SOME NATURAL PHENOMENA
Charged objects
The protons and neutrons are held very firmly in the nucleus of an atom. They cannot be
removed from an atom under ordinary conditions, but some of the electrons of an atom are
held loosely. They can move from one atom to another.
An atom that loses electrons has more positive charges (protons) than negative charges
(electrons). Such an atom is positively-charged. A charged atom is called an ion. A
positively-charged ion is called cation.
When an atom losses electrons, some other atom gains these electrons. An atom that gains
electrons has more negative charge. A negatively charges ion is called anion.
An object having positively charged atoms carries a positive charge whereas, an object
having negatively charged atoms carries a negative charge. A neutral object does not carry
ant charges. Due to imbalance in positive and negative charges, an atom acquired static
electricity.
How does an object acquire charge?
The simplest way of achieving this is by rubbing two objects made of different materials
such as plastic and wool. The electrons are transferred from one object to the other. The
more the rubbing, the more electrons move, and the larger is the static charge that builds
up in the two objects.
Lightning
Lightning is one of the most spectacular and powerful displays of energy produced by
nature. The intensity of the lightning and the frightening thunder that follows must have
often awakened you in the middle of the night. A lightning strike sometimes causes sever
damage to life and property. It can occur all of a sudden and at any time.
What causes lightning strikes?
1. During a thunderstorm, the movement in the clouds causes the charges in the water
molecules to separate in such a way that the positive charges concentrate at the
upper regions of the clouds and the negative charges concentrate on the base of the
clouds.
2. The negative charges at eh base of the clouds repel the negative charges from the
ground. This is because like charges repel. As a result, some of the negative charges
on the ground are pushed downwards away from the surface, leaving more positive
charges on the ball structures in the ground.
3. The negative charges at the base of the clouds pull the positive charges from the
ground upwards. The positive charges from the ground move upwards through tall
trees and buildings at a tremendous speed.
4. As soon as the negative and positive charges connect, a continuous path is formed
from the cloud to the structure on the ground.
5. The large amount of negative charges accumulated in the clouds rush down this path,
giving rise to a huge amount of static electricity. This is how lightning strike takes
place.
6. The sudden heating expands the air violently, and then contracts it. This creates a
sound which is known as thunder.
Effect of lightning
A lightning strike generates a huge amount of electric charge. The lightning bolt has a
temperature of about
28,000oC. It can damage buildings, burn trees, causes forest fires, kill animals and people
instantly.
A lightning conductor
1. A lightning conductor is a long rod made up of a metal such as copper which is a good
conductor of electricity
2. The rod is connected to a thick copper wire.
3. The wire is extended in to the ground and is attached to a metal disc.
4. The metal disc is buried in the ground. The soil where the dish is buried is kept moist.
5. A lightning conductor is usually installed on the tallest building in the area to prevent
the building from being struck by lightning during a thunderstorm.
Lightning also has some beneficial effects
(i) During lightning, the nitrogen and oxygen gases present in the air react to form nitrogen
oxide, which dissolves in the rainwater and mixes with the soil. These nitrogenous
substances present in the soil are used by the plants as nutrients.
(ii) During lightning, ozone (O3) is formed form oxygen (O2). The ozone layer in the
atmosphere protects the earth from the harmful ultra-violet radiations of the sun.
Earthquakes
1. An earthquake originates below the ground in the earth’s crust.
2. The spot from where the earthquake originates in the crust of the earth is called the
hypocenter or the focus of an earthquake. It is often several kilometres below the
earth’s surface.
3. The spot on the earth’s surface exactly above the hypocenter of an earthquake is the
epicenter.
4. The collision of plates gives rise to seismic waves.
5. Seismic waves are the vibrations from earthquakes that travel through the earth.
6. The damage caused by an earthquake depends on the intensity of these waves.
7. Power of an earthquake depends on the intensity of these waves.
8. Powerful seismic waves travel at a great speed and cover a large distance from the
epicenter of the earthquake.
9. A major earthquake is usually followed by minor earthquakes called aftershocks.
What is Richter scale?
1. The intensity of an earthquake is measured in Richter scale.
2. It has been developed by a scientist named Charles F Richter of the United States of
America.
