Some Natural Phenomena Class 8 Free Study Material pdf

5 SOME NATURAL
PHENOMENA
5.1
5.2
5.3
Electrical charges
Methods of charging
Some natural
phenomena
5.1 ELECTRICAL CHARGES
5.1.1 Electrical charges in atoms
 The smallest particle into which
an element can be divided and
still have the properties of that
element
 consists of protons, neutrons and
electrons.
The beside figure shows electrons moving in
different orbits around the nucleus.
 Each electron has 1 unit of negative
charge.
 Each proton has 1 unit of positive
charge.
 Neutron is a particle without an electrical
charge within the atomic nucleus.
Under normal conditions, an atom contains equal number of positive and
negative charges. As the charges cancel out each other, an atom is
electrically neutral.
The positively charged protons are bound firmly to the atom while the
negatively charged electrons are loosely bound. When an atom loses an
electron, it becomes positively charged while in the similar manner, on
gaining an electron, it becomes negatively charged. Rubbing is one such
method to remove some electrons from an atom.
Example of a carbon atom is shown
beside which contains 6 neutrons, 6
protons and 6 electrons.
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5.1.2 Static electricity
Presence of electric charge causes the formation of static electricity. It can be acquired by rubbing two
bodies. They are called static because they can’t move. However, when charges move, it comes under
electric current.
There exist only two kinds of charge in the universe i.e. positive charge and negative charge.
STATIC ELECTRICITY DEMONSTRATION
Step 1 - Blow up a rubber balloon and tie the neck
Step 2 - Rub the balloon against a piece of wool, fur or sweater.
Step 3 - Place the balloon against the wall: the balloon should stick to the wall.
Step 4 - Now blow up another balloon and repeat step 2. Place it next to the balloon.
The friction from the rubbing transfers free electrons from the wool and makes the
balloon negatively charged. When held against the positively charged wall, the
unlike charges attract, the two objects will stick together.
5.1.3 The gold leaf electroscope
Gold leaf electroscope is an instrument for detecting and measuring static electricity or voltage.
A metal disc is connected to a narrow metal plate and a thin piece of gold leaf is fixed to the plate. The
whole of this part of the electroscope is insulated from the body of the instrument. A glass front prevents
air draughts but allows one to watch the behavior of the leaf.
A gold leaf electroscope
When a charge is put on the disc at the top it spreads down to the plate and leaf. This means that both the
leaf and plate will have the same charge. Similar charges repel each other and so the leaf rises away from
the plate - the bigger the charge the more the leaf rises.
The leaf can be made to fall again by touching the disc - you have earthed the electroscope. An earth
terminal prevents the case from becoming live. The electroscope can be charged in two ways:

 By contact - A charged rod is touched on the surface of the disc and some of the charge is transferred
to the electroscope. This is not a very effective method of charging the electroscope.
 By induction - A charged rod is brought up to the disc and then the electroscope is earthed, the rod is
then removed.
The two methods give the gold leaf opposite charges. The diagrams below show how the charges spread
over the plate and gold leaf in different conditions.
Charging by contact
Charging by induction
5.2 METHODS OF CHARGING
Three methods of charging are by - friction, conduction and induction.
5.2.1 By friction/rubbing
Rubbing two different materials together, a process known as charging by friction (charging by rubbing),
is the simplest way to give something a charge. This is what you do every time you drag your feet along a
carpet so you can reach out and zap someone's ear. Your feet in socks and the carpet are doing charging
by friction. Since the two objects are made of different materials, their atoms will hold onto their
electrons with different strengths. As they pass over each other the electrons with weaker bonds are
“ripped” off one material and collect on the other material.
Example - Rub a piece of ebonite (very hard, black rubber) across a piece of animal fur. Explain what
happens.

