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Charging by induction - class-XII

Description: charging by induction
Number of Questions: 63
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Tags: static electricity electrostatics physics electric charges and fields
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The number of electrons that must be removed from an electrically neutral silver dollar to give it a charge of $+2.4C$ is

  1. $2.5\times { 10 }^{ 19 }$

  2. $1.5\times { 10 }^{ 19 }$

  3. $1.5\times { 10 }^{ -19 }$

  4. $2.5\times { 10 }^{ -19 }$


Correct Option: B
Explanation:

Total charge, $q=+2.4C$
Then by quantization of charge $q=ne$
$\therefore$ number of electrons, $\quad n=\cfrac { q }{ e } =\cfrac { 2.4C }{ 1.6\times { 10 }^{ -19 } } =1.5\times { 10 }^{ 19 }\quad \quad $

Induction is possible

  1. Only in conductor

  2. Only in insulator

  3. Both in conductor and insulator

  4. None of these


Correct Option: C

When a glass rod is rubbed with silk it gains positive charge,because 

  1. Electrons are removed from it

  2. Protons are removed from it

  3. Proton are added to it

  4. Electron are added to it


Correct Option: A

The process due to which an uncharged body acquires electric charges when held near a charged body is called :

  1. conduction

  2. induction

  3. convection

  4. none of these


Correct Option: B
Explanation:

Answer is B.

If a negatively charged object is used to charge a neutral object by induction, then the neutral object will acquire a positive charge. And if a positively charged object is used to charge a neutral object by induction, then the neutral object will acquire a negative charge.
Hence, the process due to which an uncharged body acquires electric charges when held near a charged body is called induction.

When a glass rod is rubbed with silk, the charge acquired by the silk is :

  1. negative

  2. positive

  3. partly positive and partly negative

  4. none of these


Correct Option: A
Explanation:

When a glass rod is rubbed with silk and brought near a GLE, the leaves of the GLE appear to diverge further.
When the glass rod touches the brass of the disc of the GLE, the free electrons from it flow to the glass rod. This causes a deficiency of electrons on the brass disc. To make up for this deficiency the electrons from the fold leaves flow towards the disc. This in turn causes electron deficiency on the gold leaves. As gold leaves as positively charged, they repel each other and hence diverge. Therefore the glass rod has a negative charge.
Hence, the charge acquired by the silk is negative charge.

A glass rod rubbed with silk is brought near the fur rubbed with an ebonite rod. What will be your observation between them?

  1. Attraction

  2. Repulsion

  3. No change

  4. cant say


Correct Option: B
Explanation:

Rubbing the glass rod with the silk makes it lose electrons, so it becomes positively charged.similarly rubbing the fur with the ebonite makes it lose electrons and becomes positively charged.
Since, both glass rod and fur are positively charged and like charges repel each other. So, both the glass rod and fur will repel each other.

Charging by friction is accompanied by loss or gain of electrons. State which body loses electrons when an ebonite rod is rubbed with fur.

  1. $ebonite$

  2. $fur$

  3. $hand$

  4. $Both\ fur\ and\ ebonite$


Correct Option: B
Explanation:

On rubbing an ebonite rod with fur or cat's skin, the electrons from the fur gets transferred to the ebonite rod. The fur now has a deficiency of electrons and so is positively-charged. On the other hand, the ebonite rod has an excess of electrons and hence is negatively-charged. In the above example, the fur undergoes positive electrification. It should be noted that it is the electrons and not the protons that get transferred during positive (and negative) electrification.
Therefore, in this case of electric conduction, the fur losses it electrons to the ebonite rod.

Charging by friction is accompanied by loss or gain of electrons. State which body loses electrons when a glass rod is rubbed with silk.

  1. $glass\ rod$

  2. $silk$

  3. $hand$

  4. $both\ glass\ rod\ and\ silk$


Correct Option: A
Explanation:

On rubbing a glass rod with silk, the electrons from the glass rod get transferred to the silk. The silk now has an excess of electrons and so is negatively-charged. On the other hand, the glass rod is deficient in electrons and hence is positively-charged.
In the above example, the silk undergoes negative electrification.
Therefore, in this case of conduction, the glass rod losses it electrons to the silk.

Which of the following statement is NOT true?

  1. lightning and spark from wollen clothing are essentially the same phenomena.

