0

Electric force - class-XII

Attempted 0/63 Correct 0 Score 0

Complete the following sentences:

Like charges ...... , while unlike charges ...... each other.

  1. attract, attract

  2. repel, repel

  3. attract, repel

  4. repel, attract.


Correct Option: D
Explanation:

There are 2 types of electrical charges - positive and negative - are said to be opposite types of charge. Consistent with our fundamental principle of charge interaction, a positively charged object will attract a negatively charged object. Oppositely charged objects will exert an attractive influence upon each other. In contrast to the attractive force between two objects with opposite chargess, two objects that are of like charge will repel each other. That is, a positively charged object will exert a repulsive force upon a second positively charged object. This repulsive force will push the two objects apart. Similarly, a negatively charged object will exert a repulsive force upon a second negatively charged object. Objects with like charge repel each other.
Therefore, Like charges repel, while unlike charges attract each other.

If two bodies A and B (A bigger in size than B) are rubbed together, then :

  1. A and B get equal and opposite charges

  2. A and B get equal and similar charges

  3. A gets more charge than B, but of opposite kind

  4. A gets less charge than B, but of same kind


Correct Option: A
Explanation:

Answer is A.

Static electricity is created when two objects are rubbed together, causing an object to give up or gain electrons. The electric charges that are created do not depend on the size of the objects. Therefore, when two bodies are rubbed together, both the bodies transfer electrons to and fro between the bodies and they obtain equal and opposite charges. The body that gives away electrons, gains positive charge and the body that obtains electrons gains negative charge.

Two uncharged bodies on rubbing, get charged due to:

  1. conduction

  2. friction

  3. induction

  4. none of these


Correct Option: B
Explanation:

Answer is B.

When two bodies are rubbed together, there is transfer of electrons because of friction.
Hence, two uncharged bodies on rubbing, gets equal and opposite charges.

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. Then :

  1. the sphere close to the rod acquires a negative charge and the other sphere acquires a positive charge

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

  3. both the spheres will acquire positive charge

  4. both the spheres will acquire negative charge


Correct Option: C
Explanation:

Since the rod which was brought closer was negatively charged the induced charge acquired by the spheres will be positive. 

An inflated balloon was pressed against a wall after it has been rubbed with a piece of synthetic cloth. It was found that the balloon sticks to the wall. What force might be responsible for the attraction between the balloon and the wall?

  1. Gravitational

  2. Magnetic

  3. Electrostatic

  4. adhesive


Correct Option: C
Explanation:

Electrostatic force is the phenomenon that results from slow-moving or stationary electrical charges. Specifically, electrostatic force is the physical reaction that holds together the electromagnetic field created by subatomic particles, such as electrons and protons. In order for electrostatic forces to remain cohesive, these particles need to independently maintain both positive and negative charges and react to each other accordingly. 
When a balloon is rubbed with a cloth, the electrons from the atoms of the cloth enter the atoms of the balloon and the number of electrons in the atoms of balloon becomes more than the number of protons. Because of that, there is a negative charge in the balloon, and in the cloth the number of electrons in its atoms become less than the number of protons, so it's positively charged.
Therefore, due to this electrostatic force, the balloon sticks to the wall.

Like charges attract each other:

  1. True

  2. False


Correct Option: B
Explanation:

Answer is B.

The statement is false because only unlike poles attract each other. Like poles repel each other.

A soap bubble is given a negative charge, then its radius :

  1. Decrease

  2. Increase

  3. Remains unchanged

  4. Can't say


Correct Option: B
Explanation:

Answer is B.

By symmetry, the charge will distribute evenly over the surface of the bubble. Because like charges repel, they want to move even further apart, the only which way is outward, taking the soap surface with them. Of course, the increase in restoring force of the soap film (surface tension) will at some point be equal and opposite to the electrostatic force, resulting in a new (larger) equilibrium radius.
This will happen to both positive and negatively charged bubbles because of the ionic similarity.
Hence, when the soap bubble is given a negative charge, then its radius will increase.