The fur does not hold on to its electrons as strongly as the ebonite. At least some of the electrons will be
ripped off of the fur and stay on the ebonite. Now the fur has a slightly positive charge (it lost some
electrons) and the ebonite is slightly negative charged (it gained some electrons). The net charge is still
zero between the two. Remember the conservation of charge - no charges can be created or destroyed,
they just moved around.
5.2.2 By conduction
Conduction just means that the two objects will come into actual physical contact with each other (this is
why it is sometimes called “charging by contact”).
Let's assume we have a negatively charged metal object and an uncharged metal object (illustration a).
They are similar objects, and each is on an insulating stand so that we can move them around without
them interacting with anything else.
We bring the two objects close together. We will see a separation of charge happen in the neutral object
as negative electrons are repelled to the right hand side (illustration b). At this time, they are not touching
and no charges have been transferred.
Next, we allow the two objects to touch (illustration c). Some of the negative charge will transfer over to
the uncharged metal object. This happens since the negative charges on the first object are repelling each
other; by moving onto the second object they spread away from each other.
When the negative object is removed, it will not be as negative as it was (illustration d). Both of the
objects have some of the negative charge. This depends on the size of the objects and the materials they
are made of. Since they are similar in this example they have the same magnitude charge.
5.2.3 By induction
It is possible to charge a conductor without touching or rubbing it by bringing a charged body near it.
This is called charging by induction. Here, the body being charged acquires an opposite charge to that of
the body charging it.

Most important is the use of a grounding wire. A grounding wire is simply a conductor that connects the
object to the ground. Think of the earth as a huge reservoir of charge. It can both gain and donate
electrons as needed. Depending on what the situation is, either electron will travel up the grounding wire
to the object being charged, or travel down to the ground.
Charging by induction is a more complex process than conduction, as the example below shows.
Illustration a: The neutral object is on an insulating stand. It also has a ground wire attached to it.
Illustration b: We bring a negative object nearby. This will cause the electrons to be pushed as far away
as possible, and since they are free to move, they do just that. They will travel down the ground wire.
Illustration c: This step is VERY important. Keeping the negative object nearby we snip the ground wire.
Now there is no way for the electrons to travel back up they wire to the originally neutral object. If we
had skipped this step and just moved the negative object away without snipping the ground wire, the
negative charges would have just gone back up the wire and it would be neutral again.
Illustration d: We remove the negative object. Now the original object has a net positive charge.
 Exercise 1:
What do you mean by earthing?
5.3 SOME NATURAL PHENOMENA
5.3.1 Lightning and thunder
What is lightning?
Lightning can be seen virtually instantaneously. It takes 3 seconds to travel a kilometre. Lightning can be
seen up to 50 miles away. The distance of a lightning flash can be estimated by counting the seconds
between seeing the lightning and hearing the thunderstorm. Lightning is produced by discharges of

electricity from cloud to cloud or from cloud to ground. A large positive charge builds up in the upper
part of a thunder cloud and a negative charge builds up near the base of the cloud. When the potential
difference between the charged areas becomes large enough, electrical energy is discharged and a flash of
lightning occurs. Huge quantities of electricity are discharged in lightning flashes and temperatures of
over 30,000°C or more can be reached.
Lightning is commonly of two types – sheet lightning and forked lightning. In case of sheet lightning, the
charge leaps from one side of a cloud to the other. Whereas in forked lightning, the charge leaps to the
earth, sometimes branching out to other clouds on the way down.
Thunder is the sound created by the expansion of air created by lightning. Lightning is an electric
discharge in the atmosphere. It represents a quick moving flow of charge between the clouds and the
ground. Along with lightning, large amount of heat is produced which generates pressure waves and that
is transmitted in all possible direction causing sound which is termed as thunder.
Lightning helps fertilize plants. Our atmosphere consists of approximately 70% nitrogen, but this nitrogen
exists in a form that plant life cannot use. Lightning strikes help dissolve this unusable nitrogen in water,
which then creates a natural fertilizer that plants can absorb through their roots. Lightning also produces
ozone, a vital gas in our atmosphere that helps shield the planet from rays of harmful ultraviolet sunlight.
Safety measures during lightning strikes
 When you see lightning, even when it’s not raining, you should go inside a sturdy building. Lightning
can strike up to 15 miles away from a thunder-storm.
 When inside your house, stay off any electronics plugged into the wall, the phone, and stay away
from doors and windows. If you need to communicate, use text messaging on your cell phone, which
will leave telephone lines available for emergency personnel.
 If you’re unable to get inside a building, you should go to a car or vehicle with a top. The sides and
top of the vehicle will help protect you. Uncovered convertibles, mopeds, and motorcycles are not
safe from lightning. The most important rule to remember when staying safe from lightning is:
WHEN THUNDER ROARS, GO INDOORS!
 Never stand near or beneath a tree and also standing on the open ground is also not recommended.
LIGHTNING CONDUCTORS
Damages due to lightning flashes are very common. But with the help
of a lightning conductor we can save our large buildings on which we
have spent lots of money. The lightning conductor consists of large no.
of conductors having sharp pointing heads. They are usually attached
on the top of buildings. Their pointing heads are connected to a
conducting material such as a copper wire. This copper wire of large
length comes down along the either side of the building. At the bottom
it is attached to a metallic plate that is interred into the ground. Clouds
mostly contain positive charge. Whenever the passage of cloud occurs over a certain building then
induced charges are produced. At the pointing heads of the conductor, induced positive charges are
produced and on the metal plate induced negative charges are produced. The pointing heads of the
conductor have the property of discharging the positive charges present on it and ultimately, a positively
charged wind is produced. On account of this wind, the negative charges of the cloud are counteracted i.e.
cancelled out. The charge of the cloud after discharging flows to the ground with the help of the copper

