ELECTRIC CHARGES AND FIELDS , CLASS XII , MCQ Part 1

          MULTIPLE CHOICE QUESTIONS

 

MCQ Questions for Class XII Physics electric charges and fields with Answers.
Students can solve NCERT Class XII Physics electric charges and fields Latest Exam Pattern Multiple Choice Questions with Answers to know their preparation level.

1. An electric dipole placed in a non-uniform electric field will experience:                            

(a) Only a force

(b) Only a torque

(c) Both force and torque 

(d) Neither force nor torque  

Answer: d

2. Let N1 be the number of electric field lines going out of an imaginary cube of side a that encloses an isolated point charge 2q and N2 be the corresponding number for an imaginary sphere of radius a that encloses an isolated point charge 3q. Then (N1/N2) is:

(a) 1/π

(b) 2/3

(c) 9/4

(d) π

Answer: b

3. A charge Q is placed at the centre of the line joining two charges q and q. The system of the three charges will be in equilibrium if Q is:

(a) + q/3

(b) – q/3

(c) + q/4

(d) – q/4

Answer: d 

4. The electric flux of an electric field  through an area is given by:


5. Two point charges + 16q and – 4q are located at x = 0 and x = L. The location of the point on x- axis at which the resultant electric field due to these charges is zero, is :

(a) 8L

(b) 6L

(c) 4L

(d) 2L

Answer: d

 6.  An electric dipole of dipole moment 4 × 10-5 C m, kept in a uniform electric field of 10-3 NC-1, experiences a torque of 2 × 10-8 N m. The angle that the dipole makes with the electric field is:

(a) 30°

(b) 45°

(c) 60°

(d) 90°

Answer: d

 

7. Three identical charges are placed on the x-axis from left to right with adjacent charges separated by a distance d. The magnitude of the force on a charge from its nearest neighbour charge is F. Let î be the unit vector along + x-axis, then the net force on each charge from left to right is:

(a)  ( 2Fî , - 2Fî , 2Fî )

(b)  ( Fî, 0, FÎ )

(c) ( -5/4 FÎ , 0 , + 5/4 FÎ )

(d) ( 2 Fî , 0 , 2FÎ )

Answer: c

 8. A negatively charged object X is repelled by another charged object Y. However, an object Z is attracted to object Y. Which of the following is the most possibility for the object Z?

(a) Positively charged only.

(b) Negatively charged only.

(c) Neutral or positively charged.

(d) Neutral or negatively charged

Answer: c

 9. In an experiment, three microscopic latex spheres are sprayed into a chamber and charged with charges + 3e, + 5e, and - 3e respectively. All three spheres came in contact simultaneously for a moment and got separated. Which one of the following are possible values for the final charge on the spheres?

(a) + 5e, - 4e, + 5e

(b) + 6e, + 6e, -7e

(c) - 4e, + 3.5e, + 5.5e

(d) + 5e, - 8e, + 7e

Answer: b

 10. An object has a charge of 1 C and gains 5.0 x 1018 electrons. The net charge on the object becomes

(a) - 0.80 C

(b) + 0.80 C

(c) + 1.80 C

(d) + 0.20 C

Answer: d

11.  A square sheet of side 'a' is lying parallel to the XY plane at z = a. The electric field in the region is Ê= cz2 k. The electric flux through the sheet is

(a) a4c

(b) 1/3 a3c

(c) 1/3 a4c

(d) 0

Answer: a


12. Three charges q, - q, and q0 are placed as shown in the figure. The magnitude of the net force on the charge qo at point O is, [k=1/4π ε0 ]






Answer: c

13. Four objects W, X, Y, and Z, each with charge + q are held fixed at four points of a square of side d as shown in the figure. Objects X and Z are on the midpoints of the sides of the square. The electrostatic force exerted by object W on object X is F. Then the magnitude of the force exerted by object W on Z is



(a) F/7

(b) F/5

(c) F/3

(d) F/2

Answer: b

 14. Two point charges +8q and -2q are located at x = 0 and x=L respectively. The point on x-axis at which net electric field is zero due to these charges is

(a) 8L
(b) 4L
(c) 2L
(d) L

Answer: c

 15. Two point charges placed in a medium of dielectric constant 5 are at a distance r between them, and experience an electrostatic force 'F'. The electrostatic force between them in  a vacuum at the same distance r will be

(a) 5F

(b) F

(c) F/2

(d) F/5

Answer: a

 

16. Which statement is true for Gauss's law?

(a) All the charges whether inside or outside the Gaussian surface contribute to the electric flux.

(b) Electric flux depends upon the geometry of the Gaussian surface.