Electric switches and appliances should be tested only with 

  1. Right hand

  2. Left hand

  3. Both hands

  4. Electric tester


Correct Option: D
Explanation:

We should not touch the electric appliance with bare hands. To check the supply in the circuit, the electric tester should be used.

Lightning is a ________ phenomenon

  1. Electromagnetic

  2. Current electricity

  3. Electrochemical

  4. Electrostatic


Correct Option: D
Explanation:

Lightning is a sudden electrostatic discharge during an electrical storm between electrically charged regions of a cloud, between that cloud and another cloud, or between a cloud and the ground.

Sometimes you get a mild spark when you touch the metal surface of a car. What might be the reason?

  1. Due to magnetic attraction, a spark is created

  2. Due to electrostatic charge residing on the metal as well as on skin, mild spark is observed

  3. Car tries to become neutral by donating electrons

  4. Its the only path to ground


Correct Option: B
Explanation:

Negative electric charge often resides on the surface of metal of car. When you touch the car, electrostatic discharge occurs via your body and you get a mild spark.

Which is not an electrostatic phenomenon

  1. Comb rubbed with hair attracts paper bits

  2. A blanket in winters in dark when scrambled gives electrical sparks

  3. Two people shaking hands feel a small spark in winters

  4. Heat is generated in a resistor carrying current


Correct Option: D
Explanation:

(d) is based on Joule's Law.

Rest are electrostatic phenomenon.

.......... Property develops in comb due to friction.

  1. Attractive

  2. Repulsive

  3. Both

  4. None


Correct Option: A
Explanation:

An attractive property is develop in the comb due to friction. The comb on rubbing over dry hairs is aid to be charged.

......... Charge is produced by friction

  1. Stationary

  2. No

  3. Attractive

  4. All


Correct Option: A
Explanation:

The stationary charge (i.e static electricity) is produced by friction.

If a glass rod is rubbed on silk cloth and then brought near the bits of paper it...... then.

  1. Attracts

  2. Repel

  3. Both

  4. None


Correct Option: A
Explanation:

If a ordinary glass rod is rubbed on the silk cloth is brought near bits of paper, it is found that they have acquired the attractive property. The glass rod get charged on rubbing.

What is known as electrostatic attraction?

  1. When negatively charged atom is attracted towards positively charged atom

  2. When positively charged atom is attracted towards negatively charged atom

  3. When positively charged atom is attracted towards positively charged atom

  4. When negatively charged atom is attracted towards negatively charged atom


Correct Option: A
Explanation:

When negatively charged atom is attracted towards positively charged atom, it is known as electrostatic attraction.


Option A is correct.

What is known as electrostatic repulsion?

  1. When two positively or two negatively charged electrons come closer to each other then they repel from each other

  2. When two charged electrons come closer to each other then they repel from each other

  3. When positively and negatively charged electrons come closer to each other then they repel from each other

  4. None


Correct Option: A
Explanation:

When two positively or two negatively charged electrons come closer to each other then they repel from each other. Then it is known as electrostatic repulsion.


Option A is correct.

The law that describes the force as directly proportional to magnitude of charges and inversely proportional to the distance between the charges is known as :

  1. Newton's law

  2. Coulomb's law

  3. Gauss's law

  4. Ohm's law


Correct Option: B
Explanation:

Newton's law : force $F=ma$  where m=mass and a=acceleration

Coulomb's law : force $F=\dfrac{kq _1q _2}{r^2}$ where $q _1, q _2 $ are charges and $r=$ separation of charges and $k=$ proportionality constant.
Gauss's law : the electric flux $\phi=\dfrac{q}{\epsilon _0}$ 
Ohm's law : Potential across a wire of resistance R is $V=IR$ where I is the current. 

On which factors from below does Coulomb's law(i.e. law of electrostatic attraction and repulsion) depends?

