Some Natural Phenomena
Class 8th Science CBSE Solution
- Which of the following cannot be charged easily by friction? (a) A plastic scale (b) A…
- When a glass rod is rubbed with a piece of silk cloth the rod (a) and the cloth both…
- Write T against true and F against false in the following statements. (a) Like charges…
- Sometimes, a crackling sound is heard while taking off a sweater during winters. Explain.…
- Explain why a charged body loses its charge if we touch it with our hand.…
- Name the scale on which the destructive energy of an earthquake is measured. An earthquake…
- Suggest three measures to protect ourselves from lightning.
- Explain why a charged balloon is repelled by another charged balloon whereas an uncharged…
- Describe with the help of a diagram an instrument which can be used to detect a charged…
- List three states in India where earthquakes are more likely to strike.…
- Suppose you are outside your home and an earthquake strikes. What precaution would you…
- The weather department has predicted that a thunderstorm is likely to occur on a certain…
Exercises
Question 1.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
Answer:
The correct answer is option (b) A copper rod.
Because copper is a metal.
Question 2.
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.
Answer:
The correct answer is option (b) becomes positively charged while the cloth has a negative charge.
The rod is made from metal and metals loose electrons to become positively charged.
Question 3.
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)
Answer:
(a) The correct answer is False.
(b) The correct answer is True
(c) The correct answer is False
(d) The correct answer is False
Question 4.
Sometimes, a crackling sound is heard while taking off a sweater during winters. Explain.
Answer:
Sweater is made of wool and generally shirt we wear is a combination of cotton with some synthetic fibers. The rubbing of sweater and the shirt causes a friction between the shirt and sweater. This results in building up of electric charge. When enough charge has been accumulated, while taking off the sweater it discharges and transfer of electrons take place through air in the forms of spark and sound energy is released. Thus, we hear the crackling sound
Question 5.
Explain why a charged body loses its charge if we touch it with our hand.
Answer:
When we touch a charged body, with our hand, the excess of accumulated charge or static charges on it, gets transfer to ground through our body. Thus, the charged body loses its charge, and becomes neutral in nature i.e. neither positively charged nor negatively charged.
Question 6.
Name the scale on which the destructive energy of an earthquake is measured. An earthquake measure 3 on this scale. Would it be recorded by a seismograph? Is it likely to cause much damage?
Answer:
The magnitude or the intensity of an earthquake is measured on Richter Scale.
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. Generally, earthquake of magnitudes higher than 5 is considered destructive in nature.
Question 7.
Suggest three measures to protect ourselves from lightning.
Answer:
The three Protective measures against lightning are:
1) Stay indoors or under some covered area because lightening is dangerous.
2) Do not take bath during lightning.
3) Do not use any electrical appliances during lightning.
Question 8.
Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?
Answer:
A charged balloon is repelled by another charged balloon because both carry same charges and we know same charges repel each other. But a neutral body and a charged body (whether positively charged or negatively charged) attract each other. Therefore, an uncharged balloon is attracted by charged balloon.
Question 9.
Describe with the help of a diagram an instrument which can be used to detect a charged body.
Answer:
An electroscope can be used to detect whether a body is charged or not. The following figure shows a simple electroscope.
The copper wire receives the charge which is passed to the aluminium foil placed inside the glass jar. The aluminium foil strips receive the same charge from the charged copper wire. The strips carrying similar charges repel each other and they become wide open. Such a device can be used to test whether an object is carrying charge or not. This device is known as electroscope.
Question 10.
List three states in India where earthquakes are more likely to strike.
Answer:
The three states in India where earthquakes are more likely to strike are Jammu and Kashmir, Gujarat, and Assam.
Question 11.
Suppose you are outside your home and an earthquake strikes. What precaution would you take to protect yourself?
Answer:
Some of the precautions are:
1) Try to move to an open space away from buildings, trees, etc.
2) If inside house or building, take shelter inside cupboard, under table etc.
3) If travelling in a bus or a car, then do not come out when an earthquake strikes. Ask the driver to drive in an open field.
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, one should not carry an umbrella in a thunderstorm. During thunderstorms, which are accompanied with lightning, electric discharge from the clouds can travel through the metallic rod of the umbrella. This may give an electric shock to the person who is carrying it. Hence, it is not safe to carry an umbrella during lightning. Avoid going out of home if the weather department has already made predictions.