Lakhmir Singh & Manjit Kaur: Some Natural Phenomena- 3 | Lakhmir Singh & Manjit Kaur Solutions: Class 8 Science PDF Download

Q.51. 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 woollen cloth

Correct Answer is option (b)

All of the above substances are insulators whereas Copper rod is a conductor. As soon as we charge a copper rod by rubbing with another material, the electric charge flow through our hand and body and flows into the earth. As a result, the copper rod remains un-charged.

Q.52. When a glass rod is rubbed with a piece of silk cloth, then:
(a) The glass rod and silk cloth both acquire positive charge.
(b) The glass rod becomes positively charged while the silk cloth has a negative charge.
(c) The glass rod and silk cloth both acquire negative charge.
(d) The glass rod becomes negatively charged while the silk cloth has a positive charge.

Correct Answer is option (b)

After rubbing the glass rod with silk cloth, the glass rod becomes positively charged. The silk cloth becomes negatively charged. The electric charges generated by rubbing are static electric charges. These electric charges remain bound on the surface of the charged object.

Q.53. Which of the following are transferred from one object to another when these two objects are charged by friction?
(a) Atoms
(b) Protons
(c) Neutrons
(d) Electrons

Correct Answer is option (c)

The electric charges generated by rubbing are static electric charges. There are two types of charges: Positive charge and negative charge.

Q.54. The electric nature of lightning was established by a scientist named:
(a) Isaac Newton
(b) Robert Hooke
(c) Benjamin Franklin
(d) Thales

Correct Answer is option (c)

Benjamin Franklin is the scientist who showed that lightening is electric in nature. He discovered many things about lightening and was the first to show that a thunderstorm lets out electricity.

Q.55. A plastic comb is rubbed with dry hair whereas a glass rod is rubbed with a piece of silk cloth. Which of these will get negatively charged?
(i) Plastic comb
(ii) Glass rod
(iii) Dry hair
(iv) Silk cloth
(a) A and B
(b) B and C
(c) A and D
(d) B and D

Correct Answer is option (c)

After rubbing the glass rod with silk cloth, the glass rod becomes positively charged. The silk cloth becomes negatively charged. When a plastic comb is dry hair, it becomes negatively charged. The negatively charged comb induces a positive charge on the pieces of paper which are neutral in nature.

Q.56. The magnitude of an earthquake is measured on:
(a) Celsius scale
(b) Kelvin scale
(c) Decibel scale
(d) Richter scale

Correct Answer is option (d)

The magnitude (or intensity) of an earthquake is expressed in terms of Richter scale. The destructive earthquakes have magnitudes higher than 7 on the Richter scale.

Q.57. An earthquake of magnitude 2 on Richter scale is:
(a) Two times as strong as an earthquake of magnitude 1
(b) Four times as strong as an earthquake of magnitude 1
(c) Ten times as strong as an earthquake of magnitude 1
(d) Hundred times as strong as an earthquake of magnitude 1

Correct Answer is option (c)

The magnitude (or intensity) of an earthquake is expressed in terms of Richter scale. The destructive earthquakes have magnitudes higher than 7 on the Richter scale.

Q.58. The epicentre of an earthquake is:
(a) Deep under the crust of earth
(b) In the mantle of earth
(c) On the surface of earth
(d) In the core of earth

Correct Answer is option (a)

Focus of an earthquake is located deep under the ground. Focus is the point inside the crust where the pressure is released. The point on the earth’s surface above the focus is called the epicenter.

Q.59. The waves generated by the earthquake tremors are called:
(a) Ultrasonic waves
(b) Rhythmic waves
(c) Systemic waves
(d) Seismic waves

Correct Answer is option (d)

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

Q.60. When an object gets negatively charged by the process of friction, then:
(a) The object loses some electrons
(b) The object loses some protons
(c) The object gains some electrons
(d) The object gains some protons

Correct Answer is option (c)

The electric charges generated by rubbing are static electric charges. There are two types of charges: Positive charge and negative charge.

Q.61. The device used for detecting charge (positive or negative) on an object is called:
(a) Stethoscope
(b) Telescope
(c) kaleidoscope
(d) Electroscope

Correct Answer is option (c)

Electroscope is the device which is used to detect charge on a body. It is used for detecting, measuring and finding the nature of a charge.

Q.62. A charged object attracts an uncharged object by producing opposite charges in the nearer end of the uncharged object by the process of:
(a) Electric potential
(b) Electric induction
(c) Friction
(d) Electromagnetic induction

Correct Answer is option (c)

The electric charges generated by rubbing are static electric charges. These electric charges remain bound on the surface of the charged object.

Q.63. A lightning conductor is a device which transfers:
(a) Eectric energy
(b) Light energy
(c) Solar energy
(d) Photoelectric energy

Correct Answer is option (b)

Lightening conductor is a device which is used to protect a tall building from lightening. A metallic rod, taller than the building, is installed in the walls of the building during its construction.

Q.64. When a plastic comb is rubbed with dry hair, the hair get positively charged by friction. In this porcess:
(a) The hair loses some positive protons
(b) The hair gain some positive protons
(c) The hair loses some negative electrons
(d) The hair gain some negative electrons

Correct Answer is option (b)

The combing of hair make the comb negatively charged. It is able to attract tiny pieces of paper which are neutral.

Q.65. Which of the following part of the earth is made up of molten iron?
(a) Mantle
(b) Inner core
(c) Outer core
(d) Crust

Correct Answer is option (b)

The outer core is the layer surrounding the inner core. It is a liquid layer. It is also made up of iron and nickel.

