Science Chapter 15 Some Natural Phenomena

A.

A copper rod

B.

becomes positively charged while the cloth has a negative charge.

The crackling sound is heard due to electric discharge between sweater and body. 

Some energy is always released with electric discharge, in this case is released in form of a crackling sound. 

When we touch a charged body, it loses its charge, due to process of earthing.

Our body is good conductor of electricity and transfers the charges to the earth. 

Ritcher scale measures the rate of destructive energy of an earthquake.

A magnitude of 3 will be measured on the ritcher scale. It can be recorded on the seismograph. Earthquake measuring magnitude 3 will not cause much destruction as it is very less.  

Three measures to stay protected from lightning are:

(i) Stay indore or under covered area.

(ii) Don't take bath during lightning. Avoid any contact with running water. 

(iii) We should not use T.V. or phone during lightning. 

A charged balloon is repelled by another charged balloon because both carry the same charge.
We know that like charges always repel each other.

While the uncharged balloon is attracted by a charged balloon because unlike charges attract each other. 

An electroscope can be used to detect if a body is charged or not, and the relative amount of the charge.

 

The strips carrying similar charges repel each other and they become wide open as shown in the figure above. If the metal strips of the electroscope repel each other, the body is charged as repulsion is the sure test to detect if a body carries charge or not.

Both the bodies wil acquire the same charge and therefore, will repel each other. 

Positive charge.

Lightning is an electric spark on huge scale. Discharge of electricallt active ions happen on a large scale. 

Lightning is caused by the accumulation of charges in clouds. 

Huge energy is produced due to the repulsion of negative charges from clouds and positive charges from ground. When the magnitude of accumulated charges becomes very large, the air being a poor conductor of electricity is no longer able to resist the flow. Hence, streaks of bright light and sound is formed in the form of energy. 

The process of meeting of negative charges from clouds with positive charges from ground is called as Electric discharge. 

Metallic conductors are used to transfer electrical charges from one body to another. 

Earthing.

Earthing of wires is done in buildings to prevent electrocution. 

Earthing is provided in building to protect us from electrical shocks due to any leakage of electric current. 

In this circuit, parts of the electric circuit is connected with the ground, thus defining the electric potential of the conductors relative to the Earth's conductive surface. 

The process of transmission of negative and positive charges to release huge amount of energy is called electric discharge.

Flow of electrical charges (positive and negative), happen through mediums like solid, liquid and gas. 

Safe places during thunderstorm are:

1. Sit inside cars with windows shut.
2. If in an open area, squat low on the ground.
3. Stay inside the house. 

When in an open ground, we should take shelter under small trees, squat low on the ground so that you are the smallest target to be struck by ligtning. If travelling, then car or bus with windows and doors shut is a safe place. 

Lightning conductor.

The time of the next Earthquake cannot be predicted.

An earthquake is a sudden shaking or trembling of the earth which lasts for a few seconds or sometimes short duration of minutes.

Earthquake usually happens for a short duration of time. 

Tremors of earthquake are caused by the disturbance deep down inside the uppermost layer of the earth called the crust. 

The outermost layer of earth is fragmented and each fragment is called a plate. The plates are in continual motion. When these plates brush past one another, or undergo collision, they cause disturbance in Earth's crust. This disturbance shows up as earthquakes on the surface of the earth. 

Earthquake can cause floods, landslides and tsunamis.

The earthquake under the oceans causes Tsunami. 

Seismograph.

Earthquakes are caused by the movement of plates, the boundaries of the plates are weak zones where earthquakes are most likely to occur. The weak zones are also known as seismic or fault zones. 

The tremors produce waves on the surface of the earth. These waves are called seismic waves.

The point on the surface of the earth vertically above the focus is called epicentre.
The central point is called epicentre. 

The latest major earthquake in India occurred on 8th of October 2005 in Uri and Tangdhar town of north Kashmir. 

It is safe to use mobile phones and cordless phones.
Because, the wires of the landline would let the flow of electrons and hence, the chances of a person being electrocuted is more.

Air filled balloon when rubbed against hair gets charged. The charged balloon then sticks to the wall, when pressed against it. It is because the charged balloon and the wall will have unlike charges and will attract each other. 

When we touch one side of the paper strip with a charged rod, the paper strip opens up. The reason for this is that the two sides of the strip get the same type of charge from the charged rod and thus repel each other. With the result, the paper strip opens up (diverges). 

The figure below shows the divergence of metal strips when the positively charged rod is touched on one side of the strip. 

 

The point from where the shock-waves of an earthquake originate due to sudden movements is the seismic zone. The seismic zone or fault zone lies within the crust of the earth at a depth of about 60 km.

The point on the surface of the earth, vertically above the seismic focus is called epicentre. 

Lightning rods are installed on the top of the buildings as shown in the figure given below.



One end of the rod is left in open air and the other one is connected to the earth. When lightning strikes the building, the charges are directly transferred to earth by the rod, which is known as earthing.

Earthing thus saves the buildings from lightning strike.

Eel found in South America emits electric discharge from its body. It can produce electric current of 650 volts. It emits electric discharge to attack its enemies, to give shock to the prey.

As these Eels produce electric discharge, they are called electric Eels. 

Sudden trembling and shaking of the earth lasting for a very short time is an earthquake. 

 

Due to sudden movements in the uppermost layer of the earth, the earth starts trembling. This movement of earth is called an Earthquake.

The magnitude of the earthquake is measured through an instrument called seismograph and it is measured on Richter scale. 

