 sec, and deposits about 20 C of charge on earth.

5. After each lightning flash, cloud becomes charged again and is ready for the next flash. With 90 flashes per second all over the world, about 1800 coulomb of negative charge is pumped into earth per second. This balance the +1800 coulomb inflow of charge per second into the earth from the thunderstorm – free regions. Thus the steady state of earth and its atmosphere are maintained.

Lightning Conductor

A lightning conductor is used to save big buildings from the damage by the lightning flashes. A lightning conductor consists of a number of pointed conductors fixed to the top of a building and connected to a thick copper wire. This wire runs down the side of the building and ends on a metal plate buried in the ground. When a negative charged cloud passes over the building, it induces a positive charge on the pointed ends of lightning conductor and an equal negative charge at the metal plate. Due to discharging action of sharp points, a positively charged electric wind is set up, which neutralises the negative charge on the cloud. The negative charge on the metal plate is immediately neutralized in the earth. If the discharge of the cloud occurs, it passes through the conducting copper strip and the building is saved from the damage.

Earthquakes

Any sudden disturbance below the earth’s surface may produce vibrations or tremors in the earth’s crust. These vibrations or shaking are known as earthquakes. In other words, the shaking of the ground caused by sudden movements of Earth’s crust is called in earthquake.
The enormous energy released by an earthquake travels through the ground in the form of waves. Thewaves generated by an earthquake are called seismic waves. These are recorded by an instrument, called seismograph or seismometer. The characteristics of an earthquake waves can be recorded on the screen of a seismograph, and is called a seismogram.
The science that deals with the seismic waves is called seismology and earthquake scientists are called seismologists.
The magnitude or intensity of an earthquake depends on the amount of energy released and is based on the direct measurement of the size of seismic waves.

Richter Scale

The magnitude or intensity of an earthquake is measured by the Richter scale, developed by measured by Charles F Richter, a US seismologist, in 1935. The number indicating the magnitude or intensity on Richter

scale ranges between 0 and 9. The Richter scale is not a linear scale. On this scale the vibrations of an earthquake with a magnitude of 2 are 10 times greater in amplitude than those of an earthquake with a magnitude of 1, and the vibrations of an earthquake with a magnitude of 8 are one million times greater in amplitude than those of an earthquake with a magnitude of 2. The severest earthquake ever recorded had magnitude of 8.7.

Earthquakes measuring 0-3 on the Richter scale are often not even noticed. An earthquake of intensity 4.5 is considered moderate and can disturb loose objects. At intensity 5.5, the earthquake is strong and can cause furniture to move and trees to sway. At intensity 6.5 an earthquake can damage weak structures. An earthquake of intensity 8 or more can be very disastrous and can destroy entire cities.

Main causes of Earthquake

The Earth’s lithosphere is divided into about 20 parts called tectonic plates.These plates float over the hot magma below, and are therefore in relative motion to each other. When these plates collide and the rock at the joint is sufficiently slippery, the plates slide over each other, little by little. However, sometimes the rocks at the joints can interlock and get stuck, resisting pressure from within. For years, the forces pushing the plates build up until the strain can rip the two plates apart. The rocks crack and shift, sending shock waves of energy in all directions. When these waves reach the surface, they are felt as earthquakes. The point from which the earthquake waves originate is called the seismic focus. It lies within the crust of the earth. The point on the earth’s surface vertically above the focus is called the epicentre of the earthquake.,The intensity of the earthquake is greatest at the epicentre.
The boundaries of the tectonic plates are the zones where earthquakes are most likely to occur. These are known as seismic or fault zones. In India faulty zone at the boundary of the Indian plate and Eurasian plate passes through Kashmir, western and central Himalayas, the whole of North-East, Rann of Kachchh, Rajasthan and the Indo-Gangetic plain. These areas are therefore most prone to earthquakes.

Protection against Earthquake

It is very difficulty to predict the occurrence of an earthquake, as it occurs suddenly. Violent earthquakes are often desructive. They cause serious damage to life and property. We can take the following precautions against earthquakes while building our houses. The following are some steps you should take if you are caught in an earthquake.