  2. when you rub a plastic scale on your dry hair, it acquires a charge.

  3. charge acquired by a glass rod when it is rubbed with silk is called as negative charge

  4. static charges are called so, because they donot move by themselves


Correct Option: C
Explanation:

The charge acquired by the glass rod when it is rubbed with silk is positive since electrons get transferred from glass rod to silk.  

If a body acquires electric charge temporarily under the influence of charged body, then the process is called:

  1. conduction

  2. induction

  3. radiation

  4. dispersion


Correct Option: B
Explanation:

Induction. 
Induction is the process by which an electrical effect id produced by an electrical conductor when it is exposed to the the influence of field of force.

The process of charging a conductor from a charged body without touching them together is called induction

  1. True

  2. False

  3. Ambiguous

  4. Data insufficient


Correct Option: A
Explanation:

Answer is A.

Electrostatic induction is a redistribution of electrical charge in an object, caused by the influence of nearby charges. In the presence of a charged body, an insulated conductor develops a positive charge on one end and a negative charge on the other end.
Hence, the statement is true. 

What happens when two straws are individually rubbed with separate sheets of paper and are brought near to each other?

  1. The straws attract each other

  2. The straws repel each other

  3. The straws remain indifferent of each other

  4. Either A or B


Correct Option: B
Explanation:

It is because both the object are rubbed with a sheet of paper and they acquires same charges so they repels each other. 

What happens when a charged balloon is placed near another balloon of the same charge?

  1. Attract each other

  2. Repel each other

  3. Neither attract nor repel

  4. All of the above


Correct Option: B
Explanation:

Both the balloons are charged and having same charge,  therefore they will repel each other. 

When the ebonite rod is rubbed with fur, the charge acquired by the fur is:

  1. negative

  2. positive

  3. both positive and negative

  4. none of these


Correct Option: B

Electrostatic induction is used to charge

  1. Conductors

  2. Semiconductors

  3. Insulators

  4. All of the above


Correct Option: A
Explanation:
The presence of electric charges on the insulator and the electric charges on the insulator and the electric forces they apply to the conduction electrons - creates or induces, the dipole in the conductor. This produces electrostatic charge on conductors.

Two bodies are changed by rubbing one against the other. During the process, one becomes positively charged while the other becomes negatively charged. Then,

  1. mass of each body remains unchanged.

  2. mass of each body changes marginally.

  3. mass of each body changes slightly and hence the total mass.

  4. mass of each body changes slightly but the total mass remains the same.


Correct Option: D
Explanation:
The transfer of electrons from one body to the result in redistribution of charges.
Hence, no. of electrons given by one body $=$ Number of electrons obtained by the other.
$\therefore$ Mass of negatively charged body slightly increases.
Whereas the total mass of the system remain the same.

Which of the following statement is NOT true?

  1. Lightning and spark from woolen clothing are essentially the same phenomena.

  2. When you rub a plastic scale on your dry hair, it acquires a charge.

  3. Charge acquired by a glass rod when it is rubbed with silk is negative charge.

  4. Static charges are called so, because they do not move by themselves.


Correct Option: C
Explanation:

Benjamin Franklin showed for the first time that lightning and spark from our clothes are essentially the same phenomena.

When a plastic scale is rubbed with dry hair, it acquires a small charge. These objects are called charged objects. In the process of charging the plastic scale hair also get charged.
When you are rubbing the glass rod with the silk cloth, electrons are stripped away from the atoms in the glass and transferred to the silk cloth. This leaves the glass rod with more positive than negative charge, so you get a net positive charge.

A glass rod is rubbed with silk, is found positively charged. This is because.

  1. Electrons are transferred from glass rod to silk.

  2. Electrons are transferred from silk to glass rod.

  3. Protons are transferred from glass rod to silk.

  4. Protons are transferred from silk to glass rod.


Correct Option: A
Explanation:

When you are rubbing the glass rod with silk cloth, electrons are stripped away from the atoms in the glass and transferred to the silk cloth.

Hence, option A is correct.

When a piece of polythene is rubbed with wool, a charge of $-2\times 10^{-7}C$ is developed on polythene. What is the amount of mass, which is transfered to polythene.

  1. $11.48\times 10^{19}kg$

  2. $11.58\times 10^{-19}kg$

  3. $11.68\times 10^{-19}kg$

  4. $11.38\times 10^{-19}kg$


Correct Option: C

What causes electrification of two bodies when they are rubbed together ?