wire. Hence our building will be saved by using lightning conductors.
5.3.2 Earthquake
What is an earthquake?
An earthquake is what happens when two blocks of the earth suddenly slip past one another. The surface
where they slip is called the fault or fault plane. The location below the earth’s surface where the
earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is
called the epicenter.
Sometimes an earthquake has foreshocks. These are
smaller earthquakes that happen in the same place as the
larger earthquake that follows. Scientists can’t tell that
an earthquake is a foreshock until the larger earthquake
happens. The largest, main earthquake is called the
mainshock. Mainshocks always have aftershocks that
follow. These are smaller earthquakes that occur
afterwards in the same place as the mainshock.
Depending on the size of the mainshock, aftershocks can
continue for weeks, months, and even years after the
mainshock.
What causes earthquakes and where do they happen?
The earth has four major layers: the inner
core, outer core, mantle and crust. The
crust and the top of the mantle make up a
thin skin on the surface of our planet. But
this skin is not all in one piece – it is
made up of many pieces like a puzzle
covering the surface of the earth. Not
only that, but these puzzle pieces keep
slowly moving around, sliding past one
another and bumping into each other. We
call these puzzle pieces tectonic plates,
and the edges of the plates are called the
plate boundaries. The plate boundaries
are made up of many faults, and most of
the earthquakes around the world occur
on these faults. Since the edges of the plates are rough, they get stuck while the rest of the plate keeps
moving. Finally, when the plate has moved far enough, the edges unstick on one of the faults and there is
an earthquake.
Why does the earth shake when there is an earthquake?
While the edges of faults are stuck together, and the rest of the block is moving, the energy that would
normally cause the blocks to slide past one another is being stored up. When the force of the moving
blocks finally overcomes the friction of the jagged edges of the fault and it unsticks, all that stored up
energy is released. The energy radiates outward from the fault in all directions in the form of seismic

waves like ripples on a pond. The seismic waves shake the earth as they move through it, and when the
waves reach the earth’s surface, they shake the ground and anything on it, like our houses and us.
How are earthquakes recorded?
Earthquakes are recorded by instruments called seismographs/
seismometers. The recording they make is called a seismogram.
The seismograph has a base that sets firmly in the ground, and a
heavy weight that hangs free. When an earthquake causes the
ground to shake, the base of the seismograph shakes too, but the
hanging weight does not. Instead the spring or string that it is
hanging from absorbs all the movement. The difference in
position between the shaking part of the seismograph and the
motionless part is what is recorded.
The power of an earthquake is expressed in terms of a magnitude
on a scale called the Richter scale.
Safety measures
Before an earthquake
 Be prepared to act. Know how to act so your response is automatic. Identify safe places in your work
area to ‘Drop, Cover and Hold On.’ Know at least two ways to exit the building safely after an
earthquake.
 Stock up emergency supplies. Keep the basics: flashlight, first-aid kit, whistle, gloves, goggles,
blankets and sturdy shoes. Coordinate supplies with your work group or department. Plan as if food
and water may not be available for about 24 hours and other supplies for up to 3 days.
 Arrange your work area for safety. Make sure that bookcases, large file cabinets and artworks are
anchored. Store heavy objects on lower shelves. Store breakable objects in cabinets with latches. Use
normal work order process to get furniture anchored.
During an earthquake
 Remain calm as the quake occurs – others will respond to your actions. A cool head can prevent
panic. If you are indoors when the shaking occurs, stay there. Move away from windows and
unsecured tall furniture. Drop, cover and hold on under a desk, a table or along an interior wall.
Protect your head, neck and face. Stay under cover until the shaking stops and debris settles.
 If you are outdoors, move to an open area away from falling hazards such as trees, power lines, and
buildings. Drop to the ground and cover your head and neck.
After an earthquake
 Remain calm and reassuring. Check yourself and others for injuries. Do not move injured people
unless they are in danger. Use your training to provide first aid, use fire extinguishers and clean up
spills. In laboratories, safely shut down processes when possible.
 Expect aftershocks. After large earthquakes, tremors and aftershocks can continue for days.
 Be ready to act without electricity or lights. Know how to move around your work area and how to
exit in the dark. Know how to access and use your emergency supplies. Be aware of objects that have
shifted during the quake.
 If you must leave a building, use extreme caution. Continually assess your surroundings and be on the
lookout for falling debris and other hazards. Take your keys, personal items and emergency supplies