  1. Magnitude of charges

  2. Distance between charges

  3. Both magnitude and distance between charges

  4. None of the above


Correct Option: C
Explanation:

Coulomb's Law : $\dfrac{kq _1q _2}{r^2}$
It depends on both magnitude of charges and distance between them. 

Electric charges which are under the action of electric forces are known as :

  1. Electrostatic

  2. Electric flux

  3. Electric field

  4. Electric field lines


Correct Option: A
Explanation:

Electrostatic : when the charges are under action of electric forces. 

Electric flux : It is the measure of filed lines through a given area. 
Electric field  : the electric force per unit charge. 
Electric field lines : it measure the nature of charges, field lines is outward form positive charges and inner-ward for negative charges.

What does coulomb's law of attraction and repulsion states?

  1. F is directly proportional to $q _1q _2$ and inversely proportional to $(r _{12})^2$

  2. F is directly proportional to $q _1q _2$ and inversely proportional to $(r _{12})$

  3. F is indirectly proportional to $q _1q _2$ and directly proportional to $(r _{12})^2$

  4. None


Correct Option: A
Explanation:

The Coulomb law is the force between two charges $q _1$ and $q _2$ when the separation between them is $r _{12}$. 

Here , $F=\dfrac{kq _1q _2}{r _{12}^2}$
Thus, F is proportional to $q _1q _2$ and invewrsely proportional to $r _{12}^2$.

Which of the following represents Coulomb's constant?

  1. $k\,=\,\frac{1}{4\times \pi \times e^0}$

  2. $k\,=\,1$ + ($4\times \pi \times e^0$)

  3. $k\,=\,1$ - ($4\times \pi \times e^0$)

  4. $k\,=\,1$ * ($4\times \pi \times e^0$)


Correct Option: A
Explanation:

We know that Coulomb's force, $F=\frac{1}{4\pi \epsilon _0} \frac{q _1q _2}{r^2}$


The Coulomb constant will be  $k=\frac{1}{4\pi\epsilon _0}$

The value of the constant $k$ in coulomb's law is :

  1. $9\times10^3$

  2. $9\times10^5$

  3. $9\times10^7$

  4. $9\times10^9$


Correct Option: D
Explanation:

The Coulomb's constant, $k=\dfrac{1}{4\pi\epsilon _0}=\dfrac{1}{4\pi\times (8.85\times 10^{-12})}=9\times 10^9$

When we wear nylon dresses during winter then there is ______ current which gets produced due to contact with out body. Fill in the Blank.

  1. Magnetic

  2. Electrostatic

  3. Potential

  4. kinetic


Correct Option: B
Explanation:

When we wear nylon dresses during winter then there is electrostatic current which gets produced due to contact with out body.


Option B is correct.

When we rub our comb with hair and then take near to the paper pieces, all pieces get stuck to the comb. This happens due tyo which phenomena?

  1. Electrostatic Induction

  2. Magnetic effect

  3. Potential effect

  4. Kinetic effect


Correct Option: A
Explanation:

When negative charges is created in the comb by rubbing it with hair and pieces of paper are exposed to the electric field created by the charge, the part of paper closer to the comb will be positively charged due to electromagnetic induction, and the farther would be negatively charged, causing the paper to be attracted to the comb.

The force between two bodies having charges $5C$ and $10C$ separated by distance of $0.5 m$ in air is :

  1. $18\times 10^{11}\ N$

  2. $9\times 10^{11}\ N$

  3. $9\times 10^{9}\ N$

  4. $18\times 10^{9}\ N$


Correct Option: A
Explanation:

By Coulomb's law, the force between two charges is $F=k \dfrac{q _1q _2}{r^2}=(9\times 10^9)\times \dfrac{5\times 10}{(0.5)^2}=18\times 10^{11} N$

A closed switch has a resistance of :

  1. zero ohm

  2. about $50$ ohms

  3. about $500$ ohms

  4. infinity


Correct Option: A
Explanation:

A closed switch has a Zero resistance.


Option A is correct.

Which of the following materials has a negative temperature coefficient of resistance?