  1. Transfer of atoms from one body to the other body.

  2. Transfer of electricity from one body to the other body.

  3. Transfer of electrons from one body to the other body.

  4. Transfer of heat from one body to the other body.


Correct Option: C
Explanation:

Electrification is defined as the transfer of electrons from one body to another when they are rubbed with each other.

Negative electrification is due to the excess of electrons (compared to the normal number of electrons in a neutral atom).
For example, on rubbing a glass rod with silk, the electrons from the glass rod get transferred to the silk. The silk now has an excess of electrons and so is negatively-charged. On the other hand, the glass rod is deficient in electrons and hence is positively-charged.
In the above example, the silk undergoes negative electrification.

Positive electrification is due to the deficiency of electrons (compared to the normal number of electrons in a neutral atom).
For example, on rubbing an ebonite rod with fur or cat's skin, the electrons from the cat's skin get transferred to the ebonite rod. The cat's skin now has a deficiency of electrons and so is positively-charged. On the other hand, the ebonite rod has an excess of electrons and hence is negatively-charged. In the above example, the cat's skin undergoes positive electrification. It should be noted that it is the electrons and not the protons that get transferred during positive (and negative) electrification.

A neutral rubber rod and a neutral piece of fur have equal amounts of negative and positive charge. When the fur is rubbed against the rod, a transfer of electrons occurs. The transfer of electrons and mass transfer respectively takes place from

  1. fur to rubber rod; rubber rod to fur

  2. fur to rubber rod; fur to rubber rod

  3. rubber rod to fur; rubber rod to fur

  4. rubber rod to fur; fur to rubber rod


Correct Option: B
Explanation:

Answer is B.

On rubbing an rubber rod with fur, the electrons from the fur get transferred to the rubber rod. The fur now has a deficiency of electrons and so is positively-charged. On the other hand, the rubber rod has an excess of electrons and hence is negatively-charged.
In the above example, the fur undergoes positive electrification. It is to be noted that it is the electrons and not the protons that get transferred during positive (and negative) electrification.
Here, the transfer of electrons and mass transfer respectively takes place from fur to the rubber rod.

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


Correct Option: B
Explanation:

Answer is B.

Negative electrification is due to the excess of electrons (compared to the normal number of electrons in a neutral atom).For example, on rubbing a glass rod with silk, the electrons from the glass rod get transferred to the silk. The silk now has an excess of electrons and so is negatively-charged. On the other hand, the glass rod is deficient in electrons and hence is positively-charged.
In the above example, the silk undergoes negative electrification.
Hence, the glass rod 
becomes positively charged while the silk cloth has a negative charge.

When a glass rod is rubbed with silk

  1. Negative charge is produced on silk but not charge on the glass rod

  2. Equal but opposite charge are produced on the both

  3. Equal and similar charges are produced on the both

  4. Positive charge is produced on the glass rod but no charge on the silk


Correct Option: B
Explanation:

When glass rod is rubbed with silk, 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.

Thus equal but opposite charge are produced on the both.
Hence, option B is correct.

A hollow metallic sphere is charged. Inside the sphere

  1. The potential is zero but the electric field is finite

  2. The electric field is zero but the potential is finite

  3. Both the electric field and the potential are finite

  4. Both the electric field and the potential are zero


Correct Option: B

When a glass rod is rubbed with silk, it is said to be positively charged. Which of the following statement is true?

  1. Electrons move from silk to glass

  2. Electrons move from glass to silk

  3. Protons move from silk to glass

  4. Protons move from glass to silk


Correct Option: B
Explanation:

When a glass rod is rubbed with silk, it acquires a positive charge, means it is deficit of electrons i.e, electrons move from glass to silk. So glass rod becomes positively charged and silk rod is negatively charged.

Two uncharged bodies when rubbed against each other get charged. This is known as

  1. Charging by conduction

  2. Charging by friction

  3. Charging by induction

  4. Charging by convection


Correct Option: B
Explanation:

Charging by friction refers to generation of charge on uncharged bodies when rubbed against each other. One of the rubbed material loses electrons and becomes positively charged and other material gains that electron and becomes negatively charged.