with you if safe to do so. Do not re-enter damaged buildings until an all-clear is given.
 Use telephones only to report a life-threatening emergency. Cell and hard-line phone systems will be
jammed. Text messages take less band width and may go through when voice calls can’t be made.
Recovery from earthquakes
The effect of earthquake is long term and people of that area need to be evacuated and rehabilitated.
Following steps are necessary for recovery from earthquakes.
 Check the injured person and provide them with first aids.
 Check the hazards like fire, gas leaks and damaged electrical wirings.
 Telephone lines should be left free for emergency use.
 Expect aftershocks as these are smaller than the main but may be large enough to cause additional
ones.
 Help according to the need.
 Exercise 2:
Mention some of the worst Indian earthquakes.
ANSWERS TO EXERCISE
Exercise 1: The process of transferring of charge from a charged object to the earth is called earthing.
Exercise 2: Kashmir, 2005 – 8.1 magnitude on Richter scale
Bhuj, Gujarat, 2001 – 8.1 magnitude on Richter scale
Uttarkashi, 1991 – 6.4 magnitude on Richter scale
Anjar, Gujarat, 1956 – 8.5 magnitude on Richter scale

Solved Examples
Example 1
How can you test whether a body is charged or not?
Solution
For test of charging, you are advised to bring a positive and negative charged body one by one near to
the body of interest. If it is repelled by the positive charged body then it is also positively charged. If it is
repelled by the negatively charged body, then it is also negatively charged. Thus repulsion is the
certainty test for finding a charged body.
Example 2
Where do the two types of charges come from?
Solution
Electric charges are actually present inside atoms. Every atom contains particles with positive and
negative electric charges. The positively charged particles are firmly bound to the atoms while the
negatively charged particles are more loosely bound. It is possible to remove some of the negatively
charged particles by process such as rubbing.
Example 3
What is the cause of thunder?
Solution
When a lightning bolt travels through the air, electron flows take place which leaves behind a little
hollow channel in the air. After the electron flow is over, the surmounting air rushes back to reoccupy
the hole due to existing vacuum. The hollow channel collapses as air rushes in, making the deafening
clap of sound that we call thunder.
Example 4
Why do people in coastal areas shift to nearby raised grounds after an earthquake?
Solution
Earthquake in coastal areas results in tsunamis which are very high tides and can be large enough the
size of a city. It can extend upto several metres/kilometres high and can submerge nearby areas
completely. Thus, people shift to nearby raised grounds.
Example 5
Which among the following cannot be charged easily by friction?
plastic scale, copper rod, inflated balloon, woollen cloth
Solution
Copper rod
Example 6
Sometimes, a crackling sound is heard while taking off sweater during winters. Explain
Solution
Normally, sweaters are made of wool and the other inner clothes like shirts are made of cotton and
synthetic fibres. Due to friction among these, static charge gets accumulated on the sweater. While
taking off sweater, an electric discharge occurs between sweater and the body which results in forming
of sparks and crackling sound.

