Some natural phenomena class 8 chapter 15 covers the following topics. The detailed view of class 8 science and some natural phenomena are provided in this article which enables students to understand class 8 some natural phenomena very easily.
Winds, storms, and cyclones are some natural phenomena. Those are phenomena of destruction. Two other destructive natural phenomena will be discussed here: lightning and earthquakes.
Electrically Neutral State of Matter:
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Most of the substances are neutral to electricity. An atom is composed of electrons, protons, and neutrons according to the basics of atomic structure. An electron carries a negative charge, a proton has a positive charge and a neutron has no charge.
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The number of electrons in an atom is equal to that of protons. The equal number of negative and positive charges are balancing among themselves. For this reason, most of the matter is electrically neutral.
Charging by Rubbing:
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Electrons may be transferred from one object to another upon rubbing two objects together. If an object loses any electron, it charges that object positively. If an object gains electrons, that object gets negatively charged. The static electricity is responsible for the transfer of charges in various objects. Static electricity is the principal reason for the illumination.
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Examples:
(i) When brushed with dry hair, a plastic comb acquires a small charge.
(ii) It acquires a slight electric charge when a plastic refill is rubbed with polythene.
(iii) The scale will draw very tiny pieces of paper as we rub a plastic scale on your dry hair.
Types of Charges and their Interaction
Activity (A):
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Two Inflated balloons hang them in such a way as not to touch one another. Rub both of the balloons and release them with a woolen cloth.
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We repeat that activity with the refills of the used pen. Refill one with polythene, then place it in a glass tumbler carefully. Refill the other with polythene too. Bring them close to the refill charged. We should not touch your hand to the charged edge.
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In both activities, the charged objects that were made of the same material and rubbed the same kind were brought closer together.
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Observation:
The balloons both repel each other. An additionally charged refill repels. -
Conclusion:
Same kind of charges repel each other.
Transfer of Charge and Earthing:
Electroscope:
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We take a bottle of empty jam and a piece of cardboard which is larger than the bottle ‘s mouth. Make a cardboard hole so that we can insert a paper clip made of metal. Clip of paper opened. Now we are cutting two-dimensional aluminum foil strips 4 cm /1 cm each. Hang them up as shown on the paper clip. We insert the paper clip perpendicular to the cardboard lid.
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By rubbing with polythene, we charge a refill, and touch it with the paper clip end. We observe they are repelling each other. Now that the paper clip ends, we touch other charged bodies. In all cases the foil strips act in the same way.
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Through the paper clip the aluminum foil strips receive the same kind of voltage from the charged refill (metals are good electric conductors) and repel each other and they become wide open.
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Such a tool could be used to check whether or not an object carries a charge. This device is called the Electroscope.
Earthing:
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Electric charge may be passed via a metal conductor from one filled device to another. When we gently touch the end of the paper clip with a hand, we will find that the electroscope foil strips return to their original condition.
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We repeat charging foil strips and touching the clip-on paper. We will find that the foil strips meet each other as we touch the paper clip with our hands. The reason is that the film strips lose charge through your body to the earth and the film strips become discharged.
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The process of transferring charge to earth from a charged object is called earthing.
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Earthing is provided in buildings to protect us against electrical shocks, due to any electrical current leakage.
Lightning:
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Lightning is a blinding flash of light with the sound of thunder during a thunderstorm. Lightning is also the movement of energy from cloud to cloud or from space to ground. In simple words, lightning is an electric bolt that happens in the atmosphere through rapid movement of air currents (upwards) and droplets of water (downwards) on a large scale.
The Story of Lightning:
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The air currents travel upward while creating a thunderstorm, and the droplets of water move downward. Because of these vigorous movements the burden in the clouds is separated.
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The positive charges from these produced charges accumulate near the upper edges of the clouds, and the negative charges accumulate near the lower edges of the clouds. Researchers have yet to understand the exact reason for this. Positive charges are also piled up near the ground.
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Once charges accumulate becomes very high, air, which under normal environment is a very poor conductor of electricity, is no longer able to resist their surge. As a result, the electrical charges transfer to the ground and generate streaks of bright light and sound throughout the sky. The process is known as electric discharge.
Dangers of Lightning:
Lightning Safety:
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No open place is safe during lightning and thunderstorms. A house is a safe place, or a building.
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First thunder sign is a warning to hurry to a more secure place. We should wait for some time after hearing the last thunder before we come out of the safe place.
Earthquakes:
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The earth’s rapid trembling or tremor, which lasts for a very short time, is considered an earthquake.
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It is caused by an upheaval deep inside the crust of the earth.
Causes of Earthquake:
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The tremors are caused by the movement deep down within the earth’s uppermost layer, called the crust.
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The crust of the earth is made of several parts of landmass. Those are also plate tectonics. Such plates are in continuous movement. Because of impact, as they run through each other, or a plate passes under another. They cause changes within the surface of the earth. These vibrations, which show us on earth’s surface as an earthquake.