  1. Copper

  2. Aluminium

  3. Carbon

  4. brass


Correct Option: C
Explanation:

Carbon has a negative temperature coefficient of resistance. 

Option C is correct.

An electric filament bulb can be worked from

  1. DC supply only

  2. AC supply only

  3. Battery supply only

  4. All above


Correct Option: D
Explanation:

An electric filament bulb can be worked from

1. AC Current.
2. DC Current.
3. Battery current.

Option D is correct.

The filament of an electric bulb is made of :

  1. Carbon

  2. Aluminium

  3. Tungsten

  4. Nickel


Correct Option: C
Explanation:

The filament of an electric bulb is made of tungsten because it has some amazing properties including the highest melting point $(3422^oC )$, lowest vapor pressure, and greatest tensile strength out of all the metals. Because of these It can reach high temperature before melting.  

Which is the best conductor of electricity?

  1. Iron

  2. Silver

  3. Copper

  4. Carbon


Correct Option: B
Explanation:

Silver is a best conductor of electricity because it contains maximum number of free electron.Also the resistance of silver is very low.


Option B is correct.

True Or False?
1)A proton repels an electron.
2)An electron repels a proton.

  1. False, False

  2. True, True

  3. True, False

  4. False, True.


Correct Option: A
Explanation:

The above statement is false. Unlike charges attract each other. A proton attracts an electron.

Like charges .......... and unlike charges.................

  1. Repel, Attract

  2. Attract, Repel

  3. Always attract

  4. Always repel


Correct Option: A
Explanation:

There are two types of charges, positive and negative. Same type of charges (two positive or two negative) repel each other, while unlike charges (one positive and one negative) attract each other.

Like charges ____________  each other and unlike charges ____________ each other :

  1. repel, attract

  2. attract, repel

  3. repel, repel

  4. attract, attract


Correct Option: A
Explanation:

The like charges repel and unlike charges attract each other, hence option A is correct answer.

An insulated conductor initially free from charge is charged by repeated contacts with a plate which after each contact is replenished to a charge $Q$ from an electrophorus. If $q$ is the charge on the conductor after the first operation,  The maximum charge which can be given to the conductor in this way is $Qq/(Q - q)$.

  1. True

  2. False


Correct Option: A

 A point charge Q is placed at origin O. Let $\overrightarrow {{E _A}} $,$\overrightarrow {{E _B}} $ and $\overrightarrow {{E _C}} $ represent electric fields at A, B and C respectively. If coordination of A,B and C are respectively (1,2,3) m,(1,1,-1) m and (2,2,2) m  then 

  1. $\overrightarrow {{E _A}} \bot \overrightarrow {{E _B}} $

  2. $\overrightarrow {{E _A}} \parallel \overrightarrow {{E _B}} $

  3. $\left| {\overrightarrow {{E _B}} } \right|\parallel 4\left| {\overrightarrow {{E _C}} } \right|$

  4. $\left| {\overrightarrow {{E _B}} } \right|\parallel 8\left| {\overrightarrow {{E _C}} } \right|$


Correct Option: C
Explanation:

$\overrightarrow{E _a}=\cfrac{h _E}{ra^3}=\cfrac{h _E}{1^2+2^2+3^2}(1\hat{i}+2\hat{j}+3\hat{k})\ \overrightarrow{E _a}=\cfrac{h _E}{14^{3/2}}(1\hat{i}+2\hat{j}+3\hat{k})\ \overrightarrow{E _b}=\cfrac{ha}{r _b^2}\overrightarrow{r _b}=\cfrac{h _E}{(1^2+1^2+1^2)}^{3/2}(1\hat{i}-1\hat{j}+1\hat{k})\=\cfrac{h _E}{3^{3/2}}(1\hat{i}-1\hat{j}+1\hat{k})\ \overrightarrow{E _c}=\cfrac{h _E}{r _c^2}\overrightarrow{r _c}=\cfrac{h _E}{(2^2+2^2+2^2)^{3/2}}(2\hat{i}+2\hat{j}+2\hat{k})$