3. The Richter scale reads from 1 to 10.
4. The intensity of an earthquake is recorded on a seismograph.
5. The seismograph records the slightest vibrations in the surface of the earth as zigzag
lines on a moving graph paper.
6. The time, location and magnitude of an earthquake can be determined from the data
recorded on a seismograph.
Where do earthquakes occur?
Earthquakes occur mostly at places where the tectonic plates meet.
They occur frequently around the Pacific Ocean where the volcanic ‘Ring of Fire’ is located.
The ring of fire is the name for the area where many of the world’s volcanoes are found.
Earthquakes are also common in the Mediterranean and the Himalaya-Asia region.
Safety measured to be taken during an earthquake
If outdoors
Move to an open area immediately.
Stay away from buildings, electric poles, trees, sign boards, bridges or any other structure
that can
crumble.
If you are travelling in a motor vehicle, bring it to a stop as quickly as possible.
Avoid being below bridges and overpasses.
If indoors
If possible, quickly move outdoors.
Move away from windows, swinging doors, large mirrors and hanging objects.
Take shelter under a desk, cot or table if it is sturdy.
Protect your head by wrapping your arms around it and curling into a ball.
Do not use a lift. It is safer to use the staircase.
Switch off gas and electric mains.
Do not use candles, matches or other naked flames as there may be gas leaks.
Listen to the radio for safety bulletins.
Store drinking water.
Do not use telephones, unless it is an emergency
Some Natural Phenomena Solved Questions
Q1. Why does a plastic comb rubbed with dry hair attract tiny pieces of paper?
Ans: Plastic comb gets electrically charged due to rubbing & therefore it attracts tiny pieces
of paper (which are neutral). As charged body can attracts an uncharged body.
Q2. Which of the following cannot be charged by friction, if held by hand?
a) a plastic scale b) a copper rod c) an inflated balloon d) a woolen cloth. and Why?
Ans: Copper rod.
Except copper, the other three are insulators whereas copper is a conducting object. As
soon as it gets charged by rubbing with another material, the electric charge produced on
its surface flow through our hand & body into the earth. And it remains uncharged.
Q3. What kind of electric charge is acquired?
a) by a glass rod rubbed with silk cloth? b) by a plastic comb rubbed with dry hair?
Ans: a) positive charge. b) Negative charge.
Q4. A negatively charged object attracts another charged object kept close to it. What is
the nature of charge on the other object?
Ans: Positive Or Neutral (uncharged).
Q5. A negatively charged object repels another charged object kept close to it. What is
the nature of charge on the other object?
Ans: Negative charge.
Q6. Mention three ways by which a body can be charged.
Ans: Three ways are:
a) Charging by rubbing: Charging of an object by rubbing it with another object is called
charging by rubbing.
NOTE: i) When two bodies are charged by rubbing, they acquire equal & opposite charges.
ii) The body which loses electrons acquires positive charge whereas the body which gains
electrons acquires negative charge.
b) Charging by conduction: Charging a neutral body by bringing it in contact with a charged
body is called charging by conduction.
c) Charging by induction: Charging a neutral body by bringing it near a charged body is
called charging by induction.
Q7. What is an electroscope? Explain its construction.
Ans: An electroscope is a device for detecting, measuring & finding the nature of
a charge.An electroscope consists of a large jar. A metal rod is fitted into the mouth of the
jar with the help of the cork. At the lower end of the metal rod a pair of thin leaves of gold
or aluminium is suspended.
Q8. What are the uses of an electroscope?
Ans: An electroscope can be used for following purposes:
a) To detect & measure the charge on a body.
b) To determine the nature of charge on a body.
Q9. How would you use an electroscope to find out whether an object is charged or not?
Ans: Touch the body to be tested with the metal disc of an electroscope. If the leaves of an
electroscope open up (diverge), the body is charged. If the leaves remain unaffected, the
body has no charge.
Note: The extent of divergence (opening apart) of the leaves is a measure of the charge on
the body. A body carrying higher charge will cause greater opening up of the leaves.
Q10. How would you use an electroscope to determine the nature of charge of a charged
body?
