Natural Phenomena:

The phenomena that occur naturally are called natural phenomena.

Ex- Wind, Strom, Thunder, Cyclones, Earthquake, Lighting, etc.

Some natural phenomena are very destructive like Cyclones, Earthquake, Lighting, etc.

Basics of Atomic Structure: –

An atom is made up of electrons, protons and neutrons.

An electron carries a negative charge, a proton carries a positive charge and there is no charge on a neutron.

The number of electrons is equal to the number of protons. No(e) = No(p)

Electrically Neutral State of Matter:

Most of the matters are present in electrically neutral state in nature. Because in an electrically neutral atom, the number of electrons is equal to the number of protons. Thus, the equal numbers of negative and positive charges balance each other.

Charge: –  The physical properties of matter that causes it to experience a force when place in an electromagnetic field is called charge.

Type of charge: –   Positive charge (+)Ve and Negative charge (-)Ve.

Transfer of Charge: –  When certain objects are rubbed against another object, electrons may get transferred from one object to another.

      1.  If an object loses some electron, it has surplus number of protons. Thus, this object becomes positively charged.

      2.  If an object gains electron, it has surplus number of electrons. Thus, this object becomes negatively charged.

      3.  The transfer of charges is responsible for static electricity in various objects. Static electricity is the main reason of lightning.

Interaction of Charges:

When a glass rod is rubbed against a silk cloth; both of them get charged. As per convention; the glass rod is supposed to be positively charged and the silk cloth is supposed to be negatively charged once they are rubbed against each other. Some important observations about interaction of charges are as follows:

A charged object attracts an uncharged object:
Take a ball pen refill and rub it against a woollen cloth. Bring this refill near bits of paper. It is observed that the refill attracts the bits of paper. This activity shows that a charged object attracts uncharged object.
Take a comb and rub it vigorously in your hairs. Your hairs should be completely dry during this activity. Bring this comb near bits of paper. It is observed that the refill attracts the bits of paper. This activity shows that a charged object attracts uncharged object.
Like charges repel each other: (+)ve & (+)ve, (-)ve & (-)ve, Take two plastic balls and suspend them near each other. Rub a glass rod to induce charge in it. Touch both the balls with this glass rod. It is observed that the plastic balls move away from each other. This activity shows that like charges repel each other.
Unlike charges attract each other: (+)ve & (-)ve, (-)ve & (+)ve, Take two plastic balls and suspend them near each other. Rub a glass rod with a silk cloth. Touch one of the balls with the glass rod and touch another ball with the silk cloth. It is observed that both the balls move towards each other. This activity shows that unlike charges attract each other.

Electroscope

Electroscope is a simple device which is used to test the presence of charge in an object. The gold-leaf electroscope was developed in 1787 by a British scientist named Abraham Bennet. Gold and silver are among the best conductors of electric current and hence leaves of these metals are used in electroscope.

Structure of Electroscope: It is made of a glass jar. A vertical brass rod is inserted into the jar through a cork. The top of the brass rod has a horizontal brass rod or a brass disc. Two gold leaves are suspended from the brass rod; inside the jar. Working of Electroscope: When the brass disc of the electroscope is touched with a charged object, electric charge gets transferred to the gold leaf through the rod. This results in the gold leaves moving away from each other. This happens because both the leaves have similar charges.

 

Charging: –     Transfer of charge from one object to another is called charging. In case of the gold leaves; charge is transferred through the brass rods. Hence, it can be                                    said that charging can happen through metals.

Electrical Discharge: –    The losing of charge between two electrical charge objects is called electrical discharge.

      1.  The cause of discharging is contact, electrical short or dielectric breakdown.

      2.  Old leaves would also be discharged when someone touches the brass rod with bare hands. In that case, the charge is transferred to the earth through the human body.

Earthing: –     The process of transfer of charge to the earth is called earthing.

LIGHTNING: –   The transfer of charge from clouds to the earth or from cloud to cloud is called lightning.              OR

      1.  Lightning is an electric spark which happens on a grand scale in the sky.

      2.  Lightning is observed as a bright streak of light during a thunderstorm. Lightning is always accompanied by the sound of thunder.

Mechanism of Lightning

During a thunderstorm, the air currents move upward and water droplets move downward. These movements take at very fast pace and it results in separation of charges in the clouds. The positive charges accumulate at the upper edges of the clouds and the negative charges accumulate at the lower edges of the clouds. Scientists are yet to understand the exact reason for this. At the same time, the ground becomes positively charged.

Air is a bad conductor of electricity under normal circumstances (halat). But when the amount of charge becomes too much in the clouds, the air is not in a position to hold on to this charge. As a result, the electric charge is transferred to the ground. This appears like a bright streak of light across the sky; which lasts for a few seconds.

Dangers of Lightning: – Lightning can damage houses and trees. It can also kill people and cattle. Sometimes, lightning can main a person for life.

