GSEB Class 8 Science Solutions Chapter 15 Some Natural Phenomena

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Question 1. Which of the following cannot be changed easily by friction?
(a) A plastic scale
(b) A copper rod
(c) An inflated balloon
(d) Woolen cloth.
Answer: (b) A copper rod.
In simple words: A copper rod is a metal and a good conductor. It does not easily build up static electricity when rubbed, unlike insulators such as plastic or wool.

Exam Tip: Remember that conductors allow charges to move freely and thus don't easily get charged by friction, while insulators tend to hold static charges.

Question 2. When a glass rod is rubbed with a piece of silk cloth the rod:
(a) and the cloth both acquire a positive charge.
(b) becomes positively charged while the cloth has a negative charge.
(c) and the cloth both acquire a negative charge.
(d) becomes negatively charged while the cloth has a positive charge.
Answer: (b) becomes positively charged while the cloth has a negative charge.
In simple words: When a glass rod and silk cloth are rubbed, the glass rod gives away electrons to the silk. This makes the glass rod positively charged and the silk cloth negatively charged.

Exam Tip: Recall the triboelectric series to understand which material tends to lose electrons (become positive) and which gains electrons (become negative) when rubbed together.

Question 3. Write T against true and 'F' against false in the following statements:
(a) Like charges attract each other.
(b) A charged glass rod attracts a charged plastic straw.
(c) The lightning conductor cannot protect a building from lightning.
(d) Earthquakes can be predicted in advance.
Answer:
(a) False
(b) True
(c) False
(d) False
In simple words: Similar charges push each other apart, while a positively charged glass rod will attract a negatively charged plastic straw. Lightning conductors are designed to protect buildings, and earthquakes are currently impossible to predict.

Exam Tip: Understand the basic principles of electrostatics (attraction/repulsion of charges) and the purpose of lightning conductors. Also, know that earthquake prediction is not yet scientifically possible.

Question 4. Sometimes a crackling sound is heard while taking off a sweater during winters. Explain.
Answer: The electric discharge happens between the body and the sweater. During this discharge, some energy is given out. In this situation, energy is released as a crackling sound.
In simple words: Static electricity builds up when rubbing the sweater against your body. When you take it off, these charges quickly jump, creating small sparks and a crackling sound.

Exam Tip: This phenomenon is due to static electricity, where charges build up on surfaces and then discharge, often producing light (sparks) and sound.

Question 5. Explain why a charged body loses its charge if we touch it with our hand.
Answer: When we make contact with a charged body, it loses its electrical charge because of the earthing process. Our body is a good conductor of electricity. It moves the charges to the earth.
In simple words: When you touch a charged object, your body, being a conductor, provides a path for the electrical charges to flow into the ground, causing the object to lose its charge.

Exam Tip: Human bodies are good conductors of electricity, allowing charges to neutralize when they come into contact with charged objects, a process known as earthing or grounding.

Question 6. 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?
Answer: The scale used to measure earthquakes is the Richter Scale. Yes, an earthquake measuring 3 on the Richter Scale would be recorded by a seismograph. However, it is not likely to cause much damage.
In simple words: Earthquakes are measured using the Richter Scale. A magnitude 3 earthquake will be detected by a seismograph but is usually too weak to cause significant damage.

Exam Tip: Understand that the Richter Scale is logarithmic, meaning each whole number increase represents a tenfold increase in amplitude and about 32 times more energy released. Lower magnitudes are common and cause little to no harm.

Question 7. Suggest three measures to protect ourselves from lightning.
Answer: Three important measures for protection are:

• Stay under a covered area or inside a room.
• We should avoid using a TV or phone during lightning.
• We should not take a bath during lightning.

Exam Tip: Lightning seeks the path of least resistance. Avoid being the tallest object, and stay away from conductive materials or water during a thunderstorm.

Question 8. Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another uncharged balloon.
Answer: A charged balloon gets pushed away by another charged balloon because both balloons possess the same type of electrical charges. We understand that similar charges push each other apart. If one balloon is charged and the other is not, they do not have the same charge. Consequently, a charged balloon pulls an uncharged balloon towards it.
In simple words: Balloons with the same charge repel each other, pushing away. A charged balloon can attract an uncharged balloon because it induces opposite charges on its surface, drawing them together.

Exam Tip: Remember the fundamental rules of electrostatics: like charges repel, and unlike charges attract. Also, charged objects can induce charges in neutral objects, leading to attraction.

Question 9. Describe with the help of a diagram an instrument that can be used to detect a charged body.
Answer: An electroscope is used to find out if a body has an electrical charge or not. It works based on the rule that like charges push each other away, while unlike charges pull each other close. When the metal strips move apart, it shows that the body is charged because repulsion is the best way to prove if a body has a charge or not.

In simple words: An electroscope uses thin metal leaves inside a glass jar. If you touch its top with a charged object, the leaves gain the same charge, push apart, and show that the object is charged.

Exam Tip: Draw the electroscope clearly, labeling the key parts: metallic knob, metal rod, and gold/metal leaves. Explain that the divergence of leaves indicates the presence of a charge.

Question 10. List three states in India where earthquakes are more likely to strike.
Answer: Some states in India where earthquakes are more common include:

• Kashmir
• Rajasthan
• Gujarat
• Punjab

Exam Tip: Identify states located in active seismic zones, often near plate boundaries or fault lines, as these are more prone to earthquakes.

Question 11. Suppose you are outside your home and an earthquake strikes. What precautions would you take to protect yourself?
Answer: If an earthquake happens while you are outside your house, here are some safety steps:

• We should move to an open space.
• We should avoid taking shelter under trees or buildings.
• If we are driving, we should slow down the vehicle and move gently away from that area to a safe spot.

Exam Tip: Prioritize moving to an open, clear area during an outdoor earthquake to avoid falling debris from buildings, trees, or power lines.

Question 12. 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.
Answer: No, we will not carry an umbrella during a thunderstorm. Holding an umbrella will increase the danger from lightning. Tall objects are more likely to be hit by lightning strikes.
In simple words: It is not advisable to carry an umbrella during a thunderstorm. An umbrella's metal parts and its elevated position can make you a more attractive target for lightning, increasing your risk.

Exam Tip: During a thunderstorm, avoid holding tall or metallic objects, as they can act as conductors and increase your risk of being struck by lightning.