Question 1

Question 2(c)Assertion (A) : Lightning is a natural example of static electricity.Reason (R) : Lightning occurs due to the accumulation of same charges in clouds and earth's surface.Both A and R are true and R is the correct explanation of ABoth A and R are true and R is not the correct explanation of AAssertion is true but reason is falseAssertion is false but reason is true

Accepted Answer

Assertion is true but reason is falseExplanationLightning indeed represents a large-scale electrostatic discharge, so the Assertion is correct.However, it is produced by the build-up of opposite charges—typically negative charges in the lower part of a cloud and positive charges on Earth’s surface or in another cloud—not by the build-up of like charges. Therefore the Reason is incorrect.

Question 2

Question 2(d)Assertion (A) : Conductors can be charged by friction.Reason (R) : Conductors allow charges to flow through them and do not retain static charges.Both A and R are true and R is the correct explanation of ABoth A and R are true and R is not the correct explanation of AAssertion is true but reason is falseAssertion is false but reason is true

Accepted Answer

Assertion is false but reason is trueExplanationFrictional charging is effective only for insulators. When a conductor is rubbed, any charge produced immediately moves through the material and leaks away to the surroundings (usually to the Earth) unless the conductor is completely insulated. Therefore the Assertion is false.The Reason correctly states that charges in a conductor are free to move, so a conductor does not easily hold static charge; hence the Reason is true and correctly explains why the Assertion is false.

Question 3

Question 2How will you show that like charges repel and unlike charges attract each other?

Accepted Answer

The following experiment demonstrates that like charges repel and unlike charges attract each other:Take a glass rod A1. Rub it with silk and suspend it with a thread. Take another glass rod B1. Rub it with silk and bring it near one end of the suspended rod A1. It is observed that the suspended glass rod A1 gets repelled.Take an ebonite rod A2. Rub it with fur and suspend it with thread. Take another ebonite rod B2. Rub it with fur and bring it near one end of the suspended rod A2. It is observed that the suspended ebonite rod A2 gets repelled.Suspend glass rod A1 rubbed with silk and bring ebonite rod B2 near one end of the suspended rod A1. It is observed that rod A1 gets attracted towards rod B2.In step 1, both the rods A1 and B1 were rubbed with silk, so, they must have similar kind of charges. Similarly, in step 2 also rods A2 and B2 must have similar kind of charges. As A1 and A2 got repelled by B1 and B2, respectively hence, we conclude that like charges repel each other. In step 3, A1 got attracted to B2 hence, we conclude that A1 and B2 are oppositely charged and unlike charges attract each other.

Question 4

Question 5An ebonite rod is rubbed with fur. Explain the charging of the ebonite rod and the fur on the basis of electron movement.

Accepted Answer

When an ebonite rod is rubbed with fur, the free electrons from the fur are transferred to the ebonite rod. The fur loses some electrons and it becomes positively charged. The ebonite rod gains the same number of electrons and it becomes negatively charged by an equal amount.

Question 5

Question 6Distinguish between conductors and insulators of electricity.

Accepted Answer

ConductorsInsulatorsSubstances which have large number of free electrons are called conductors.Substances which have very less number of free electrons or no free electrons are called insulators.They allow the electricity to flow through them.They do not allow the electricity to flow through them.They cannot be charged by rubbing.They can be charged by rubbing.Metals like silver, copper, aluminium etc. are conductors.Substances like wood, paper, glass, rubber etc. are insulators.

Question 6

Question 7Describe the method of charging a conductor by conduction.

Accepted Answer

In charging by conduction method, the conductor to be charged is touched or brought in contact with a charged body. The conductor gets charged by the similar kind of charge as on the charging body.Method of chargingSuppose we want to charge a metal rod A with a positive charge.Take the metal rod A and place it on an insulating stand.Take a positively charged glass rod B provided with an insulating handle and touch it with the metal rod A as shown in the figure below. Some positive charge of the glass rod B is shared by the metal rod A.Remove the glass rod B.The rod A gets positively charged.

Question 7

Question 8Explain the charging by conduction in terms of movement of electrons.

Accepted Answer

Suppose we want to positively charge a metal rod A. Place it on an insulating stand and touch it with a positively charged glass rod B. The rod A gets positively charged.Explanation in terms of movement of electrons — The glass rod B is positively charged so it has a deficiency of electrons. When it is touched with the metal rod A, the free electrons of the rod A move to the glass rod B. Due to loss of electrons in the rod A, it becomes positively charged.

Question 8

Question 9Describe the method of charging a conductor by induction.

Accepted Answer

Suppose we want to charge a metal rod A negatively, proceed as follows:Place the rod A on insulating stand.Take a positively charged glass rod B provided with an insulating handle.Bring it near the rod A.The near end P of the metal rod A will acquire negative charge while the far end Q acquires positive charge as shown in below figure.Now touch the end Q of rod A by hand. Then remove hand and glass rod B simultaneously.The rod A becomes negatively charged.

Question 9

Question 10Explain the charging by induction in terms of movement of electrons.