Q.66. Which of the following area of India is not the most threatened by earthquakes?
(a) North-East
(b) Kashmir
(c) West Bengal
(d) Rajasthan

Correct Answer is option (c)

The states in India where earthquakes are most likely to occur are Kashmir, Western and Central Himalayas, the whole of North-East, Rann of Kutch, Rajasthan and the Indo – Gangetic Plane.

Q.67. The place inside the earth’s crust where the earthquake is generated is called:
(a) Seismic zone of the earth
(b) Epicentre of the earthquake
(c) Fault zone of the earth
(d) Focus of the earthquake

Correct Answer is option (d)

Focus of an earthquake is located deep under the ground. Focus is the point inside the crust where the pressure is released. The point on the earth’s surface above the focus is called the epicenter.

Q.68. An inflated rubber balloon is rubbed with a woollen cloth whereas a ballpoint pen refill is rubbed with a polythene bag. Which of these will get positively charged?
(i) Inflated rubber balloon
(ii) Woollen cloth
(iii) Ballpoint pen refill
(iv) Polythene bag
(a) A and B
(b) B and C
(c) A and D
(d) B and D

Correct Answer is option (b)

A ballpoint pen refill can be charged by rubbing it against the wool cloth. It becomes negatively charged.

Q.69. Lightning can even burn up a tree. Lightning contains a tremendous amount of:
(a) Heat energy
(b) Electric energy
(c) Chemical energy
(d) Nuclear energy

Correct Answer is option (b)

Lightening is the name given to the flash of light which occurs in the sky during the rainy season. The process of electric discharge between clouds and the earth or between different clouds causes lightning.

Q.70. The tremendous electric charges in the atmosphere which produce sheet lightning in the clouds are produced by the process of:
(a) Friction
(b) Induction
(c) Conduction
(d) Convection

Correct Answer is option (a)

The process of electric discharge between clouds and the earth or between different clouds causes lightning.

Q.71. Explain why, a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by a charged balloon.

There are two types of charges: Positive charge and negative charge. Like charges repel each other and unlike charges attract each other. A charged balloon repels another charged balloon because like charges repel each other. A charged balloon attracts an uncharged balloon by the process of electric induction. The charged balloon produces opposite charges in the nearer end of the uncharged balloon.

Q.72. Explain why, a glass rod can be charged by rubbing when held by hand but an iron rod cannot be charged by rubbing, if held by hand.

The electric charges generated by rubbing are static electric charges. These electric charges remain bound on the surface of the charged object. When a glass rod is rubbed with silk, some of the electrons from the glass atoms are transferred to silk. Due to the deficiency of electrons in the glass atoms, it becomes positively charged. Whereas the silk has acquired electrons, it becomes negatively charged. Iron rod is a conductor. As soon as we charge an iron rod by rubbing with another material, the electric charge flow through our hand and body and flows into the earth. As a result, the iron rod remains un-charged by rubbing, if held by hand.

Q.73. A glass rod is rubbed with a silk cloth and an inflated rubber balloon is rubbed with a woollen cloth. Now, out of glass rod, silk cloth, rubber balloon and woollen cloth:
(a) which two objects acquire negative charge?
(b) which two objects acquire positive charge?

(a) Silk cloth and Rubber balloon acquire negative charge. When a glass rod is rubbed with silk, some of the electrons from the glass atoms are transferred to silk. Due to the deficiency of electrons in the glass atoms, it becomes positively charged. Whereas the silk has acquired electrons, it becomes negatively charged. An inflated rubber balloon can be charged by rubbing it against the woolen cloth. Upon rubbing, the wool loses electrons and it causes the electrons to move from the wool to the balloon’s surface. The rubbed part of the balloon now has a negative charge.
(b) Glass rod and Woolen cloth acquire positive charge. When a glass rod is rubbed with silk, some of the electrons from the glass atoms are transferred to silk. Due to the deficiency of electrons in the glass atoms, it becomes positively charged. An inflated rubber balloon can be charged by rubbing it against the woolen cloth. Upon rubbing, the wool loses electrons and it causes the electrons to move from the wool to the balloon’s surface. The woolen cloth is left with a positive charge.

Q.74. What will you observe when the metal top of an electroscope is touched with:
(a) a positively charged object?
(b) a negatively charged object?

(a) When a glass rod is rubbed with a silk cloth, it acquires positive charge. When it is touched with the metal top of an electroscope, both the metal top and leaves acquires a positive charge due to conduction. As a result of the positive charge on both the leaves, the divergence of leaves takes place.
(b) After rubbing the plastic comb, it acquires negative charge. When it is touched with the metal cap of an electroscope, both the metal cap and the leaves acquire negative charge due to conduction. As a result of negative charge on both the leaves, divergence of leaves takes place.

Q.75. An earthquake measures 3 on Richter Scale:
(a) Would it be recorded by a seismograph?
(b) Is it likely to cause much damage?

(a) Earthquake is the phenomenon in which the earth shakes suddenly for a very short time. It is caused by a disturbance deep inside the earth’s crust. Seismograph is the instrument which is used to measure and record an earthquake. The tremors produce waves on the surface of the earth. These are called seismic waves. These waves are recorded by the seismograph. Yes, An earthquake measuring 3 on Richter scale will be recorded by a seismograph.

(b) Earthquake is the destructive natural phenomenon which cannot be predicted in advance. The earthquakes can cause floods, landslides and tsunamis. Most earthquakes are caused by the movement of earth’s plates. The magnitude (or intensity) of an earthquake is expressed in terms of Richter scale. The destructive earthquakes have magnitudes higher than 7 on the Richter scale. No, an earthquake which measures 3 on Richter scale is unlikely to cause much damage.