Example 7
How can a body be charged by induction?
Solution
A body can be charged by bringing a charged body near to it, but not touching it. This phenomenon is
called induction. Here, the body being charged acquires an opposite charge to that of body charging it.
Example 8
Inflate a balloon and rub it against your dry hair and then gently place it against a wall. What do you
observe? Explain.
Solution
We observe that the balloon sticks to the wall. The balloon acquires an electric charge when it is rubbed
against the hair and here, the balloon and the wall acquire opposite charges and attract each other.
Example 9
What do you mean by earthing?
Solution
The process of transfer of charges from a charged object to earth is known as earthing. Earthing is used
to discharge an electroscope before it can be used for another experiment.
Example 10
Describe the methods of charging by friction.
Solution
When two bodies are rubbed against each other, they acquire equal and opposite charges. When you rub
a glass rod with silk, the glass rod acquires a positive charge. The silk cloth acquires a negative charge.
When two bodies are rubbed together, there is a friction between them. So, a body can be charged by
friction.
Example 11
Petrol tankers along the highways often have metal chains attached to it and that drag along the road.
Why is it so?
Solution
It is because the motion of petrol produces charges when the tanker moves. So the charge will flow to
the ground through the chain. If the metal chain is not attached then due to the production of charges the
tanker may get in fire.
Example 12
What is seismic focus? Where is it situated?
Solution
The point at which the earthquake wall originates is called the seismic focus. It lies within the crust of
the earth. The point on the earth surface vertically above the focus is called epicenter of the earthquake.
Example 13
Explain why a charged body loses its charge if we touch it with our hand.
Solution
Human body is a good conductor of electricity. A charged body loses its charge when we touch it with
hand because the charges get transferred through our body to earth (earthing).

Example 14
How rubbing generates charge?
Solution
On rubbing two objects against each other, they acquire equal and opposite charges. This is because
some of the negatively charged particles on a body are transferred to the other body. This results in
electron losing body to acquire positive charge and electron gaining body to acquire negative charge.
Example 15
Name the scale on which the destructive energy of an earthquake is measured. An earthquake
measures 3 on this scale. Would it be recorded by a seismograph? Is it likely to cause much damage?
Solution
Richter scale measures the destructive energy of an earthquake. Yes, seismograph can measure an
earthquake of magnitude 3 on Richter scale. It is of low intensity and will not cause any damage.
Example 16
Write down the precautions we should follow against earthquakes?
Solution
In high seismic areas, use of timber is better than bricks and concrete. Roofs should be as light as
possible. Building constructions should follow quake proof norms. Firefighting equipment should be
installed and kept in working order.
Example 17
Suggest three measures to protect ourselves from lightning.
Solution
 Open space is dangerous. Take cover under a building.
 Thunder storm is an indication to rush for safer place.
 Once thundering stops, move out to an open place.
Example 18
List three states in India where earthquakes are more likely to strike.
Solution
Three states in India are Gujarat, Rajasthan and Himachal Pradesh.
In India, the areas most threatened are Kashmir, Western and Central Himalayas, the whole of North-
East, Rann of Kutch, Rajasthan and the Indo – Gangetic Plane. Some areas of South India also fall in the
danger zone.
Example 19
Lightning strikes more frequently in hilly areas. Why?
Solution
In hilly areas clouds are comparatively closer to the ground than in plains. Hence, lightning strikes are
more frequent in hilly areas.
Example 20
Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon
is attracted by another charged balloon?
Solution
Two charged balloons have similar charges on the surfaces. Since like charges repel each other, that's

why one charged balloon is repelled by another charged balloon. When an uncharged balloon is brought
near a charged one, the uncharged balloon acquires some opposite charge. Since unlike charges attract
each other, therefore a charged balloon attracts an uncharged one.
Example 21
Suppose you are outside your home and an earthquake strikes. What precaution would you take to
protect yourself?
Solution
During the earthquake, I would take the following precaution -
 I would try to find a clear spot, away from buildings, trees and overhead power lines and drop to the
ground.
 If I am in a car or a bus, I would ask the driver to drive slowly to a clearer spot and would not come
out till the tremors stop.
Example 22
The weather department has predicted that a thunderstorm is likely to occur on a certain day.
Suppose you have to go out on that day. Would you carry an umbrella? Explain.
Solution
Carrying umbrella is not a good idea at all during thunderstorms. As during the thunderstorm, the speed
of wind will blow away the umbrella.
******

EXERCISE
 Multiple choice questions with one correct answer
1. Two charged objects are brought close to each other. Choose the most appropriate statement from the
following options:
(A) they may attract
(B) they may repel
(C) they may attract or repel depending on the type of charges they carry
(D) there will be no effect
2. The earth’s plate responsible for causing earthquakes is
(A) crust (B) mantle (C) inner core (D) outer core
3. Vibration accompanying an earthquake is
(A) seismic waves (B) tremor (C) fault (D) moment
4. Earthing is provided in buildings to
(A) avoid electric shocks due to any leakage of electric current
(B) protect it from the danger of earthquakes
(C) both (A) and (B)
(D) none of these
5. When we remove polyester or woolen cloth in the dark, we can see spark and hear a crackling sound.
These are due to
(A) reflection of light (B) refraction of light (C) current electricity (D) static electricity
6. Where is the safest place to be during a lightning storm?
(A) In a car (B) In a house (C) Middle of the field (D) Both (A) and (B)
7. Which of the following is not likely to cause Tsunami?
(A) under sea nuclear
explosion
(B) Earthquake (C) Volcanic eruption (D) Lightning
8. Which of the following lies on the earth’s surface?
(A) Seismic focus (B) Epicentre (C) Mantle (D) Core
9. Before using electroscope, it should be
(A) charged (B) discharged (C) cleaned (D) closed
10. The molten rock which comes out during volcanic eruption is called
(A) mixture (B) magma (C) mud (D) ash
11. Electric current is to be passed from one body to another. For this purpose the two bodies must be joined
by
(A) cotton thread (B) plastic string (C) copper wire (D) rubber band