$\quad=\cfrac{h _E}{12^{3/2}}(2\hat{i}+2\hat{j}+2\hat{k})$
Now 
$\overrightarrow{E _a}.\overrightarrow{E _b}=\cfrac{h _E}{14^{3/2}}(1\hat{i}+2\hat{j}+3\hat{k})=\cfrac{h _E}{3^{3/2}}(1\hat{i}-1\hat{j}+1\hat{k})\ \Rightarrow \overrightarrow{E _a}.\overrightarrow{E _b}=(\cfrac{h _E}{14^{3/2}})(\cfrac{h _E}{3^{3/2}})(1-2+3)\neq0$
Thus$\overrightarrow{E _a}$ and $\overrightarrow{E _b}$ are perpendicular to each other
$|E _c|=\cfrac{h _E}{12^{3/2}}(2^2+2^2+2^2)^{1/2}=\cfrac{h _E}{12^{3/2}}(12)^{1/2}\ \Rightarrow |\overrightarrow{E _c}|=\cfrac{h _E}{12}\ \overrightarrow|E _b|=\cfrac{ha}{3^{3/2}}(1^2+1^2+1^2)^{1/2}=\cfrac{ _E}{3}=4\times\cfrac{h _E}{12}=4|\overrightarrow{E _c}|$
So, $|\overrightarrow{E _b}|=4|E _c|$



Objects with the same type of charges attract each other.

  1. True

  2. False


Correct Option: B
Explanation:

Object with same nature of charges repel each other i.e, positive charges repel positive charge and negative charges repel negative charge.

   And charges with opposite nature attract each other that is negative and positive charge attract each other.

Given statement is $False$.

To construct an air filled capacitor which can store $ 12 \mu C $ of charge, What can be the minimum plate area of the capacitor? (Dielectric strength of air is $3\times 10^6 V/m$ )

  1. $0.25 m^2$

  2. $0.45 m^2$

  3. $4.5 m^2$

  4. $0.35 m^2$


Correct Option: C

A conducting sphere of radius a has charge Q on it. It is enclosed by a neutral conducting concentric concentric spherical shell having inner radius 2a and outer radius 5a. Find electrostatic energy of system.

  1. $\dfrac{5}{12} \dfrac{kQ^2}{a}$

  2. $\dfrac{11}{12} \dfrac{kQ^2}{a}$

  3. $]dfrac{kQ^2}{2a}$

  4. $none$


Correct Option: D

A capacitor is a perfect insulator for:

  1. constant direct current

  2. alternating current

  3. direct as well as alternating current

  4. variable direct current.


Correct Option: C

Four charges $+Q,-Q,+Q$ and $-Q$ are situated at the corners of a square; in a sequence then at the centre of the square:

  1. $E=0,V=0$

  2. $E=0,V\neq 0$

  3. $E\neq 0,V=0$

  4. $E\neq 0,V\neq 0$


Correct Option: C
Explanation:

Four charges $+Q$, $-Q$, $+Q$, $-Q$.

In this context, $E\neq 0$ but $V=0$ because. $E$ is not cancel out to each other but $V$ is cancel out each other.

There are two charges $+2\mu\ C\ and -3\mu\ C$. The ratio of forces acting on them will be 

  1. $2:3$

  2. $1:1$

  3. $3:2$

  4. $4:9$


Correct Option: C
Explanation:

There are two charges $+2\mu C$ and $-3\mu C$. The ratio of forces acting on them will be $F=\dfrac { { q } _{ 1 }{ q } _{ 2 }K }{ { r }^{ 2 } } $

$\dfrac { { F } _{ 1 } }{ { F } _{ 2 } } =\dfrac { { q } _{ 2 } }{ { q } _{ 1 } } =\dfrac { 3 }{ 2 } $ or  ${ F } _{ 1 }:{ F } _{ 2 }=3:2$