Ans: Charge the electroscope with a known charge, say with negative charge, by touching a
negatively charged ebonite rod to the metal disc of the electroscope. The leaves of the
electroscope open up (diverge).
Now touch the body to be tested with the metal disc of the charged electroscope.
If the divergence of the leaves increases, the body has similar charge that is the given body
is also negatively charged.
If the divergence of the leaves decreases, the body has unlike charge that is the given body
is positively charged.
Q11. What will you observe when the metal cap of an electroscope is touched with a
plastic comb rubbed in dry hair? Give reason for your answer.
Ans: After rubbing, plastic comb acquires negative charge. Now when it is touched with the
metal cap of an electroscope then both the metal cap & the leaves acquire negative charge
due to conduction. Because of negative charge on both the leaves, divergence of leaves
takes place.
Q12. What happens when we touch the metal cap of a charged electroscope with our
finger? What is this process known as?
Ans: The leaves of an electroscope collapse as soon as we touch the metal cap with hand
because the leaves of the charged electroscope lose charge to the earth through our body
(in other words leaves are discharged). This process is known as EARTHING.
NOTE: The process of transferring of charge from a charged object to the earth is called
Earthing.
Q13. What is the nature of charge a) on the metal cap b) on the leaves of an uncharged
electroscope when a negatively charged body is brought in contact with its metal cap?
Ans: a) Negative b) Negative
Q14. What is the nature of charge a) on the metal cap b) on the leaves of an uncharged
electroscope when a negatively charged body is brought near its metal cap (not in contact
withmetal cap).
Ans: a) Positive
b) Negative
Q15. Touch the disc of an electroscope first with glass rod rubbed with silk & then with
ebonite rod rubbed with fur. What do you observe & why?
Ans: After rubbing, glass rod acquires positive charge. Now when it is touched with the
metal cap of an electroscope then both the metal cap & the leaves acquire positive
charge due to conduction. Because of positive charge on both the leaves, divergence of
leaves takes place. Electroscope is now positively charged.
After rubbing with fur, ebonite rod acquire negative charge & when this negative rod
is touched with the metal cap of the above positively charged electroscope then
collapsing of leaves takes place as this negative charge starts neutralizing the positive
charge already present on the leaves.
Q16. Touch the disc of electroscope with an ebonite rod rubbed with fur. Now bring a
glass rod rubbed with silk close to the disc of this electroscope. What do you observe?
Ans: After rubbing, ebonite rod acquires negative charge. Now when it is touched with the
metal cap of an electroscope then both the metal cap & the leaves acquire negative charge
due to conduction. Because of negative charge on both the leaves, divergence of leaves
takes place. After rubbing with silk, glass rod acquire positive charge & when this positive
rod is brought near the metal cap of the above negatively charged electroscope then due
to induction positive charge gets induced in the leaves as a result collapsing of leaves
takes place.
18. What is seismograph?
Ans:Tremors or vibrations caused by the earthquakes which travel in the form of waves
within the earth or along the earth's surface, are called seismic waves. Seismograph is an
instrument which records these waves.
19. List two places in India which are most threatened by earthquake.
Ans: Two places in India which are most threatened by earthquake are 1. Kashmir 2. Rann
of kutch.
20. What are tectonic plates?
Ans: The earth's lithosphere is fragmented into many pieces. Each fragment is called a
plate, also called tectonic plate. These plates are in continuous motion i.e. they float over
hot magma.
21. What is a lightning conductor? Ans: Lightning
conductor is a device used to protect buildings from the
damaging effects of lightning. It runs from the top to the
bottom, along the outer wall of the buildings or any other
object, which is to be protected. If lightning strikes the
buildings or any other objects, then the lightning
conductor provides an easy and direct path for the
lighning bolt to pass to the ground without effecting them.
22. What is earthing? Ans: The process of transferring of charge from a charged object to
the earth is called earthing. For our safety, most of the electrical appliances and the mains
of the house are connected to earth, so that we can be prevented from getting an electric
shock.
23. We can easily charge non-metals like rubber, woollen clothes, plastics, etc. whereas
we cannot charge a copper rod by rubbing easily. Why?