12. Which theory explains the location of earthquakes, volcanic eruptions and newly forming mountains?
(A) Theory of plate
tectonic
(B) Theory of evolution (C) None of these (D) Both (A) and (B)
13. Richter scale is developed by
(A) William Richard (B) Benjamin Franklin (C) Benjamin Richter (D) Charles F Richter
14. Circular mass of clouds indicate the formation of
(A) cyclones (B) flood (C) earthquake (D) tsunami
15. The charge silk acquires when rubbed with a glass rod is
(A) positive (B) negative (C) neutral (D) both (A) and (B)
16. Which of the following scales are not linear in nature? (i) Decibel (ii) Richter (iii) Meter
(A) (i) only (B) (ii) and (iii) only (C) (ii) only (D) (i) and (ii) only
17. An electroscope is a device which is used to find if an object is
(A) charged (B) magnetic (C) free of cracks (D) hot
18. A crack that occurs between tectonic plates
(A) Fault (B) Tremor (C) Focus (D) Epicentre
19. The method of charging an object by touching is called
(A) Induction (B) Diffusion (C) Conduction (D) Current
20. The boundaries of tectonic plates where earthquakes are most likely to occur?
(A) fault zone (B) epic zone (C) focus point (D) lithosphere
 Fill in the blanks
21. The instrument used to detect the presence of charge is called ________ .
22. Negatively charged objects will ________ positively charged objects.
23. Accumulation of ________ leads to lightening.
24. Highly destructive earthquakes have magnitudes greater than ________ on Richter scale.
25. The flow of heavy charge through air accompanied by heat and light is called ________.
 True or False
26. Tsunami is a Japanese word which means huge waves.
27. Tectonic plates cover the land, not the water.
28. Electric charges can be measured in coulombs.
29. Charges can flow through non-conductors.
30. The plates of the outermost layer of the earth are always in continuous motion.
31. Sitting on motor cycle is safe during lightning.
32. The process of electric discharge cannot occur between clouds and the earth.

 Solve the following
33. What happens when amber is rubbed with fur?
34. Explain static electricity?
35. Match the following.
Column 1
a) Richter scale
b) Waves
c) Lightning rod
d) Charge
Column 2
p) Protect house
q) Seismograph
r) Earthquake
s) Electroscope
36. Mention some safe places during thunderstorm.
37. What is lightning? How is it useful?
38. Who developed the idea of using lightning conductors to protect tall buildings?
39. What are the fault zones? Name some fault zones in India.
40. Explain the construction and working of an electroscope.
41. Write the mechanism of thunderstorms.
42. Is it possible to predict the occurrence of an earthquake?
43. If air and cloud were good conductors of electricity, do you think lightning could occur? Explain.
44. Describe the scale commonly used to measure the magnitude of earthquakes.
45. In an electroscope if a negatively charged body is brought in contact with the metal clip, the strips of the
electroscope diverge. If now another charged object carrying equal amount of positive charge is brought
in contact with the clip, what will happen?
46. Mention three precautions that you will take to protect yourself if earthquake strikes when you are inside
the house.
47. Detail out the structure of earth with a neat diagram.
48. Which metal can be used, instead of copper to make plate, which is buried deep in the earth?
49. Explain a) tectonic plates, b) seismic waves and c) epicenter.
50. What do you mean by earthing? What is its significance?
51. During the construction of a building the lightning conductor was left hanging in the air by mistake.
Would the lightning conductor be still effective? Explain.
52. The charge of an object is given by Q = ne, here n is the number of electrons and e is the electronic
charge (-1.6  10-19
C). If an object has charge -5  10-19
C, what should be the number of excess
electrons on it?
53. What are the effects of earthquake?
54. If a charged plastic straw is brought near another uncharged plastic straw, what will happen?
55. What are the different methods of charging a body? Explain them with neat diagrams.