• If trapped in your home or a building take shelter under a table and do not move till the shaking stops. Protect your head with your arms. Avoid using lift.

Do not stay near the windows, bookcase, mirrors, hanging pots, fans during or immediately after an earthquake.

Leave your home or school building and move to open areas.

If outdoors, keep away from high-rise buildings, trees, signboards, poles and electric poles and electric wires.

Do not sit inside a car or a bus.

Help others according to their needs.

EXERCISES

1. Name the charged particles present inside an atom.

2. An insulator loses some electrons. What type of charge will be developed in the insulator and what will be its potential.

3. How can be charge induced in an uncharged object.

4. Write any three properties of charge.

5. A person coming out of a car touches the door get electric shock. How do you explain this fact.

6. What is a lightning conductor? How does it work.

7. Is there any charge in the atmosphere? If yes then where it is?

8. What are uses of a gold leaf electroscope?

9. A(+) 5 coulomb and (–) 10 coulomb charge are seperated by a distance of 1 m. How much force in Newton will act between them ?

10. What type of protection can be taken to avoid any damage caused by lightning.

11. A positively charged rod is brought closer to the head of an electroscope. What type of charge will be developed at its leaves.

12. Write different possible reasons for which clouds get charged.

1. A body has 80 microcoulomb of charge. Number of additional electrons in it will be
(A) 8 × 10–5 (B) 80 × 10–17
(C) 5 × 10-14 (D) 1.28 × 10–37

2. Two charge placed in air repel each other by a force of 10–4 N. When oil is introduced between the charges, the force becomes 2.5 × 10–5. The dielectric constant of oil is
(A) 2.5 (B) 0.25
(C) 2.0 (D) 4.0

3. Two charges of 2 microcoulomb are 0.5 m apart. If both of them exist inside vacuum, then force between them is
(A) 1.89 N (B) 2.44 N
(C) 0.144 N (D) 3.144 N

4. Two electrons are separated by a distance of 1Å. What is the coulomb force between them
(A) 2.3 × 10–8C (B) 4.6 ×  10–8C
(C) 1.5 ×  10–8C (D) None of these

5. The point at which the earthquake originates is known as
(A) Mentles (B) Seismic focus
(C) Surface wave (D) Body wave

6. Lightning is a process of
(A) Producing positive charges (B) Detecting negative charges
(C) Electric discharge (D) None of the above

 Class 8 Science Crop Production and Management Exam Notes
 Class 8 Science Microorganisms Exam Notes
 Class 8 Science Materials Exam Notes Class 8 Science Metals and Non Metals Exam Notes
 Class 8 Science Coal and Petroleum Exam Notes
 Class 8 Science Combustion and Flame Exam Notes
 Class 8 Science Conservation of Plants and Animals Exam Notes
 Class 8 Science Cell Exam Notes
 Class 8 Science Reproduction Exam Notes
 Class 8 Science Reaching at the Age of Adolescence Exam Notes
 CBSE Class 8 Science Force and Pressure Chapter Notes Class 8 Science Force and Pressure Exam Notes
 CBSE Class 8 Science Current Electricity and its Effects Chapter Notes Class 8 Science Chemical Effects of Electric Current Exam Notes
 CBSE Class 8 Science Some Natural Phenomena Chapter Notes Class 8 Science Some Natural Phenomena Exam Notes
 Class 8 Science Pollution of Air and Water Exam Notes
 CBSE Class 8 Science Heat Chapter Notes

## More Study Material

### CBSE Class 8 Science Chapter 15 Some Natural Phenomena Study Material

We hope students liked the above Study Material for Chapter 15 Some Natural Phenomena designed as per the latest syllabus for Class 8 Science released by CBSE. Students of Class 8 should download the Study Material in Pdf format, read the notes and related questions and solutions given in above Class 8 Science Study Material on daily basis. All latest Study Material have been developed for Science by referring to the most important and regularly asked topics which the students should learn and practice to get better score in school tests and examinations. Studiestoday is the best portal for Class 8 students to get all latest study material free of cost.