When a plastic comb rubbed on hair is brought near bits of paper, it attracts them because:

  1. The comb and the paper get similarly charged.

  2. They get oppositely charged.

  3. The paper bits are very light.

  4. None of these


Correct Option: B
Explanation:

A comb rubbed on hair gets electrically charged. It attracts small bits of paper because opposite charges attract. So, comb and bits of paper are oppositely charged.

If a body is charged by rubbing it, its weight _________.

  1. Remains precisely constant

  2. Increases slightly

  3. Decreases slightly

  4. May increase or decrease slightly


Correct Option: D
Explanation:

If a body is charged by rubbing it, then it may lose or gain electrons. Since electrons have a mass of $(9.1\times 10^{-31} :Kg)$. So, a slight weight may increase or decrease slightly.

The process suitable for charging a glass rod is :

  1. conduction

  2. induction

  3. rubbing against a suitable substance

  4. all of the above


Correct Option: C
Explanation:

The process suitable for  charging a glass rod is by friction,means by rubbing against a suitable substance.


Option C is correct.

During electrification by friction

  1. Proton are transferred from one body to another body

  2. Neutrons are transferred from one body to another body

  3. Electrons are transferred from one body to another body

  4. None


Correct Option: C
Explanation:

When a body is rubbed over another,transfer of electrons from one body to another. Thus one body acquires a net positive charge and the other acquires net negative charge.proton and neutron are packed in the nucleus thus they cannot move.

example - When a glass rod is rubbed with a silk cloth some electrons from the glass attach themselves to the silk. Consequently, the glass becomes positively charged and the silk negatively charged. Likewise when ebonite is rubbed with fur electrons are transferred from fur to ebonite, thus making the ebonite negative and the fur positive.

Option C is correct.

An ebonite rod rubbed with fur and a glass rod rubbed with silk cloth are brought nearer to each other. Then

  1. they will attract each other

  2. they will repel each other

  3. nothing will happen to them

  4. they will get heated up


Correct Option: A
Explanation:

When an ebonite rod is rubbed with fur, the ebonite rod gets negatively charged and the fur becomes positively charged. Whereas when a glass rod is rubbed with silk cloth, the glass rod becomes positively charged and the silk cloth becomes negatively charged.

Now as we know that unlike charges attract each other, thus the glass rod and the ebonite rod will attract each other as they have opposite charges.

Which of the following statement is NOT true?

  1. Lightning and spark from woolen clothing are essentially the same phenomena.

  2. When you rub a plastic scale on your dry hair, it acquires a charge.

  3. Charge acquired by a glass rod when it is rubbed with silk is called as negative charge.

  4. Static charges are called so, because they do not move by themselves


Correct Option: C
Explanation:

When a glass rod is rubbed with silk then it gets net positive charge whereas silk gets negatively charges by electron transfer through friction.When a glass rod is rubbed with silk, it acquires a positive charge whereas silk acquires a negative charge. So, statement is not True.

The electric charge developed on glass rod rubbed with silk cloth is different from the charge developed on ebonite rod rubbed with fur.

  1. True

  2. False


Correct Option: A
Explanation:

When glass rod is rubbed with silk cloth, it acquires positive charge.
But when ebonite rod is rubbed with fur, the rod gets negatively charged.
So, charge developed on glass rod rubbed with silk is different from charge developed on ebonite rod rubbed with fur. Hence this statement is true.

The electricity developed on objects, when they are rubbed with each other is called:

  1. Frictional potential

  2. Frictional electricity

  3. Static electricity

  4. Static potential


Correct Option: B
Explanation:

The electricity developed on the objects when they are rubbed with each other is called Frictional electricity. On rubbing two objects, both materials get electrified due to friction produced while rubbing them. One of the body acquires negative charge and other acquires positive charge.

A woolen cloth when rubbed against plastic object acquires ______ charge.

  1. Sometimes positive and sometimes negative

  2. Negative

  3. Positive

  4. None of the these


Correct Option: C
Explanation:

When woolen cloth is rubbed against the plastic, both wood and plastic get electrified due to friction produced while rubbing. So, plastic has greater electron affinity (ability to attract electrons) as compared to wool, therefore, plastic acquires negative charge and wool acquires positive charge.

A glass rod when rubbed with silk cloth, acquires a charge of $1.6\times 10^{-11}C$, then the charge on silk cloth will be:

  1. $-3.2\times 10^{-11}C$

  2. $-2.4\times 10^{-13}C$

  3. $-1.6\times 10^{-13}C$

  4. $-1.6\times 10^{-11}C$


Correct Option: D
Explanation:

When glass rod is rubbed with silk, electrons move from rod to silk.