56. How can charging take place when two substances are rubbed? Demonstrate it with an experiment.
57. How are earthquakes measured? Explain.
58. If the materials used for constructing a building were good conductors, do you think lightning will strike
the building. Will the lightning conductor be still required to be installed in the building?
59. Explain why it is safer to use a wireless telephone instead of a landline telephone during lightning.
60. Match the following.
Column 1
a) Magnitude
b) Tall buildings
c) Electric current
d) Tectonic plates
Column 2
p) Lithosphere
q) Lightning
r) Flow of charges
s) Richter scale
61. If the metal clip used in the electroscope is replaced by an ebonite rod and a charged body is brought in
contact with it, will there be any effect on the aluminium strips? Explain.
62. Plastic straws A and B are rubbed with dry cotton cloth. What will happen if they are brought near each
other?
63. You might have observed on a dry day that when you touch the screen of a television or computer
monitor (with picture tube), you get a slight shock. Why does it happen?
64. Explain the process of lightning striking a building? How can the building be protected?
65. What preventive steps should be taken to minimize the effects of earthquake in future?
66. How many types of charges are possible in nature?
******

Answers
1. (C) 2. (A) 3. (B) 4. (A) 5. (D) 6. (D)
7. (D) 8. (B) 9. (B) 10. (B) 11. (C) 12. (A)
13. (D) 14. (A) 15. (B) 16. (D) 17. (A) 18. (A)
19. (C) 20. (A)
21. electroscope 22. attract 23. charges 24. 7
25. lightning
26. True 27. False 28. True 29. False 30. True
31. False 32. False
33. attracts light objects 35. a-r, b-q, c-p, d-s 38. Benjamin Franklin 42. No
48. Silver 51. No 52. 3 54. attract each other
58. No 60. a-s, b-q, c-r, d-p 62. repel each other 66. 2
******

Additional Notes for Competitive Exams
LIGHTNING
Lightning is a bright flash of electricity produced by a thunderstorm. All thunderstorms produce lightning and
are very dangerous. If you hear the sound of thunder, then you are in danger from lightning.
What causes lightning?
Lightning is an electric current. Within a thundercloud many small bits of ice (frozen raindrops) bump into each
other or collide as they move around in the air. Those collisions create an electric charge. After a period of time,
the whole cloud fills up with electrical charges. The positive charges, or protons, form at the top of the cloud
and the negative charges, or electrons, form at the bottom of the cloud. Since opposites attract, that causes a
positive charge to build up on the ground beneath the cloud. The ground’s electrical charge concentrates around
anything that sticks up, such as mountains, people, or single trees. The charge coming up from these points
eventually connects with a charge reaching down from the thundercloud and lightning strikes. As storms
develop, clouds become charged with electricity. When voltage becomes high enough for the electricity to leap
across the air, lightning flashes. Lightning can strike within a cloud, from one cloud to another, from a cloud to
the ground, or from the ground to a cloud.
Ice in a cloud seems to be a key element in the development of lightning. Storms that fail to produce quantities
of ice may also fail to produce lightning. In a storm, the ice particles vary in size from small ice crystals to
larger hailstones, but in the rising and sinking motions within the storm there are a lot of collisions between the
particles. This causes a separation of electrical charges. Positively charged ice crystals rise to the top of the
thunderstorm, and negatively charged ice particles and hailstones drop to the middle and lower parts of the
storm. Enormous charge differences (electrical differential) develop.