Ans: When the metallic rods like copper rod are rubbed, charges does not build on their
surface because charges can escape through metals as they are conductors whereas when
non-metals like rubber, woollen clothes, plastics, etc. are rubbed, charges will build up on
their surface because charges are not conducted through them as they are insulators.
24. Explain the process of an electric discharge?
Ans: During the development of thunderstorm, air currents move in the upward direction
and the water droplets move in the downward direction. These movements causes the
seperation of charges. Usually, the negative charges accumulate at the lower part of the
clouds and the positive charges are accumulated at its upper part. The positive charges are
also accumulated at the ground also. When the accumulation of charges becomes large, a
high potential difference is set up between lower part of
clouds and earth, which is sufficient to break the
insulation of air. As a result, negative and positive charges
meet, producing streaks of bright light and sound. This
process is called an electric discharge.
25. Draw the diagram of an instrument, which can be
used to detect the charge on a body. How it can be
charged through conduction?
Ans: An electroscope is used to detect the charge on a
body.
A plastic comp is taken and it is rubbed on hair. Now, the plastic comb gets charged. The
comb is touched with the electroscope plate. The static charges which are developed on
the comb travels down the conducting wire and reach the two leaves of aluminium foil.
Similar charges are acquired by both the leaves and as a result, they repel each other. Thus,
the method of charging an uncharged body by bringing another charged body directly in
contact is called charging by conduction. Hence, by this way, an electroscope can be
charged through conduction.
26. Suppose you are outside your home and an earthquake strikes. What precaution
would you take to protect yourself?
Ans: The following precautions should be taken :1. Find a clear spot, away from buildings, trees, poles and electric poles, signboards and
overhead power lines anddrop to the ground.
2. Do not use elevators if they are available at some place outside your house.
3. If you are in a car or a bus, do not come out anddrive slowly to a clear spot. Stay inside a
cartill the tremors stop.
27. Suppose you are at your home and an earthquake strikes. What precaution would you
take to protect yourself?
Ans: The precautions that should be taken are :1. Take shelter under a table and stay there only, till the shaking stops.
2. Stay away from the objects which are tall and heavy, that may fall on you.
3. If you are on bed, do not get up and remain there only andprotect your head with pillow.
28. What is earthing? Why earthing is provided in buildings?
Ans: The process of transferring of charge from a charged object to the earth is called
earthing. Earthing is provided in buildings to protect them from electrical shocks due to any
leakage of electrical current. For our safety, most of the electrical appliances and the mains
of the house are connected to earth, so that we can be prevented from getting an electric
shock.
29. A crackling sound is heard while taking off sweater during winters. Explain ?
Ans:As we know that electrical charges that are generated through friction are static, i.e
they do not move by themselves and Motion of charges constitutes an electric current.
When we take off our sweater there is a motion between the charges on the sweater and
our body that produces electric current,which produces a crackling sound. Infact we can see
a spark if we take off the sweater in the dark.
30. What is lightning. Explain the experiment conducted by Benjamin Franklin that
showed sparks shared some similarity with lightning ?
Ans: Lightning is an atmospheric discharge of electricity, which typically occurs during
thunderstorms, and sometimes during volcanic eruptions or dust storms. In June 1752,
Benjamin Franklin raised a kite, accompanied by his son williams as an assistant. On his end
of the string he attached a key, and he tied it to a post with a silk thread .
After some time he noticed that small pieces of strings were beginning to stand apart like
the hair on the back of a scared dog. He then brought his hand close to the key and
received a tingle of an electric shock from the key.As the rain came down an the string
became soaked the electricity began to conduct freely throug the key.
31. What is an Earthquake?
Ans: An earthquake is a sudden shaking or trembling of the earth lasting for a very short
time.
32. What Causes an Earthquake?
Ans: Earthquake is caused by a disturbance deep inside the earth’s crust created by motion
of tectonic plate.
33. What could cause a disturbance inside the earth?
Ans: Some time moving tectonic plate goes under another due to collision and cause
a disturbance inside the earth.
34. What are seismic waves?
Ans: Waves produce by earth quake on the surface of earth is called seismic waves.