Accepted Answer

Suppose we want to charge a metal rod A negatively by induction. Bring a positively charged glass rod B near one end of rod A.The near end P of the rod A acquires negative charge and the far end Q acquires positive charge. The positively charged glass rod B attracts the free electrons from the end Q towards the end P of rod A. Thus, end P becomes negatively charged as it gains the electrons and end Q becomes positively charged as it loses the electrons.Now touch the end Q of rod A by hand and then remove hand and rod B simultaneously. The rod A becomes negatively charged.On touching the end Q of rod A, the free electrons move from earth to neutralize the positive charge at end Q. On removal of glass rod B and hand simultaneously, the negative charge at the end P gets distributed throughout the rod A making it negatively charged.

Question 10

Question 11Describe a pith ball electroscope. How can you use it to test whether a body is charged or uncharged?

Accepted Answer

Pith ball electroscope consists of a small pith ball suspended by a dry silk thread from an insulating stand.To test whether a body is charged or uncharged, bring the body near the pith ball without touching. If the pith ball moves towards the body, the body is charged. But if the pith ball remains stationary the body is uncharged.

Question 11

Question 12How will you use a pith ball electroscope to find out whether the charge on a charged body is positive or negative?

Accepted Answer

Using Pith ball electroscope, we can determine the type of charge on the body by following the below steps:.Take a charged pith ball electroscope. Let it be positively charged.Bring the charged body near the pith ball without touching it.If the pith ball moves away, the body has positive charge.If the pith ball moves towards the body, the body has negative charge.

Question 12

Question 13Draw a labelled diagram of a gold leaf electroscope and describe its construction.

Accepted Answer

Construction of gold leaf electroscope:A gold leaf electroscope consists of two gold or aluminium leaves hanging from a brass rod, having a brass disc at its upper end.The rod passes through an ebonite cork fitted in the mouth of a glass bottle.The glass bottle has tin foils on its sides near its bottom which are earthed.Figure of gold leaf electroscope:

Question 13

Question 14How will you use a gold leaf electroscope to find out whether a body is charged or uncharged?

Accepted Answer

Bring the body and touch it with the brass disc of the gold leaf electroscope. If the leaves diverge, the body is charged. But if the leaves do not diverge, the body is uncharged.

Question 14

Question 15How will you use a gold leaf electroscope to find out whether the charge on a charged body is positive or negative?

Accepted Answer

Gold leaf electroscope is used to detect the type of charge present in a charged body by the following method:Take a charged gold leaf electroscope (Suppose the electroscope is positively charged).Bring the charged body to be tested in contact with the brass disc of the electroscope.If divergence of leaves increases, the body has positive charge.If divergence of leaves decreases, the body has negative charge.For the case when electroscope is negatively charged, if divergence of leaves increases, then body is negatively charged and if it decreases then body is positively charged.

Question 15

Question 16Describe Franklin's experiment. What did he conclude from his experiment?

Accepted Answer

Franklin's experiment:Benjamin Franklin took a kite made of silk.At the top corner of the kite, he fixed a metal wire about 30 cm long.The other end of the wire was joined to a string.At the lower end of the string, he tied a metal key and then a silk strip. The silk strip acts as an insulating handle. He flew the kite in thunderstorm.Observation — He obtained a number of sparks between his knuckle and key when the string got wet.Conclusion — He concluded that during thunderstorm the clouds acquire an electric charge. Hence, with his kite experiment, he proved that lightning is a form of electricity.

Question 16

Question 17State three safety measures that you will observe in a thunderstorm.

Accepted Answer

The three safety measures that are observed during thunderstorm are:Do not stand under a tree or near a tall building.Do not carry an umbrella over your head particularly if walking in an open ground.Take out the plugs of TV sets, computers, etc. Do not use the wired phone.

Question 17

Question 18What causes lightning?

Accepted Answer

During a thunderstorm, when a charged cloud passes over the earth (or over the other cloud), it acquires an opposite charge by induction. A spark may occur between the two oppositely charged clouds (or a charged cloud and the earth). This spark is called lightning.

Question 18

Question 19What are the effects of lightning?

Accepted Answer

The effect of lightning on objects is very dangerous and serious. It can kill humans and animals. It can cause a fire and destroy buildings.

Question 19

Question 20What is a lightning conductor? How does it work?

Accepted Answer

A lightning conductor is a device which is used to protect buildings from being damaged due to lightning.The lightning conductor works on the principle of induction.When a charged cloud passes over the tall building, an opposite charge is induced on the spikes of lightning conductor. This charge passes to the earth through the copper rod. Thus, the lightning spark is prevented and the building is protected from being damaged.

Question 20

Question 21How is a tall building protected from damage due to lightning?

Accepted Answer

A lightning conductor is used to protect buildings from being damaged due to lightning. It consists of a long copper rod with sharp points or spikes projecting above the top of the building. The lower end of the rod is connected to a copper plate buried deep into the ground. When a charged cloud passes over the tall building, the spikes of lightning conductor get oppositely charged. This charge passes to the earth through the copper rod. Thus, the lightning spark is prevented and the building is protected from being damaged.

Static Electricity

Exercise 8B Assertion Reason Type

Exercise 8B Long Answer Type Questions

Exercise 8B Short Answer Type Questions

Exercise 8B True Or False