A major earthquake hit Jammu and Kashmir and adjoining areas of Pakistan. Uri and Tangdhar towns of Kashmir were the most affected area. It occurred on 8th October 2005.
Prior to it a devastating earthquake hit Bhuj District in Gujarat on 26th January 2001. 

Disturbance deep under the crust of the earth causes earthquake. The uppermost layer of the earth is made with plates. These plates keep on moving. When these plates collide with each other, or when they slide up or down the other plate or move away, it causes earthquake. 

Electrical discharge is the transfer of charges from a body. On touching a charged object, the charge gets transferred to the earth through our body, our body being a good conductor of electricity. This way an object is discharged. The discharge of charge from body or any appliance to the earth is known as earthing.

Electrical discharge takes place between any two conducting bodies. 

The process of electrical discharge during lightning is explained as below: 

1. During thunderstorms, the air currents move upwards while the water droplets moves downwards. 2. These vigorous movement causes seperation between the charges. The positive charges gets accumulated near the upper edges of the clouds and the negative charges near the lower edges of the clouds. The positive charge gets accumulated on the surface of the ground also. 
3. When the magnitude of the accumulated charges becomes very large, the air which is normally a poor conductor of electricity, is no longer able to resist their flow.
4. When these negative and positive charges meet, electrical discharge takes place between clouds and grounds. 
5. It produces huge amount of energy which is released as streaks of bright light and sound. 

Mainly the earthquakes are caused by the collision or the movements of the plates on the crust of the earth. But sometimes it is also caused due to volcanic erruptions. It can also be caused by the hitting of meteors. Underground nuclear explosions also cause earthquakes. 

Regions which fall on the boundaries of the tectonic plates are called danger zones. The probability of earthquakes happening in these regions are more. These weak areas are also called fault zones or seismic zones.
 

India has many regions which fall under danger zone. 
The whole of the North East india fall under seismic zone. Kashmir, central and western himalayas are in danger zone. Western parts like rann of kutch, rajasthan are in fault areas. Besides these areas, indo-gangetic plane and some South Indian areas are also in seismic zone. 

Yes. Earthquakes bring about geographical changes on the surface of the earth. The earth starts experiencing tremors when earthquake strikes. There are times when large and deep slits appear on the earth. Earthquakes with high intensity cause strong movement of earth's surface that new islands and coral beaches get formed. Sometimes, fresh water springs are also formed due to the movement of the earth. 

To build an earthquake-safe house, the following measures can be used: 

(i) Qualified structural engineers and architects should be consulted while constructing the building.

(ii) It is necessary to make a symmetrical structure so that when an earthquake hits, the whole building sways uniformly, minimising the harmful effect of the earthquake to it.

(iii) Inside the building, extended structures like almirahs, cupboards, shelves etc., should be attached to the walls, so that they do not fall easily during a tremor. 

(iv) In high seismic areas, light construction materials should be used. Heavy construction material like cement, iron, concrete etc., should be avoided, rather mud, wood, etc., should be preferred. Roof should also be light, so that in case it falls, it causes less damage.

(v) Wall hangings, wall clocks, gysers, heaters etc., should be mounted on walls on those places, where they do not fall on people inside the building. 

(vi) Fire fighting instruments, first aid kits and other emergency equipments should be kept handy. 

Following safety measures should be taken in case of an earthquake strike:

(i) If, at home we should stick to the corners of the wall. 

(ii) Take shelter under a table and stay there till shaking stops. 

(iii) Stay away from windows, doors and heavy objects, so that they may not fall on you.

(iv) If we are out we should stay away from trees and buildings.

(v) We should stay inside vehicles, if we are travelling.

(vi) Vehicle should be driven away slowly to get cleared from the spot.

Lightning gives a warning before appearing. Huge thunder without light is a warning. We should look for a safe place. No place in open is safe.

(i) One should rush to take shelter in building or house.

(ii) One should not come out of the covered vehicle if on the road.

(iii) One should not take shelter under large and tall trees as they are easy target for electrical discharge.

(iv) One should not keep sitting on open vehicles like scooters, bikes etc.

(v) One should take shelter under smaller trees while in open as they are not easy target of lightning.

(vi) If in open and no tree or shelter nearabout, one should sit with head folded under arms and embedded between the legs. One should not lie down in open.

earthquake

lightning conductor

electroscope

lightning

epicentre

tsunamis

richter

metal conductor

thunder

A.

repel each other

C.

earthquake

A.

electric discharge

A.

lightning

B.

seismic focus

D.

only in the air

D.

8.0

B.

electroscope

A.

lightning conductor

B.

epicentre

The process in which negative and positive charges meet to produce streaks of bright light and sound is called electric discharge. 

The sketch below shows us the accumulation of charges on the surface of clouds and on the surface of ground. 

 

The given figure shows the lightning conductor. 

Ligtning conductor is used to protect buildings and houses from lightning. A metallic rod, taller than building is installed in the walls of the building during it's construction. The upper part of the ligtning conductor is left in the open and other end is buried deep into the ground. 

When lightning strikes, the rod provides easy route for the transfer of electric charge to the ground. 

Glass rod, being an insulator can be charged by holding it in our hand. This is because, the transfer of charge from the surface of the glass to our body does not take place. Hence, the glass remains charged.

Iron rod cannot be charged by rubbing when held in hand. Iron being a good conductor of electricity, transfer the charge produced on it into our body and is further transferred into the earth through our body. Therefore, the iron rod will continuously remain charge free. 

Carrying an umbrella during the thunderstorm is not a safe thing. During thunderstorms accompanied with lightning, electric discharge from the clouds can travel through the metallic rod of the umbrella, and may give an electric shock to the person who is carrying the umbrella.