NCERT Class VIII Science Solutions: Chapter 15-Some Natural Phenomena Part 1

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Question 1:

Which of the following cannot be charged easily by friction?

  1. A plastic scale

  2. A copper rod

  3. An inflated balloon

  4. A woolen cloth.

Answer:

B. A copper rod

Question 2:

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

  1. And the cloth both acquire positive charge.

  2. Becomes positively charged while the cloth has a negative charge.

  3. And the cloth both acquire negative charge.

  4. Becomes negatively charged while the cloth has a positive charge.

Answer: B

When an object is charged by rubbing it against another object, the two objects get oppositely charged.

By convention, it is considered that the charged acquired by the glass rod is positive and charged acquired by the cloth is negative.

Glass happens to lose electrons easily, and silk grabs them away from the glass atoms, so after rubbing the glass becomes positively charged and the silk becomes negatively charged.

Question 3:

Write T against true and F against false in the following statements:

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

  2. A charged glass rod attract a charged plastic straw (T/F)

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

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

Answer:

  1. Like charges attract each other (False)

  2. A charged glass rod attract a charged plastic straw (True)

  3. Lightning conductor cannot protect a building from lightning (False)

  4. Earthquakes can be predicted in advance (False)

Question 4:

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

Answer:

Normally, Sweater is made of wool and the other inner clothes like shirts are made up of cotton and synthetic fibres. Due to friction among these, static charge gets accumulated on the sweater. While taking off sweater, an electric discharge occurs between sweater and the body which results in forming of sparks and crackling sound.

Image result for sweater

Sweater

Image result for sweater

Question 5:

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

Answer:

Human body is a good conductor of electricity. A charged body loses its charge when we touch it with hand because the charges get transferred through our body to earth. This process of transferring of charges from charged body to earth is known as earthling.