A light beam travelling in the x-direction is described by the electric field ${ E } _{ y }=(300V{ m }^{ -1 })sin\quad \omega (t-x/c).$ An electron is constrained to move along the y-direction with a speed of $2.0\times  {10}^7 { m }^{ -1 }$ Find the maximum electric force and the maximum magnetic force on the electron

  1. $4.8\times {10}^{-17} N, zero$

  2. $4.2\times {10}^{-18} N, 1.8\times 10^{-8}N$

  3. $4.8\times {10}^{-17} N, 3.2\times 10^{-18}N$

  4. Zero, Zero


Correct Option: A
Explanation:
A light beam travelling 
${ E } _{ y }=\left( 300V/m \right) sinw\left( t-x/c \right) $.
$V=2.0\times { 10 }^{ 7 }{ m }^{ -1 }$
${ B } _{ 0 }=\dfrac { { F } _{ 0 } }{ C } =\dfrac { 300 }{ 2\times { 10 }^{ 7 } } =150\times { 10 }^{ -7 }T$
${ F } _{ m }={ B } _{ 0 }qV$
       $=9.1\times { 10 }^{ -31 }\times 150\times { 10 }^{ -7 }\times 2\times { 10 }^{ 7 }$
       $=2.8\times { 10 }^{ -28 }\times 2$
       $=4.8\times { 10 }^{ -17 }N$
magnetic force $=0$
because they are perpendicular to each other.

Two charges Q and -2Q are placed at some distance. the locus of points in the plane of the charges where the potential is zero will be

  1. Straight line

  2. Circle

  3. Parabola

  4. ellipse


Correct Option: C
Explanation:
Two charges $Q$, $-2Q$
some distance
Potential $=0$
hence,
$\dfrac { 1 }{ 4\pi { \epsilon  } _{ 0 } } \times \dfrac { Q\times \left( -2Q \right)  }{ R } =0$
When we use it the parabolic condition then,
${ y }^{ 2 }=4ax\quad \longrightarrow \left( 1 \right) $
Now,
$\dfrac { 1 }{ 4\pi { \epsilon  } _{ 0 } } \times \dfrac { Q\times 2Q }{ R } =0$
$\dfrac { { 2Q }^{ 2 } }{ R } =0\quad \longrightarrow \left( 2 \right) $
Hence, equating $(1)$ and $(2)$ and we get, the system is getting parabola.

Force of attraction between two point charges $Q$ and $-Q$ separated by $d$ meter is $F _e$. When these charges are placed two identical sphere of radius $R=0.3\ d$ whose centries are $d$ meter apart the force of attraction between them is 

  1. Greater than $F _{e}$

  2. Equal to $F _{e}$

  3. Less than $F _{e}$

  4. None of these


Correct Option: B
Explanation:

Force of attraction between two point charges $Q$ and $-Q$ separated by $d$.

Force ${ F } _{ e }$
radius $=R=3d$
That is also equal to ${ F } _{ e }$ because the distance is same hence force is also same.

Two lithium nuclei in a lithium vapour at room temperature do not combine to form a carbon nucleus- because:

  1. a lithium nucleus is more tightly bound than a carbon nucleus

  2. carbon nucleus is unstable particle

  3. it is not energetically favourable

  4. coulomb repulsion does not allow the nuclei to come very close


Correct Option: D
Explanation:

Two lithium nuclei in a lithium vapor can combine only if vapor is heated to a very high temperature. so that the nuclei acquire high kinetic energy to penetrate the coulomb barrier. The vapor is also compressed to a very high pressure.

When a negatively charged ebonite rod is brought near a negatively charged and freely suspended ball, then the ball :

  1. gets repelled

  2. attracted

  3. is not affected

  4. none of these


Correct Option: A
Explanation:

Answer is A.

When two like charges are brought closer, they repel and when two unlike charges are brought closer, they attract each other.
Hence, when a negatively charged ebonite rod is brought near a negatively charged and freely suspended ball, then the ball gets repelled.