Since silk gets electrons it becomes negatively charged and the number of electrons gained by silk is same as that lost by rod.

Hence magnitude of charge on silk is same as that on rod.

Hence charge on silk$=-1.6\times 10^{-11}C$ 

Answer-(D)

When a polythene piece is rubbed with wool, it acquires negative charge. 

  1. True

  2. False


Correct Option: A
Explanation:

When a polythene piece is rubbed with wool, both gets electrified due to charging by friction. Since polythene has greater electron affinity (ability to attract electrons) as compared to wool. So, polythene piece attracts electron and acquires negative charge and wool acquires positive charge.

Which statement best explains why a rubber rod becomes negatively charged when rubbed with fur?

  1. The rubber that the rod is made of is a better insulator than fur.

  2. The fur is a better insulator than the rubber.

  3. Molecules in the rubber rod have a stronger attraction for electrons than the molecules in the fur.

  4. Molecules in the fur have a stronger attraction for electrons than the molecules in the rubber rod.


Correct Option: C
Explanation:

During charging by rubbing (or by friction) process, the material that becomes negatively charged does so because it likes electrons more than the material with which it is rubbed. It means molecules in rubber rod have a stronger attraction for electrons than the molecules in the fur. 

During a physics lab, a plastic strip was rubbed with cotton and became positively charged. The correct explanation for why the plastic strip becomes positively charged is that

  1. the plastic strip acquired extra protons from the cotton.

  2. the plastic strip acquired extra protons during the charging process.

  3. protons were created as the result of the charging process.

  4. the plastic strip lost electrons to the cotton during the charging process.


Correct Option: D
Explanation:

Plastic strip when rubbed with cotton got charged due to charging by friction.
The plastic strip and cotton acquires opposite charges. This is because plastic strip acquires positive charges and loses electrons to cotton during the process, and therefore cotton acquires the negative charge.

During charging by friction, 

  1. charge is created.

  2. charged is destroyed.

  3. charge is conserved.

  4. None of these


Correct Option: C
Explanation:

When two objects rub each other, then due to friction, one object's electrons gets transfered to the other one.

The one which loses electrons becomes positively charged and the other, negative.
Thus charging by friction is only due to transfer of electrons. No charge gets created or destroyed in this process.

Charging by friction is used to develop charges on 

  1. metals

  2. conductors

  3. insulators

  4. Non of these


Correct Option: C
Explanation:

Insulators are the materials that do not allow electrons to flow through them easily. Therefore, insulators can be easily charged by friction as the extra electrons gained cannot escape easily. 

Which property of a material is paramount to it being charged by friction?

  1. electron affinity

  2. electronegativity

  3. potential difference

  4. None of these


Correct Option: A
Explanation:

Electron affinity refers to the relative amount of love that a material has for electrons. If atoms of a material have high electron affinity, then that material will have relatively higher love for electrons. This property of electron affinity will be of utmost importance as we consider the common method of charging i.e, charging by friction or rubbing.

A redistribution of electrical charge in an object, caused by the influence of nearby charges is termed as

  1. electric conduction

  2. ionisation

  3. electrostatic induction

  4. electromagnetic induction


Correct Option: C
Explanation:

According to the definition of electrostatic induction, it is a redistribution of electrical charge in an object, caused by influence of nearby charges. In the presence of a charged body, an insulated conductor develops a positive charge on one end and a negative charge on other end. Such charges are called induced charges and the process is called electrostatic induction. 

If the object is not grounded while performing electrostatic induction, the nearby charge will 

  1. induce equal and opposite charges in the object.

  2. induce equal charges in the object.

  3. induce opposite charges in the object.

  4. None of the above


Correct Option: A
Explanation:

It is one of the rule of charging by induction, that if the object is not grounded, the nearby charge will induce equal and opposite charges in the object. 

Induced charge resides at/in the

  1. bulk of the object

  2. centre of the object

  3. surface of the object

  4. All of the above


Correct Option: C
Explanation:

Whenever an induced charge is produced in an object, the charge spreads uniformly and distribute itself on its surface. 

