BASIC SCIENCE SOLUTION CLASS 8 CHAPTER 10 Electricity and Lightning

 

Exercise 

A. Answer the following in not more than 20 words. 

     What would you expect in the following cases?

(a) A plastic ruler is rubbed vigorously with a woollen cloth.

(b) A glass rod rubbed with a piece of silk is brought near a negatively charged paper cylinder. 

(c) A positively charged rod is moved slowly towards an uncharged paper cylinder, which is suspended by a string, until the rod touches the cylinder.

(d) A negatively charged body is brought in contact with the disc of a positively charged electroscope. 

(e) Someone touches the disc of a negatively charged electroscope.

B. Answer the following in not more than 40 words.

1. Explain how a piece of Styrofoam gets charged when it is rubbed with a piece of paper.

2. When a charged rod is moved towards an uncharged paper cylinder suspended by a string, the cylinder gets attracted to the rod initially, and then moves away with a jerk. Explain why. 

3. Why do the leaves of a gold-leaf electroscope diverge when a charged body is brought in contact with its disc? Do they always diverge to the same extent? 

4. What happens to the charge on an electroscope when its disc is connected to that of an uncharged electroscope with the help of a conducting wire? What happens to the leaves of the two electroscopes?

5. What are lightning conductors?

C. Answer the following in not more than 100 words.

1. Mention three ways by which a body can be charged. Describe an activity to illustrate how a body can be charged by induction. What would happen if you moved the rod away before separating the spheres?

2. With the help of a diagram, describe a gold-leaf electroscope.

3. How would you use an electroscope to determine the nature of the charge (positive or negative) on a body?

4. How does lightning occur?

D. Choose the correct option in each of the following

1. When two bodies are rubbed against each other. 

(a) they acquire equal and opposite charges

(b) they acquire similar charges

(c) one body acquires a charge and the other remains uncharged 

(d) they acquire different amounts of charge

2 When a negatively charged rod is brought close to two metal spheres which are in contact with each other, and the spheres are separated in the presence of the rod.  

(a) the sphere close to the rod acquires a negative charge and the other sphere acquires a positive charge

(b) the two spheres acquire the same charge

(c) the sphere close to the rod acquires a positive charge and the other sphere acquires a negative charge

(d) both spheres remain uncharged 

3. Which of the following statements is true?

(a) A charged body attracts an uncharged body, but repels a charged body.

(b) A charged body repels a body carrying a similar charge, but attracts a body carrying the opposite charge, as well as a body carrying no charge. 

(c) A charged body attracts another charged body, but repels an uncharged body.

(d) A charged body attracts another body, irrespective of whether it is charged or uncharged

4. A gold-leaf electroscope can be used

(a) only to detect a charge

(b) only to find the nature of a charge

(c) only to measure a charge

(d) to detect, measure and find the nature of a charge

5. If a plastic ruler is used to connect the disc of a charged electroscope, A, with that of an uncharged electroscope, B, the

(a) divergence of the leaves of A decreases 

(b) divergence of the leaves of A remains the same

(c) leaves of B also diverge

(d) divergence of the leaves of A increases

6. When an uncharged body touches a charged body, the 

(a) uncharged body acquires a similar charge

(b) uncharged body acquires an equal and opposite charge

(c) charged body loses its charge

(d) uncharged body remains uncharged

7. Charge flows from a charged body to an uncharged one 

(a) until the entire the charge from one flows into the other

(b) until they both carry the same charge

(c) until they both become uncharged

(d) continuously

E. Complete the following.

1. Electrons carry                   charge.

 2. While testing for charge,            is used as a proof for charge.

3. The force with which two similar charges repel each other depends on the.            of charge they carry.

4. The flow of charge through air or a gas is called an                      

5. A lightning conductor allows charge to harmlessly flow to the                    

Answer

A. 

(a) The plastic ruler becomes negatively charged due to the transfer of electrons from the cloth. 

(b) The paper cylinder becomes negatively charged due to induction. 

(c) The paper cylinder acquires a positive charge due to induction, and then the charge is neutralized by the rod. 

(d) The leaves of the electroscope diverge further due to the increase in the charge. 

(e) The leaves of the electroscope collapse due to the neutralization of the negative charge by the person. 

B. 

1. Electrons are transferred from the paper to the Styrofoam, leaving the Styrofoam negatively charged. 

2. The cylinder acquires a temporary opposite charge due to induction, but when the rod touches it, the charges neutralize and the cylinder becomes neutral. 

3. The charged body transfers some of its charge to the electroscope, causing the leaves to diverge. The extent of divergence depends on the amount of charge transferred. 

4. The charge on the electroscope distributes equally between the two electroscopes, causing their leaves to diverge equally. 

5. Lightning conductors provide a path for lightning to discharge safely into the ground. 

C. 

1. A body can be charged by friction, induction, or contact. To charge a neutral sphere by induction, bring a charged rod near it, but not touching it. Electrons will be induced to move, causing the sphere to acquire a charge. If the rod is moved away before the spheres are separated, the charge will redistribute itself and both spheres will remain uncharged. 

2. A gold-leaf electroscope consists of a metal rod attached to a metal disc, which is connected to two thin gold leaves. 

3. To determine the nature of the charge on a body, bring it near the electroscope. If the leaves diverge, the body has the opposite charge to the electroscope. 

4. Lightning occurs due to the buildup of static charge in storm clouds, which can discharge as a bolt of lightning. 

D. 

1. (c) one body acquires a charge and the other remains uncharged 

2. (a) the sphere close to the rod acquires a negative charge and the other sphere acquires a positive charge 

3. (b) A charged body repels a body carrying a similar charge, but attracts a body carrying the opposite charge, as well as a body carrying no charge. 

4. (d) to detect, measure and find the nature of a charge 

5. (b) divergence of the leaves of A remains the same 

6. (b) uncharged body acquires an equal and opposite charge 

7. (b) until they both carry the same charge 

E. 

1. negative 

2. electroscope 

3. magnitude 

4. electric discharge 

5. ground

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