Safety During Lightning:

      1.  No open place is safe during lightning and hence a home or any other building is the safest place during lightning.

       2.  The first sound of thunder is like a warning call for lightning. Hence, one should rush to a building soon after hearing a sound of thunder. One should come out of                      home only a few minutes after the last sound of thunder.

       3.  You should not carry an umbrella (with a metallic handle) during thunderstorm. Metallic handle can be a potential target for lightning.

       4.  Tall trees and other tall structures are more prone to be hit by lightning. If you are caught in the open, try to hide under a short tree.

       5.   If you are in open and have no place to hide, then crouch on the ground and keep your head between your knees and hands.

        6.  Don’t take shower during lightning.

        7.   Use of phone should be avoided during lightning.

        8.  Television should be disconnected from the antenna.

        9.  Avoid operating the electric switches during lightning.

Lightning Conductor:

This is a simple device which protects a building from being hit by lightning. It is composed of a vertical metallic rod which usually has a trident (Trishul) at the top. The base of the metallic rod is attached to thick metallic wire; which goes very deep inside the earth. This metallic wire provides a passage for earthing.

When lightning strikes, electric charge goes to the lightning conductor and it then goes to earth. Thus, a lightning conductor helps in preventing any damage to the building.

Crust: –    The uppermost layer of the earth’s surface is called crust.

Earthquake: – Sudden shaking of the earth; which lasts for a very short duration is called earthquake.

Cause of earthquake–    When a tectonic plate brushes against another or strikes another tectonic plate; it results in vibrations in the tectonic plates. These vibrations are                        experienced by us in the form of an earthquake.

Tectonic Plates: – The crust of the earth is composed of several pieces of landmass. These are called tectonic plates.

The tectonic plates are in continuous motion. They keep on brushing against each other or striking each other.

Seismic or Fault Zones: –    The boundaries of the tectonic plates are called seismic zones or fault zones.

These boundaries are at high risk of earthquake. In India; Kashmir, western and central Himalayas, the whole of the north-east, Runn of Kutch, Rajasthan and Indo-Gangetic Plain are at high risk of getting hit by an earthquake.

Some parts of the Deccan Plateau are under the seismic zone.

Seismograph: –  The device which records the seismic activities is called seismograph.

It is composed of an oscillator, writing device and a roll of paper. The writing device is attached to the oscillator. In case of an earthquake, the oscillator begins to oscillate. This creates oscillation in the writing device; which plots wave-like patterns on the paper. The wave-like pattern is then analysed by seismologist to interpret the various features of an earthquake.

Richter Scale: –  The device which shows the intensity of earthquake is called Richter scale. 

    1.  It was developed in 1935 by Charles Richter and Beno Gutenberg of California Institute of Technology. This is a logarithmic scale which shows the intensity of an                     earthquake.

     2.  The intensity of an earthquake is measured on a scale of zero to 10.

     3.  But earthquakes of more than 9 Richter have never been reported.

     4.  An earthquake of magnitude 0 to 3 is not felt (Unnoticed).

     5.  An earthquake of magnitude up to 4.9 can be felt (Slight). and cause movement of loose objects.

     6.  An earthquake of magnitude 5.0 to 6.9 is moderate and cause furniture to move and trees to sway.

     7.  An earthquake of magnitude 7.0 to 7.9 is great and cause damage of weak structure.

     8.  An earthquake of magnitude 8.0 is very great and cause disastrous and destroy an entire city.

     9.  The magnitude of earthquake increases by 100 times when we move one point on the Richter scale. This means that an earthquake measuring 5 on Richter scale is 100               times more powerful than one measuring 4 on Richter scale.

Dangers Due to Earthquake

An earthquake cannot cause any damage on its own. Most of the damages caused by an earthquake are because of collapse of man-made structures; like buildings, bridges, poles, etc. Sometimes, an earthquake can result in tsunami which causes large scale damage. The infamous tsunami in the Indian Ocean which came on 26th December 2004 was because of a massive earthquake near Java.

Protection Against Earthquake:

It is impossible to predict an earthquake and hence we need to take several precautionary measures to avoid or minimize the damage which may happen because of earthquake. Some of the preventive measures are as follows:

     1.  Buildings should be made quake proof. Engineers and architects are the experts who can give suitable advice in this regard.

     2.  Light-weight materials should be used for making the buildings in earthquake prone areas.

     3.  Cupboards should be fixed to the walls so that they do not fall on someone during an earthquake.

     4.  People should be made to practice drills for earthquake. Such drills should be frequently organized in schools and at public places.

     5.  In case of an earthquake, you should hide under a table or any other similar structure. If you are in bed, then keep a pillow over your head and do not move out of the                bed. If you are in an open area, try to move away from buildings and other structures.

     6.  Proper installation of fire-fighting equipment’s should be ensured in buildings. Fire due to short circuit and gas leakage is quite common during an earthquake.