25 MCQs | Physics | Class XII | Electric Charges and Fields

 

1.    Which of the following statements is wrong with respect to electrostatics?

a)      Charge on any object is an integral multiple of an electronic charge

b)     Charge is conserved

c)      A stationary charge has both electric and magnetic field around it

d)     There is an electric field around an isolated charge at rest.

 

2.    Two point charges in air at a distance of 20 cm from each other interact with a certain force. At what distance from each other should these charges be placed in oil of relative permittivity 5 to obtain same force of attraction.

a)      8.94 X 10-2 m

b)     0.894 X 10-2 m

c)      89.4 X 10-2 m

d)     8.94 X 102 m

 

 

3.    Two free positive charges 4q and q are at a distance l apart. What charge Q is needed to achieve equilibrium for the entire system and where should it be placed from charge q.

a)      Q=4q/9(negative) at l/3

b)     Q=4q/9(positive) at l/3

c)      Q=q(positive) at l/3

d)     Q=q(negative) at l/3

 


4.    A free proton and free electron are placed in uniform electric field .

Assertion: acceleration of electron will be more than proton.

Reason: As F=qE, Force will be same on both particles irrespective of their masses.

  a)   Assertion and Reason are True, and Reason is not correct explanation of Assertion

            b)  Assertion and Reason are True, and Reason is correct explanation of Assertion

            c) Assertion is True, Reason is False

            d) Assertion is False, Reason is True

 


5.    Assertion: No two electric field lines can intersect each other.

Reason: There can be two directions possible of an electric field at any point.

  a)   Assertion and Reason are True, and Reason is not correct explanation of Assertion

            b)  Assertion and Reason are True, and Reason is correct explanation of Assertion

            c) Assertion is True, Reason is False

            d) Assertion is False, Reason is True 

 

 

6.    If electric flux through a closed surface is zero. It means that:

 a)   the net charge inside the surface is zero.

            b)  the net charge inside the surface is zero.

            c)  The electric field is necessarily zero at all points on the surface

            d)  No charge exists outside the surface          
 


7.    Two charges 10 pC and 5 pC are placed 20 cm apart. The ratio of Coulomb’s force experienced by there is:

a)      2:5

b)     1:1

          d)  None of these

 

 

8.    A sphere ‘P’ of mass 6.4 × 10-15 kg is hanging between the two charged parallel plates as shown in figure. How many electrons can be added or removed from the sphere so that it still remains hanging?

 


a)      8 electrons can be added

b)     16 electrons can be removed

c)      8.5 electrons can be removed

d)     8 electrons can be removed

 

 

9.    Which of the following method is an indirect method of charging ?

a)     Charging by induction

b)     Charging by physical contact

c)     Charging by friction

d)     None of these

 

 

10. The force between two point charges __________when dielectric constant of the medium in which they are held increases.

a)     decreases

b)     increases

c)     remains unaffected

    d)     None of the above 

 

 

11. The number of electric lines of force that radiate outward from 1C charge is ___________.

a)     1.13 X10 11

b)     1.13 X 10 9

c)      9 X 109 

d)     9 X 1011 

 

 

12. Which of the following statements is not true about Gauss’s law?

a)     Gauss’s law is true for any closed surface.

b)     The term q on the right side of Gauss’s law includes the sum of all charges enclosed by the surface.

c)     Gauss’s law is not much useful in calculating electrostatic field when the system has some symmetry.

d)     Gauss’s law is based on the inverse square dependence on distance contained in the coulomb’s law

 

 

13. The SI unit of electric flux is:

a)     N C-1 m-2

b)     N C m-2

c)     N C-2 m2

d)     N C-1 m2

 

 

14. The ratio of electric force between two electrons to the gravitational force between them is of the order:

a)     1042

b)     1039

c)     1036

d)     1

 

 

15. If a charge is moved against the Coulomb force of an electric field , then

a)      Work is done by the electric field

b)     Energy is used from some outside source

c)      Strength of the field is decreased

d)     Strength of the system is decreased

 

 

16.  The electric intensity due to a dipole of length 10 cm and having a charge of 500mC , at a point on the axis at a distance 20 cm, from one of the charges in air, is:

a)      6.25 X 107 N/C

b)     9.28 X 107 N/C

c)      13.1 X 1011 N/C

d)     20.5 X 107 N/C

 

 

17.  The value of charge q at the center of two equal and like charges Q so that the three are in equilibrium is:

a)     Q

b)     +Q/4

c)     -Q/4

d)     Q/2

 

 

18. Electric filed is zero in case of a charged conducting shell at any:

a)     Interior point

b)     Exterior point

c)     On surface

d)     None of above

 

 

19.  The electric flux through the surface : 


a)      (iv) is the largest

b)     (iii) and (ii) are equal but larger than (ii)

c)      (i) is the least

d)     is same in all cases.

 

 

20.  A body is positively charged, It implies that :

a)      There is only positive charge in the body.

b)     There is both positive and negative charge in the body but the positive charge is more than the negative charge.

c)      There is both positive and negative charges but positive charge lies in outer regions of the conductor.

d)     Negative charge is displaced from its position.

 


21. Two point charges are separated by a certain distance. If +Q>+q, then in between the charges , E is zero at a point:

a)      Closer to +Q

b)     Closer to +q

c)      Exactly at mid point of Q and q

d)     Nowhere on the line joining Q and q

 

 

22.   An electric dipole is kept in a non uniform electric field. It experiences :

a)      Both Torque and Force

b)     Torque but not Force

c)      Force but not Torque

d)     Neither Torque not Force

 

 

23.  Dielectric strength of a metal is :

a)      0

b)     1

c)      -1

d)     Infinite

 

 

24. Each of the two point charges are doubled and their distance is halved. Force of interaction becomes p times, w here p is:

a)     1

b)     4

c)     1/16

d)     16

 

 

25.  Which of the statements is True for a short electric dipole?

a)      Electric field at a distance ‘r’ on axial point is double the Electric field at same distance on equatorial point.

b)     Electric field at a distance ‘r’ on equatorial point is double the Electric field at same distance on axial point.

c)      Net translating force on a dipole is non zero in a uniform electric field.

d)     None of above

 

 

Answers:

1.   c)      A stationary charge has both electric and magnetic field around it

2.   a)     8.94 X 10-2 m

3.   a)      Q=4q/9(negative) at l/3

4.   b)    Assertion and Reason are True, and Reason is correct explanation of Assertion

5.   c)   Assertion is True, Reason is False

6.   a)   the net charge inside the surface is zero.

7.   b)   1:1

8.   d)    8 electrons can be removed

9.   a)    Charging by induction

10. a)    decreases

11. a)     1.13 X10 11

12. c)     Gauss’s law is not much useful in calculating electrostatic field when the system has some      

              symmetry.

13. d)     N C-1 m2

14. a)     1042

15. b)     Energy is used from some outside source

16. a)      6.25 X 107 N/C

17. c)     -Q/4

18. a)     Interior point

19. d)     is same in all cases.

20. b)     There is both positive and negative charge in the body but the positive charge is more than 

              the  negative charge.

21. b)     Closer to +q

22. a)      Both Torque and Force

23. d)     Infinite

24. d)     16

25. a)      Electric field at a distance ‘r’ on axial point is double the Electric field at same distance on 

               equatorial point.




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