When a comb is rubbed with hair, it attracts paper bits. Choose the right explanation:

  1. Bits of paper gets attracted due to gravitational force

  2. Due to electromagnetic effect, bits of paper are attracted

  3. Comb gets charged by friction and attracts bits of paper

  4. None of these


Correct Option: C
Explanation:

When comb is rubbed to hair, it induces negative charge due to friction. When it is brought close to paper bits, they get polarized and the positive part sticks to the comb due to electrostatic attraction. 

In the thunderstorm, the charges accumulate near the upper edges of clouds are

  1. negatively charged

  2. positively charged

  3. neutral

  4. none of these


Correct Option: B
Explanation:

We have to find the nature of charges on upper edges of clouds in a thunderstorm, the air currents move upwards while the water droplets move downward. This vigorous movement causes separation of charges. This leads to the positive charges collected near the upper edges of clouds and the negative charges to accumulate near the lower edges of the clouds.

The safety fuse should have

  1. high resistance and high melting point

  2. high resistance and low melting point

  3. low resistance and high melting point

  4. low resistance and low melting point


Correct Option: B
Explanation:

The safety fuse should have high resistance and low melting point.


Option B is correct.

Charge 1 attracts Charge 2, Charge 2 repels Charge 3, and Charge 3 attracts Charge 4. Which of the following option must hold good for the given condition of four point charges? 

  1. Charge 1 attracts Charge 4

  2. Charge 2 attracts Charge 3

  3. Charge 1 repels Charge 3

  4. Charge 2 repels Charge 4

  5. Charge 1 repels Charge 4


Correct Option: E
Explanation:

If charge 1 is positive and charge 2 is negative, then charge 1 and 2  will attract. As charge 2 and 3 repels so charge 3 should be negative. Since charge 3 and 4 attracts so charge 4 should be positive. Thus, charge 1 and 4 both are same charge so they will repel. If you take charge 1 is negative and 2 is positive similarly you get 4 is negative so 1 and 4 both have same charge. 


Electric force can be_______

  1. always attractive

  2. always repulsive

  3. attractive or repulsive

  4. None of these


Correct Option: C
Explanation:

Electric force can be either attractive or repulsive .

Same charge repel each other while unlike nature of charge attract each other.

Answer-(C)

Two copper spheres, $A$ and $B$, are identical in all respect but A carries a charge of $-3 \mu C$ whereas $B$ Is charged to $+1 \mu C$. The two spheres are brought together until they touch and then separated by some distance. Which of the following statements is true concerning the electrostatic force $F$ between the spheres?

  1. $F = 0$ as one of the spheres is uncharged

  2. $F = 0$ as both the spheres are uncharged

  3. $F$ is attractive

  4. $F$ is repulsive.


Correct Option: D
Explanation:

Charge on $A^{+}$ sphere $=-3$ $uC$

Charge on $B$ sphere $=+1$ $uC$
When they are connected the charge get redistributed, i.e.
$\Rightarrow$ Charge on both sphere $=\dfrac{-3+1}{2}$ $uC=-1$ $uC$
So charge on either sphere $=-1$ $uC$
Therefore, After connecting charge on sphere $A=-1$ $uC$
After connecting charge on sphere $B=-1$ $uC$
Therefore, there will be a repulsive force between the sphere because of like charges.

What happens when some charge is placed on a soap bubble?

  1. Its radius decreases

  2. Its radius increases

  3. The bubble collapses

  4. None of the above


Correct Option: B
Explanation:

The radius of soap bubble increases due to inter-electronic repulsion.
Note that, the bubble may also explode if excess charge is large enough.