### Study Material for Science CBSE Class 8 Chapter 15 Some Natural Phenomena

Expert teachers of studiestoday have referred to NCERT book for Class 8 Science to develop the Science Class 8 Study Material. If you download Study Material for the above chapter daily, you will get higher and better marks in Class 8 test and exams in the current year as you will be able to have stronger understanding of all concepts. Daily reading of Science study material will help students to have stronger understanding of all concepts and also make them expert on all critical topics. You can easily download and save all Study Material for Class 8 Science also from www.studiestoday.com without paying anything in Pdf format. After solving the questions given in the Study Material which have been developed as per latest course books also refer to the NCERT solutions for Class 8 Science designed by our teachers

#### Chapter 15 Some Natural Phenomena Study Material Science CBSE Class 8

All Study Material given above for Class 8 Science have been made as per the latest syllabus and books issued for the current academic year. The students of Class 8 can refer to the answers which have been also provided by our teachers for all Study Material of Science so that you are able to solve the questions and then compare your answers with the solutions provided by us. We have also provided lot of MCQ questions for Class 8 Science so that you can solve questions relating to all topics given in each chapter. Also download Class 8 Science Sample Papers given on studiestoday.

#### Chapter 15 Some Natural Phenomena CBSE Class 8 Study Material Science

Regular Study Material reading helps to gain more comprehensive understanding of Chapter 15 Some Natural Phenomena concepts. Study Material play an important role in developing understanding of Chapter 15 Some Natural Phenomena in CBSE Class 8. Students can download and save or print all the Study Material, printable assignments, practice sheets of the above chapter in Class 8 Science in Pdf format from studiestoday. You can print or read them online on your computer or mobile or any other device. After solving these you should also refer to Class 8 Science MCQ Test for the same chapter

#### CBSE Study Material Science Class 8 Chapter 15 Some Natural Phenomena

CBSE Class 8 Science best textbooks have been used for writing the problems given in the above Study Material. If you have tests coming up then you should revise all concepts relating to Chapter 15 Some Natural Phenomena and then take out print of the above Study Material and attempt all problems. We have also provided a lot of other Study Material for Class 8 Science which you can use to further make yourself better in Science.

How to download CBSE Class 8 Science Chapter 15 Some Natural Phenomena study material

You can download free study material for Class 8 Science Chapter 15 Some Natural Phenomena for latest academic session from StudiesToday.com

Can I download study material for Chapter 15 Some Natural Phenomena Class 8 Science in Pdf format

Yes, you can click on the link above and download PDFs for Class 8 Science Chapter 15 Some Natural Phenomena easily for regular use

Is the study material for Chapter 15 Some Natural Phenomena Class 8 Science for the latest CBSE academic session

Yes, the study material given here for Class 8 Science Chapter 15 Some Natural Phenomena is for current CBSE session

Can I download Chapter 15 Some Natural Phenomena Class 8 Science study notes in pdf

You, just click the link above and save Class 8 study material for Science Chapter 15 Some Natural Phenomena in Pdf

Is there any charge for Class 8 Science Chapter 15 Some Natural Phenomena concepts and study material

All study maetrial for CBSE Class 8 Science Chapter 15 Some Natural Phenomena is free

Tell me the best website to get study material for Chapter 15 Some Natural Phenomena Class 8 Science

www.studiestoday.com is the best portal for Chapter 15 Some Natural Phenomena Science Class 8 study material

How to get topic-wise study material for Class 8 Science Chapter 15 Some Natural Phenomena

Visit www.studiestoday.com for best study material for Class 8 Science Chapter 15 Some Natural Phenomena

How to print Chapter 15 Some Natural Phenomena Class 8 Science study notes as per CBSE syllabus

All study material for various topics of Class 8 Science Chapter 15 Some Natural Phenomena as per latest CBSE syllabus is avaiable here