NCERT Solution For Class 8 Science, Chapter 15 – Some Natural Phenomena

NCERT Solutions is known as an extremely helpful resource for preparing for the exam. Takshila Learning provides its learners with access to a wealth of NCERT problems and their solutions. CBSE Class 8 Science NCERT Solutions are built by subject matter experts, so be sure to train learners for a good grade. The questions set out in the NCERT Books are prepared in compliance with the requirements of the CBSE.

NCERT Solution For Class 8 Science – The Indian Constitution provides us with all-inclusive information on all concepts. As students would have to learn the basics about the subject in class 8, this curriculum for class 8 is comprehensive study material, which explains the concepts in a great way.

Q1. Which of the following cannot be charged easily by friction?

(a)        A plastic scale

(b)        A copper rod

(c)        An inflated balloon

(d)        A woollen cloth

Solution:

(b) A copper rod

Copper is a highly conducting materials. Only non-conducting materials can be easily charged by friction. Hence, a copper rod cannot be charged easily by friction.

Q2. When a glass rod is rubbed with a piece of silk cloth the rod

(a) and the cloth both acquire positive charge.

(b) becomes positively charged while the cloth has a negative charge.

(c) and the cloth both acquire negative charge.

(d) becomes negatively charged while the cloth has a positive charge.

Solution:

(b) The rod becomes positively charged, while the cloth has a negative charge.

When an object is charged by rubbing it against another object, the two objects get oppositely charged. By convention, it is considered that the charge acquired by the glass rod is positive and charge acquired by the cloth is negative. Due to this, the rod becomes positively charged and the cloth becomes negatively charged.

Q3. Write T against true and F against false in the following statements.

(a)        Like charges attract each other. (T / F)

(b)        A charged glass rod attracts a charged plastic straw. (T / F)

(c)        Lightning conductor cannot protect a building from lightning. (T/F)

(d)        Earthquakes can be predicted in advance. (T / F)

Solution:

(a) False

Like charges repel each other and the unlike charges that attract each other.

(b) True

A charged glass rod has positive charges on its surface while a charged plastic straw has negative charges on its surface. As we know, unlike charges attract each other, a charged glass rod attracts a charged plastic straw.

(c) False

During a lightning, the lightning conductor conducts all the atmospheric charges to the Earth directly, leaving the building safe. In this way, lightning conductors protect a building from lightning.

(d) False

Although the causes of earthquakes are known, but no instrument could be invented to detect it till now. Therefore, earthquakes cannot be predicted in advance.

Q4. Sometimes, a crackling sound is heard while taking off a sweater during winters. Explain.

Solution:

When a sweater is taken off, the woollen sweater gets charged due to the friction between the sweater and the body. So, one can hear a crackling sound during the given process.

Q5. Explain why a charged body loses its charge if we touch it with our hand.

Solution:

When we touch a charged object, our body conducts its charges to the earth. In this why a charged body loses its charge, if we touch it with our hand. This phenomenon is called electric discharge.

Q6. 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:

The destructive energy of an earthquake is measured by the Richter scale. It has scale for readings from 1 to 10.

The reading of magnitude 3 on the Richter scale would be recorded by a seismograph.

If the Richter scale gives a reading of magnitude 3, then the earthquake is not likely to cause much damage as generally, earthquake of magnitudes higher than 5 is considered destructive in nature.

Q7. Suggest three measures to protect ourselves from lightning.

Solution:

Protective measures against lightning are as follows:

(i)         Stay in a completely closed place.

(ii)        Do not touch any electrical wires, telephone cables, metal pipes, etc.

(iii)       Do not bath in running water as it may cause an electric shock.

Q8. Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?

Solution:

The nature of charges present on the surface of charged balloons are similar. As like charges repel each other, two charged balloons repel each other. When a charged body is brought near an uncharged body, the uncharged body acquires charges on its surface caused by the induction of charges. The charges are of opposite nature in relation to the charged body. As unlike charges attract each other, a charged body always attracts an uncharged body. Therefore, an uncharged balloon is attracted by another charged balloon.

Q9. Describe with the help of a diagram an instrument which can be used to detect a charged body.

Solution:

An electroscope can be used to detect whether a body is charged or not. The following figure shows a simple electroscope.

It consists of a metal rod. At one end of the rod, two leaves of foil are fixed and at the opposite end, there’s a metal disc. The leaves of foil are placed inside a conical flask and also the flask is corked to isolate the leaves from air.

When the metal disc is touched with a charged body, the aluminium strips move away from one another. This happens because some of the charges of the body are transferred to the strips through the metal rod. This method of charging a body is termed charging by conduction. The nature of charges on both the leaves and also the charged body are the similar. Hence, both the leaves of the foil will move away from one another. If the body wasn’t charged, then the leaves of the foil would remain as they were before and they’d not repel one another.

Q10. List three states in India where earthquakes are more likely to strike.

Solution:

The three states in India where earthquakes are more likely to strike are Jammu and Kashmir, Gujarat , and Assam.

Q11. Suppose you are outside your home and an earthquake strikes. What precaution would you take to protect yourself?

Solution:

Some of the precautions are as follows:

(i)         Try to find an open field far from tall buildings, installations, tall trees, and electric wires and poles.

(ii)        If travelling in a bus or a car, then don’t commence when an earthquake strikes. Ask the driver to drive in an open field.

Q12. 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:

No. we should always not carry an umbrella in a thunderstorm. During thunderstorms, which are accompanied with lightning, electrical conduction from the clouds can travel through the metallic rod of the umbrella which could give an electrical shock to the one that is carrying it. So, it’s not safe to hold an umbrella during lightning.

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