35. Where does the greatest number of earthquakes occur?
Ans: The boundaries of the tectonic plates are the weak zones where earthquakes are more
likely to occur. The weak zones are also known as seismic or fault zones.
36. What are different cases of tremors?
Ans: Tremors on the earth can be caused when a volcano erupts, or a meteor hits the earth,
or an underground nuclear explosion is carried out. However, most earthquakes are caused
by the movement of earth’s tectonic plates.
37. What is the scale used to measure magnitude of the intensity of earthquake?
Ans: Richter scale
38. What is the instrument used to measure seismic wave?
Ans: Seismograph.
The instrument is simply a vibrating rod, or a pendulum, which starts vibrating
when tremors occur. A pen is attached to the vibrating system. The pen records the
seismic waves on a paper which moves under it. By studying these waves, scientists
can construct a complete map of the earthquake
39.Define: hypocenter, epicenter, Seismic waves
Ans: The place below earth surface from where the earthquake originates is
called the hypocenter or the focus of an earthquake. It is often several kilometers below
the earth’s surface.
The spot on the earth’s surface exactly above the hypocenter of an earthquake
is the epicenter.
The collision of plates gives rise to vibration of earth surface called Seismic
waves this through the earth.
40. What safety measured you taken during an earthquake If you are traveling in a motor
vehicle?
Ans: Drive slowly and do not come out till the tremors stop.
41. What safety measured you taken during an earthquake If you are inside house?
Ans: Take shelter under a table and protect your head by wrapping your arms around it
and curling into a ball.
FILL IN THE BLANKS
1. Lightning is caused by______________.
2. The process of transferring charge from charged object to earth is
called___________.
3. The weak zones are also known____________.
4. The seismic waves are recorded in an instrument called___________.
5. ____________protect buildings from lightning.
6. Tremors are caused in the uppermost layer of the earth named as_________.
7. Power of earthquake expressed in terms of magnitude in scale called___________.
8. __________charges attract each other.
9. __________charges repel each other.
10.Each fragment in earth is called as_________.
11.Destructive earthquake have magnitude higher than_________.
12.Electric sparks at large scale is called as__________.
13.Lightning sparks could destroy___________&___________.
14. Point where earthquake originate is called as_________.
15.The electric charge generated by rubbing objects are called___________.
16.Device used to check weather device was charged or not is called as__________.
17.___________natural phenomena cannot be predicted.
18.The innermost layer of the earth is called___________.
19.Earthquake can cause_________&__________.
20.Lightning conductor is installed in the walls of___________.
21.Charges present near the ground are__________.
22.Charges present in the atmosphere are____________.
23. The charge acquired by a glass rod when it is rubbed with wool is__________.
24. Motion of charges constitutes an _________.
25. A charged balloon __________another charged balloon.
26. Lightning is an ____discharge.
27. Tremors are caused by ______waves .
28. Seismic waves are recorded by an instrument called the ________.
29. Earthquake is expressed in terms of a magnitude on a scale called a ___________.
30. The process of transferring of charge from a charged object to the earth is called
____________
31.The process of electric discharge can occur between two or more_______, or
between ________ and the __________.
32. The uppermost layer of the earth called the _________.
TRUE OR FALSE
1.
A cyclone can cause a lot of gain to human life and property. –F
2.
Snow is caused by the accumulation of change in the cloud. – F
3.
Weak zones are also known as fault zone. – T
4.
Some object can be charged by drawing with other object. –F
5.
There are two types of charge positive and negative charge. –T
6.
Like charges repel and unlike charger attract each other. – T
7.
The electrical charges produced by rubbing are called stat scope charge.-F
8.
When charge move, they constitute an electric current.-T
9.
An lance may be used to detect whether a body charged or not.-T
10.
The process of transfer of charged from an charged object to the earth is called
earthing.-T
11.
The process of electric discharge between cloud and the earth or between
different clouds causes lighting.-T
12.
Lighting strike could destroy life and property.-T
13.
Lighting conductor can gain buildings from the effect of lighting.-F
14.
An earthquake is a slow shaking of the earth.-T
15.
It is not possible to predicate the occurrence of the earthquake.-T