EARTHQUAKE RELATED QUESTIONS
What is an earthquake?
Earthquake is the vibration of earth due to a rapid release of energy. Energy is released because of the rapid
movement on a fault.
What is a fault?
Fault is a fracture on which the tectonic plate movement has occurred. Rapid movement of 1 to 10 meters is
typically necessary to generate a significant earthquake. Faults are distinguished as dip-slip or strike-slip faults.
What is a seismogram?
The record of an earthquake at a seismograph station is a seismogram. The difference in arrival time between P
and S waves on a seismogram can be used to determine the distance of the station from the earthquake source.
Furthermore, the amplitude (height) of the S wave recorded at the station can be used to determine earthquake
magnitude.
What are the principal effects of an earthquake?
 Ground shaking: Rapid horizontal movements associated with earthquakes. Shaking is exaggerated in
areas where the underlying sediment is weak or saturated with water.
 Fault uplift: Large sections of the earth’s surface (thousands of square kilometers) may change elevation as
a result of uplift on an earthquake fault. Liquefaction occurs when water-saturated sediments collapse due
to violent shaking.
 Landslides: Earthquakes are often associated with mountains formed along convergent plate boundaries.
The steep slopes present in these environments are prone to landslides when shaken.
 Tsunamis: These are giant sea waves generated by submarine earthquakes, especially noted from the
Pacific Ocean.
What is the difference between great, major and strong earthquakes?
Great, major and strong earthquakes are differentiated by Richter magnitude. Great earthquakes (magnitude 8+)
are rare (average 1 per year); an average of 18 major earthquakes occur annually with a magnitude of 7 to 7.9;
strong earthquakes are more common (120 per year) with a magnitude of 6 to 6.9.
What are the constituents of a seismic wave?
P waves - P stands for primary. These waves arrive
first and move with a push-pull motion.
S waves - S stands for secondary. These waves arrive
second and move with a side-to side motion.
Surface waves - slowest and cause the most damage.
Move with an up and down and side-to side motion.

Locating an epicenter
You need at least 3 seismic stations to locate an epicenter. The P and S waves help determine where the
epicenter is located. Where all three circles meet is the location of the epicenter. The farther you are from the
epicenter, the greater is the S-P interval (the time between when the P wave hits and the S wave hits).
Locating an epicentre
******

Worksheet 1
1. How can an object be charged? Give two methods.
2. Answer the following.
(a) What is a gold leaf electroscope?
(b) List two uses of gold leaf electroscope.
(c) Draw a labelled diagram of a gold leaf electroscope.
(d) How does a gold leaf electroscope work?

Worksheet 2
1. Give reasons for the following.
(a) Lightning
(b) Earthquake
(c) Lightning conductors are used in the buildings.
(d) Seismograph is used to measure the intensity of earthquake.
(e) During earthquake, take cover under a heavy table.
(f) One should not take bath during lightning.
(g) Avoid being under the trees during lightning.

Answers
Worksheet 1
1. Object can be charged by friction and conduction.
2. (a) The gold leaf electroscope is used to measure the charge and also used to find out the nature of the
charge. The gold leaf electroscope has a metal disc attached to a metal rod. This rod passes into a bell
jar through a tightly fitted rubber stopper. Two metal thin strips are fixed at the bottom of the metal rod
made up of copper, brass or gold. The base of the jar has tin foils attached and the electroscope rests on
the wooden base.
(b) To measure the charge: The amount of divergence of the leaves is a measure of the amount of
charge in the body.
To find out the nature of the charge: This is possible only when the electroscope is charged with a
known charge. If the charges are same, the gold leaf will show divergence.
(c) Golden leaf electroscope
(d) To test whether a body has a positive or a negative charge: Take a charged object and touch the
charged electroscope. If the gold leaves diverge, the body is charged. Touch the disc with negatively
charged ebonite rod. The leaves get negatively charged and diverge.
Now bring the body with an unknown charge close to the disc. Observe the divergence. If the
divergence increases, then the body has similar charge. If the leaves collapse then the body has opposite
charge.
Worksheet 2
1. (a) During a thunderstorm, there is movement of clouds and air currents. The positive charges are
above the clouds and negative charges are below the clouds. There are positive charges on the ground
too. When a large amount of charges accumulate, the air is unable to stop the negative charges from
moving towards the positive charges on the earth. The charges meet, producing streaks of light and
sound. These streaks of light are called electric discharges.

(b) Earthquake tremors are caused due to the shifting of earth plates below the earth crust. The earth
layers are not in one piece; they are broken into fragments.
(c) Lightning conductors are devices used to protect the buildings. These are the rods installed above
the building which extend and are buried underground, so that at the time of lightning the charges gets
transferred to the ground through them.
(d) Seismograph is a simple vibrating rod or a pendulum, which starts vibrating when the tremor
occurs. A pen is attached to the vibrating system, which records the seismic waves on the paper which
moves under it. When the scientists study these waves, they are able to construct a complete map of the
earthquake and can also estimate the power that caused destruction.
(e) During earthquake, one should take cover under a heavy table so that he or she can be saved from
harm of life.
(f) Water is a good conductor of electricity so one should not take bath during lightning.
(g) Avoid being under the trees because they are not safe as lightning may fall on them.
******

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