The potential at a point $(x, 0, 0)$ is given by $V = \left(\dfrac{1000}{x} + \dfrac{1500}{x^2} + \dfrac{500}{x^3}\right)$. The intensity of the electric field at $x = 1$ will be

  1. $550 V/m$

  2. $55 V/m$

  3. $55000 V/m$

  4. $5500 V/m$


Correct Option: D
Explanation:
$V=(\cfrac{1000}{x}+\cfrac{1500}{x^{2}}+\cfrac{500}{x^{3}})$
We know that, $E=\cfrac{-dv}{dr}$
So,
$E=\cfrac{-d(\cfrac{1000}{x}+\cfrac{1500}{x^{2}}+\cfrac{500}{x^{3}})}{dx}$   at $x=1$
$=-[\cfrac{(-1000)}{x^{2}}-\cfrac{2\times 1500}{x^{3}}-\cfrac{3\times 500}{x^{4}}] _{x=1}$
$=1000+3000+1500=5500\,V/m$

Consider two balls having same kind of charge on them. Identify the correct statement:

  1. They will repel one another.

  2. They will attract one another.

  3. They might attract one another.

  4. They will not have any effect on one another.


Correct Option: A
Explanation:

Two bodies having same nature of charge repel each other.


Answer-(A)

Five ball numbered $1$ to $5$ are suspended using separate threads. Pairs $(1,2)$, $(2,4)$ and $(4,1)$ show electrostatic attraction while pairs $(2,3)$, $(4,5)$ show repulsion. Therefore, ball $1$ must be

  1. neutral

  2. metallic

  3. positively charged

  4. negatively charged


Correct Option: A

If a comb is rubbed on dry hairs, and then brought near paper pieces, it :

  1. attracts paper

  2. repels paper

  3. remains indifferent to paper

  4. either attracts or repels paper


Correct Option: A
Explanation:

If we bring small bits of paper near a rubber (or plastic) comb, it is found that the comb does not attract the bits of paper. But if the same comb is first rubbed on dry hairs and then it is brought near the paper pieces, it attracts them.

True or False?
S1: Similar charge attracts each other.
S2: Similar charge repels each other.

  1. True, True

  2. True, false

  3. False, True

  4. false, false


Correct Option: C
Explanation:

There are 2 types of electrical charges - positive and negative - are said to be opposite types of charge. Consistent with our fundamental principle of charge interaction, a positively charged object will attract a negatively charged object. Oppositely charged objects will exert an attractive influence upon each other. In contrast to the attractive force between two objects with opposite chargess, two objects that are of like charge will repel each other. That is, a positively charged object will exert a repulsive force upon a second positively charged object. This repulsive force will push the two objects apart. Similarly, a negatively charged object will exert a repulsive force upon a second negatively charged object. Objects with like charge repel each other.
Hence, the statement is false.

State whether true or false:

Like charges attract each other.

  1. True

  2. False


Correct Option: B
Explanation:

Like charges repel each other whereas unlike charges attract each other.

Hence, the correct answer is option B.

State whether true or false:

Unlike charges attract each other.

  1. True

  2. False


Correct Option: A
Explanation:

Answer is A.

When two like charges are brought closer, they repel and when two unlike charges are brought closer, they attract each other.
Hence, unlike charges attaract each other and the statement is true.

What happens when some charge is placed on a soap bubble?

  1. Its radius decreases

  2. Its radius increases

  3. The bubble collapses

  4. None of these


Correct Option: B
Explanation:

The radius of soap bublle increases because of outward force acting on the bubble due to charging

What do you understand by the static or frictional electricity ?

  1. Discarging of two bodies on rubbing them together is called static or frictional electricity.

  2. Charging of two bodies on rubbing them together is called static or frictional electricity.

  3. Electricity which is static is called static or frictional electricity.

  4. Electricity on high friction bodies is called static or frictional electricity.


Correct Option: B
Explanation:

Static electricity is produced when a suitable combination of substances (e.g., glass rod and silk, ebonite rod and cat's skin, sealing wax and wool) are rubbed together and get electrified due to friction.

A negatively charged ebonite rod is brought near the glass rod which has been robbed on silk. State your observation between them

  1. Attraction

  2. Repulsion

  3. No change

  4. cant say


Correct Option: A
Explanation:

Rubbing the glass rod with the silk makes it lose electrons, so glass rod becomes positively charged. When a negatively charged ebonite rod is brought near the glass rod it attract each other as unlike charges attract each other.

- Hide questions