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Earthquakes are more likely to occur at the edges of tectonic plates. Many borders or weak areas are referred to as earthquake or fault zones. In India; Kashmir, the western and central Himalayas, the entire northeast, Rann of Kutch, Rajasthan, and Indo-Gangetic Plain are at high risk of earthquake activity. Some areas of South India also fall under the seismic zone and within the danger zone.
Seismograph:
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Seismograph is a device that records the tremor-induced seismic waves. It is composed of an oscillator (a vibrating rod, or a pendulum), a typewriter and a paper roll. The oscillator is connected to the writing device.
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The oscillator will start vibrating in the event of an earthquake. This induces waves in the writing system and begins on paper to draw wave-like patterns. Scientists then study the wavelike pattern to build a complete map of the earthquake.
Richter Scale:
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The strength of an earthquake is expressed on a scale called the Richter scale, in terms of magnitude.
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Charles Richter and Beno Gutenberg, of the California Institute of Technology, created the Richter Scale in 1935.
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This shows how intense an earthquake is. The Earthquake intensity is measured on a logarithmic scale from zero to 10.
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Richter is not linear in size. A magnitude increase of 2 on the Richter scale signifies 1000 times more destructive energy. Example: a magnitude 6 earthquake has a thousand times greater destructive energy than a magnitude 4 earthquake.
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This indicates how powerful an earthquake is. An earthquake’s intensity is measured at a logarithmic scale of zero to 10.
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Richter is not regular in size. A magnitude rise of 2 on the Richter scale means 1000 times more disruptive force. Example: a magnitude 6 earthquake holds thousand times more destructive energy than a magnitude 4 earthquake.
Damages Due to Earthquake:
Protection Against Earthquake:
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Some of the preventive measures are as follows for the prevention or minimisation of earthquake damage:
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The buildings should be designed to endure tremors of great magnitude. Consult architects and structural engineers who are qualified to design quake proof buildings.
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The use of mud or wood is safer than the heavy building materials to make the structures vulnerable to earthquakes.
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Cupboards and shelves should be fixed to the walls so that during an earthquake they don’t easily fall on someone.
During the Earthquake, Take the Following Steps to Protect Yourself:
1. At Home:
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We should hide under a table during an earthquake. If you’re in hospital, put an ointment on your head and don’t get out of bed.
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We should stay away from high and heavy objects which might fall on you because of tremors.
2. At Outdoors:
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We should try to move away from buildings and trees, and from overhead power lines and other structures in an open area.
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Do not come out when you are in a car or a bus. Ask the driver to slowly drive into a clear spot. Do not come out until the shiver stops.
Natural phenomena can be defined as a naturally occurring process that occurs without any human input.Examples of natural phenomena include weather, gravity, fog, thunder, tides, erosion, biological processes and oscillation etc.
Static Charges
Methods of Charging
A body can be charged by rubbing two surfaces to each other due to friction.The electrical charges that are produced by the rubbing of two surfaces are called static charges.
Charging by Rubbing
Each and everyone of us has experienced this in our day to daylife that when objects like plastic get rubbed with hair, it attains a charge. In the same manner, a glass rod gets charged when rubbed with a silk cloth. The objects that are being rubbed get charged as they gain or lose electrons and hence they can attract or repel the small pieces of paper depending on the type of charge they are carrying at the time. So basically Like charges repel and unlike charges attract each other.
Electric Discharge
Electric Discharge is the process of flow of charge from one cloud to another or from cloud to earth due to the separation of positive and negative charges. During thunderstorms, air currents (that are warm in nature) move upwards and water droplets (cool in nature) move downwards. This causes a separation of charges among the clouds and between the clouds and the earth as well.
When the magnitude of charges increases, air, (a bad conductor) starts conducting. This facilitates the flow of electricity. This phenomenon is called lightning which is visible in the sky during a thunderstorm, as this flow of charge happens with bright streaks of light and sound.
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Lightning conductors help to protect buildings and large monuments during lightning.
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A Lightning conductor consists of a metallic rod that is taller than the building and is installed within the walls during construction. They act as a direct passage for electric discharge during lightning and safeguards the building from any calamity.
Earthquake
Earthquake is a natural phenomenon in which the surface of the earth starts trembling and shaking due to disturbances deep inside the earth’s crust. Earthquakes c
an be very dangerous and can cause large-scale damage to life and property.
Causes of Earthquake
Earthquakes are caused due to movement, shifting or collision of tectonic plates in the uppermost layer of the earth’s crust which leads to vibration on the surface.
Movement of Plates
Earth’s crust is divided into various fragments and each such fragment is known as a plate. These plates are constantly in motion and sometimes collide with each other, causing the earth surface to shake or tremble.
Seismograph
Seismograph is an instrument that is used to detect and record earthquakes. It takes the record of seismic waves caused by an earthquake. It consists of a mass that is attached to a fixed base, it starts vibrating when tremors occur.