An application of electrostatic induction is

  1. electric generator

  2. Van de Graff generator

  3. Wimhurst machine

  4. transformer


Correct Option: B,C
Explanation:

Electrostatic induction is a redistribution of electrical charges in an object caused by the influence of nearby charges. Electrostatic generators such as the Wimshurst machine, the Vande Graph generator use this principle. 

Paper snippets attracted by a charged CD is an example of

  1. charging by induction

  2. charging by conduction

  3. charging by ionisation

  4. charging by transmission


Correct Option: A
Explanation:

When a charged $CD$ is brought near the paper snippets, opposite charge is induced on the paper snippets. As opposite charges attract, paper snippets are attracted by charged $CD$. So, this is an example of charging by induction. 

In charging by conduction, the charged object 

  1. ends up oppositely charged to the object used to charge it.

  2. ends up similarly charged to the object used to charge it.

  3. discharges the object used to charge it, completely.

  4. discharges the object used to charge it, to some extent.


Correct Option: B
Explanation:

In case of charging by conduction, when an uncharged conductor is touched with a charged conductor, the uncharged conductor acquires charge similar to charged conductor. It happens because of the electrons are shared at the point of contact of the conductors. 

Charging by friction can be explained by

  1. electrostatic conduction

  2. electrostatic induction

  3. ionisation

  4. All of the above


Correct Option: A
Explanation:

In both the methods, i.e, charging by friction and electrostatic conduction, the two bodies are brought in contact and sharing of electrons occurs at the point of contact. So, charging by friction can be explained by electrostatic conduction. 

Rub a piece of ebonite across a piece of animal fur. What happens?

  1. the fur has a slightly positive charge and the ebonite is slightly negative

  2. the fur has a slightly positive charge and the ebonite is also slightly positive

  3. the fur has a slightly negative charge and the ebonite is also slightly negative

  4. the fur has a slightly negative charge and the ebonite is slightly positive


Correct Option: A
Explanation:

When a piece of ebonite is rubbed with a piece of animal fur, frictional charging process results in a transfer of electrons between the two objects. Since ebonite has much greater attraction for electrons than animal fur (electron affinity). As a result, atoms of ebonite pull electrons from atoms of animal fur, and as a result, ebonite becomes negatively charged  and animal fur becomes positively charged. 

An imbalance of electric charges within or on the surface of a material is 

  1. current electricity

  2. an electromagnetic wave

  3. static electricity

  4. None of these


Correct Option: C
Explanation:

Static electricity is an imbalance of electric charges within or on the surface of a material. The charge remains until it is able to move away by means of an electric current or electrical discharge. So, this is the definition of static electricity. 

Rub a glass rod with a piece of silk. What happens?

  1. the glass has a slightly positive charge and the silk is also slightly positive

  2. the glass has a slightly positive charge and the silk is slightly negative

  3. the glass has a slightly negative charge and the silk is also slightly negative

  4. the glass has a slightly negative charge and the silk is slightly positive


Correct Option: B
Explanation:

When a glass rod is rubbed with silk, both gets electrified due to charging by function by rubbing. One of the body acquires negative charge and other positive charge due to shifting of electrons from one body to other. Since silk has greater electron affinity (ability to attract electrons) as compared to glass. So, silk acquires slight negative charge and glass acquires slight positive charge.

A balloon gets negatively charged by rubbing ceilings of a wall.

  1. This implies that the wall is positively charged.

  2. This implies that the wall is negatively charged.

  3. This does not imply that the wall is positively charged.

  4. None of these


Correct Option: C
Explanation:

A balloon gets negatively charged by rubbing ceilings of wall. But this does not imply that the wall is positively charged. The balloon induces a charge of opposite sign in the ceilings of the wall, causing the ceiling and the balloon to be attracted to each other. The balloon eventually falls because its charge slowly diminishes as it leaks to ground. Some of the charge on the balloon could also be lost due to the presence of positive ions in the surrounding atmosphere, which would tend to neutralize the negative charges on the balloon.

A comb run through ones hair attracts small bits of paper. What happens, if the hair are wet or if it is a rainy day? 

  1. The comb does not get charged and it will not attract small bits of paper.

  2. The comb does not get charged but it will attract small bits of paper.

  3. The comb does gets charged and it will attract small bits of paper.

  4. The comb does gets charged but it will not attract small bits of paper.


Correct Option: A
Explanation:

Comb gets electrically charged by friction when even through dry hair. It attracts small bits of paper because paper gets polarized in the presence if charged comb resulting in a net force of attraction. When hair is wet, the friction between comb and hair decreases and comb does not get charged. Hence, it may not attract small bits of paper.

