Lakhmir Singh & Manjit Kaur: Some Natural Phenomena- 1 | Lakhmir Singh & Manjit Kaur Solutions: Class 8 Science PDF Download

Q.1. What are the two kinds of electric charges?

There are two types of charges: Positive charge and negative charge. Like charges repel each other and unlike charges attract each other.

Q.2. 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?

(a) After rubbing the glass rod with silk cloth, the glass rod becomes positively charged. The silk cloth becomes negatively charged.

(b) The plastic comb acquires negative charge when it is rubbed with dry hair.

Q.3. What type of electric charge is acquired by a rubber balloon when rubbed with a woolen cloth?

The rubber balloon becomes negatively charged when rubbed with a woolen cloth.

Q.4. A negatively charged object attracts another charged object placed near it. What is the nature of charge on the other object?

The nature of charge on the other object will be positive. This is because like charges repel each other and unlike charges attract each other.

Q.5. A positively charged object repels another charged object kept close to it. What is the nature of charge on the other object?

The nature of charge on the other object will be positive. This is because like charges repel each other and unlike charges attract each other.

Q.6. A negatively charged object repels another charged object held near it. What is the nature of charge on the other object?

The nature of charge on the other object is negative. This is because like charges repel each other and unlike charges attract each other.

Q.7. A glass rod is rubbed with a silk cloth. What type of charge is acquired by (a) silk cloth, (b) glass rod?

After rubbing the glass rod with silk cloth, the glass rod becomes positively charged. The silk cloth becomes negatively charged.

Q.8. An inflated rubber balloon and a woollen cloth are rubbed together. What type of charge is acquired by (a) woollen cloth, and (b) rubber balloon?

The rubber balloon becomes negatively charged when rubbed with a woolen cloth. The woolen cloth acquires a positive charge.

Q.9. Name the device to detect electric charge on a body.

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.10. When an object is touched with the metal top of an electroscope, its aluminium leaves diverge. What conclusion do you get from this observation?

If the leaves of the electroscope diverge or open up when an object is touched, the body is charged. The extent of divergence or opening up of the leaves is a measure of the charge on the body. A body with higher charge will cause greater opening up of the leaves.

Q.11. What name is given to the flash of light which occurs in the sky during the rainy season?

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.12. Why should a person not stand under a tree during a thunderstorm?

Trees are usually the tallest objects around and have many pointy tips. The electric field is strong near the pointed tips. The current from a lightening may leave the tree and jump over to the person standing near the tree. The current will then follow from the body of the person on its way to the ground.

Q.13. Name the scientist who showed that lightning is electric in nature.

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.14. Name the device which is used to protect a tall building from lightning.

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.15. What name is given to the phenomenon in which the earth shakes suddenly for a very short time?

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.

Q.16. Name one destructive natural phenomenon which cannot be predicted in advance.

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.

Q.17. List three states in India where earthquakes are more likely to occur.

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.18. Name the instrument used to measure and record an earthquake.

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.

Q.19. What was the magnitude of Bhuj and Kashmir earthquakes on the Richter Scale?

The magnitude of Bhuj and Kashmir earthquakes on the Richter Scale was more than 7.5 The destructive earthquakes have magnitudes higher than 7 on the Richter scale.

Q.20. Name the scale on which the magnitude (or intensity) of an earthquake is expressed.

There are a number of ways to measure the magnitude of an earthquake. But, the Richter magnitude scale (often shortened to Richter scale) is the most common standard of measurement for earthquakes.
The Richter scale is used to rate the magnitude of an earthquake, that is the amount of energy released during an earthquake.

Q.21. For what purpose is the Richter Scale used?

The Richter scale is used to measure the magnitude (or intensity) of an earthquake. It measures the power of an earthquake. The destructive earthquakes have magnitudes higher than 7 on the Richter scale.

Q.22. Name two events (other than earthquakes) which can cause tremors on the earth.

The tremors on the earth can be caused when a volcano erupts or when a meteor hits the earth. It can also be caused by an underground nuclear explosion.

Q.23. In the context of an earthquake, which one is deep under the ground: focus or epicentre?

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.24. State whether the following statements are true or false :
(a) Like charges attract each other.
(b) A charged glass rod attracts a charged plastic straw.
(c) Lightning conductor cannot protect a building from lightning.
(d) Earthquakes can be predicted in advance.
(e) An earthquake of magnitude 2 on Richter Scale is ten times as strong as an earthquake of magnitude 1 on the same Scale.
(f) The plates of earth’s crust are continuously moving.
(g) An earthquake is measured and recorded by using an instrument called electrocardiograph.

(a) This statement is False.

Like charges repel each other and unlike charges attract each other.
(b) This statement is True.

A charged glass rod has positive charge on its surface and a charged plastic straw has negative charge on its surface. The charges are opposite in nature and hence, they attract each other.
(c) This statement is False.

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.
(d) This statement is False.

An earthquake is a sudden shaking or trembling of the earth. It is caused by a disturbance deep inside the earth’s crust. It is not possible to predict the occurrence of an earthquake.
(e) This statement is True.

The Richter scale is used to measure the magnitude (or intensity) of an earthquake. It measures the power of an earthquake. The destructive earthquakes have magnitudes higher than 7 on the Richter scale.
(f) This statement is True.

The outermost layer of the earth is fragmented. Each fragment is called a plate. These plates are in continual motion. When they brush past one another, or a plate goes under another due to collision they cause disturbance in the earth’s crust that shows up as an earthquake on the surface of the earth.
(g) This statement is False.

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.

Q.25. Fill in the following blanks with suitable words:
(a) Like charges ______; unlike charges______
(b) Rubbing glass with silk makes a______charge on the glass.
(c) Combing your hair makes a______charge on the comb.
(d) The negatively charged particles which are transferred from one object to another during charging by friction are called______
(e) The charging of an object by rubbing it with another object is called charging by______
(f) In an electroscope, the aluminium leaves diverge because like charges______

(g) ______is provided in buildings to protect us from electric shocks due to any leakage of electric current.
(h) Lightning is nothing but an______spark.
(i) Each fragment of earth’s crust is called a______ 

(a) The correct Answer is ______ repel and ______ attract.
There are two types of charges: Positive charge and negative charge. Like charges repel each other and unlike charges attract each other.
(b) The correct Answer is ______ positive.

After rubbing the glass rod with silk cloth, the glass rod becomes positively charged. The silk cloth becomes negatively charged.
(c) The correct Answer is______ negative.

The combing of hair make the comb negatively charged. It is able to attract tiny pieces of paper which are neutral.
(d) The correct Answer is______ electrons.

For example, 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.
(e)The correct Answer is______ friction.

The electric charges generated by rubbing are static electric charges. These electric charges remain bound on the surface of the charged object.
(f) The correct Answer is______ repel.

The aluminium foil strips receive the same charge from the charged objects. The strips carrying similar charges repel each other and they become wide open.
(g) The correct Answer is______  Earthing.

The process of transferring charge from a charged object to the earth is called earthing.
(h) The correct Answer is______ electric.

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.
(i)The correct Answer is______ Plate.

The outermost layer of the earth is fragmented. Each fragment is called a plate. These plates are in continual motion.