A balloon gets negatively charged by rubbing ceilings of a wall. 

  1. The balloon sticks to the ceiling forever.

  2. The balloon eventually fall off the ceiling.

  3. The balloon does not stick to the ceiling at all.

  4. The balloon charges the ceiling negatively.


Correct Option: B
Explanation:

The balloon is negatively charged on rubbing with the wall means that on rubbing, the balloon collects electrons from the wall and making it negative in respect to the wall and therefore it clings to the wall, while clinging to the wall, the electrons on the balloon leaks off the balloon and eventually leaves. The balloon at the same potential as the wall, thus when the attraction between the balloon and wall is less than the weight of the balloon, the balloon eventually falls off. 

Which of the following charging methods work without ever touching the object to be charged to the object used to charge it?

  1. charging by friction

  2. charging by contact

  3. charging by induction

  4. all of these


Correct Option: C
Explanation:

When a charge $Q$ is brought near (but not touching) an uncharged conductor, the charge $Q$ induces a charge of opposite polarity on the facing surface of the conductor and the same polarity on the rearer surface. This process of inducing a charge on the conductor without touching is known as charging induction.

Whereas charging by friction and contact work only when the surface of the two object are in contact with each other.

State whether the given statement is True or False :

When silk is rubbed with glass, the silk gets positively charged.

  1. True

  2. False


Correct Option: B
Explanation:

When silk is rubbed with glass, 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. 

When a body is charged by induction, then the body

  1. Becomes neutral

  2. Does not lose any charge

  3. Loses whole of the charge on it

  4. Loses part of the charge on it


Correct Option: B
Explanation:

The part of the body nearer to the source charge gets induced charges, opposite in nature to the source charge while the other part gets those of similar nature.Thus no loss of charge.

A polythene piece rubbed with wool is found to have a negative charge of $3.6\times 10^{-7}C.$ Calculate the number of electrons transferred from wool to polythene:

  1. $6.25\times 10^{18}$

  2. $2.25\times 10^{12}$

  3. $2.05\times 10^{-18}$

  4. $2.18\times 10^{10}$


Correct Option: B
Explanation:

$n=\dfrac {q}{e}=\dfrac {-3.6\times 10^{-7}C}{-1.6\times 10^{-19}C}$

$=2.25\times 10^{12}$
$\therefore 2.25\times 10^{12}$ electrons are transferred from wool to polythene.

In induction the charge induced in the near surface of a dielectric is:

  1. equal and similar

  2. greater and dissimilar

  3. lesser and dissimilar

  4. equal and dissimilar


Correct Option: C
Explanation:

In induction, the charge induced in the near surface of a dielectric is lesser and dissimilar.

A sure test of electrification is:

  1. attraction

  2. repulsion

  3. friction

  4. induction


Correct Option: B
Explanation:

Repulsion is the sure test of electrification.
Note: If two bodies are electrified (i.e., charged they can either attract or repel). If they are:
(a) attracted: this is not only possible by electrification but can also be due to the attraction of an uncharged body with charged body.
(b) repulsion: repulsion is possible only when both objects are charged oppositely.

When a glass rod is rubbed with silk, both become charged due to:

  1. migration of protons

  2. exchange of electrons and protons

  3. migration of electrons

  4. migration of neutrons


Correct Option: C
Explanation:

When a glass rod is rubbed with silk cloth glass rod becomes positively charges while silk cloth becomes negatively charged. This is due to transfer or migration of electrons from glass rod to silk cloth.

A glass rod when rubbed with silk cloth acquires a charge $1.6 \times 10^{-13}  C$. What is the charge on the silk cloth?

  1. $-1.6 \times 10^{-19} C$

  2. $1.6 \times 10^{-13} C$

  3. $-1.6 \times 10^{-13} C$

  4. $1.6 \times 10^{-19} C$


Correct Option: C
Explanation:

When a glass rod is rubbed with silk, both gets electrified due to charging by friction. Given, glass rod acquires positive charge $=1.6\times 10^{-31}\, C$. So silk acquires equal and opposite charge as that on glass rod. Hence the answer is $-1.6\times 10^{-13}\, C$.

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