(c) Gauss theorem can be applied to a non-uniform electric field.

(d) The electric field over the Gaussian surface remains continuous and uniform at every point.

Answer: c

17. A cylinder of radius r and length l is placed in a uniform electric field parallel to the axis of the cylinder. The total flux for the surface of the cylinder is given by

(a) Zero

(b) πr2

(c) Eπr2

(d) 2Eπr2

Answer: a

18. Two parallel large thin metal sheets have equal surface densities of 26.4 ×10-12 C/m2 of opposite signs. The electric field between these sheets is

(a) 1.5 N/C

(b) 1.5×10-16N/C

(c) 3×10-10N/C

(d) 3 N/C

Answer: d

 19. Consider an uncharged conducting sphere. A positive point charge is placed outside the sphere.  The net charge on the sphere is then,

(a) Negative and uniformly distributed over the surface of a sphere.

(b) Positive and uniformly distributed over the surface of a sphere.

(c) Negative and appears at a point on the surface of a sphere closest to the point charge.

(d) Zero.

Answer: d        
 
20.  A small object with charge q and weight mg is attached to one end of a string of length 'L' attached to a stationary support. The system is placed in a uniform horizontal electric field 'E, as shown in the accompanying figure. In the presence of the field, the string makes a constant angle θ with the vertical. The sign and magnitude of q





(a) Positive with magnitude mg/E

(b) Positive with magnitude (mg/E) tanθ
(c) Negative with magnitude mg/E tanθ
(d) Positive with magnitude E tanθ /mg

Answer: b   

 21. When air is replaced by a dielectric medium of dielectric constant K, the force of  attraction between two charges q1 and q2 separated by a finite distance 'd’ 

(a) decreases K times.

(b) Increases K times.

(c) Remains unchanged.

(d) Decreases k2 times

Answer: a

 22. Two spherical conductors B and C having equal radii and carrying equal charges in them repel each other with a force F when kept apart at some distance. A third spherical conductor having same radius as that of B but uncharged is brought in contact with B, then brought in contact with C, and finally removed away from both. The new force of repulsion between B and C is                                                                                                                                                                               

(a)  F/4
(b)  3F/4
(c)  F/8
(d)  3F/8

Answer: d

 

23. A charge q is placed at the centre of the line joining two equal charges Q. The system of the three charges will be in equilibrium, if q is equal to                                                                                       


(a)  - Q/2

(b)  – Q/4

(c)  + Q/4

(d)  + Q/2


Answer: b
 
24. ABC is an equilateral triangle. Charges of + q are placed at each corner. The electric field at O will be  







Answer: c                                        

 25. The electric charges are distributed in a small volume. The flux of the electric field through a surface of radius 10cm surrounding the total charge is 20Vm. The flux over a concentric sphere of radius 20cm will be.

(a) 20 Vm

(b)  25 Vm

(c)  40 Vm

(d)  200 Vm

Answer: a

 

26. A hollow cylinder has a charge q coulomb within it. If ɸ is the electric flux in units of V-m associated with the curved surface B, the flux linked with the plane surface A in units of V-m will be




Answer: d        


27 A square surface of side L in the plane of the paper is placed in a uniform electric field E  in the given figure acting along the same plane at an angle Q with the horizontal side of the square as shown in the figure. The electric flux linked to the surface, in units of volt-m, is



(a)  EL2 sinθ

(b)  Zero

(c)  EL2

(d) EL2cos θ

Answer: a
 
Q.28. A charge Q is placed at each of the opposite corners of a square. A charge q is placed a teach of the other two corners. If the net electrical force on Q is zero, then O/q equals

(a) -1

(b) 1

(c)   -1/√2

(d)  -2√2

Answer: d
 
29. Two charges q1 and q2, separated by a distance 'r’ in air exert a force F on one another. If a copper plate of thickness r/2 is placed between the charges, the effective forces will be:


(a) 2F


(b) 4F


(c) F/2


(d) 0


Answer: d
 
30. Which of the following is not a unit of electric field?

(a) NC-1


(b) Vm-1


(c) j C-1m-1


(d) j C-1


Answer: d
 
31. In the given figure shows electric field lines corresponding to an electric field E. Figure suggests that




(a) EA > EB > EC

(b) EA = EB = EC

(c) EA = EC > EB

(d) EA = EC < EB

Answer: c  

32. A hexagon of side 'a' has a charge 'a' a teach of its vertices. The electric field at the centre of the hexagon is

 

Answer: a

33. Two charges of 10uC and 20uC respectively replaced at points A and B separated by a distance of 60 cm. The distance of the point P from A, where the net electric field is zero, is


(a) 20 cm


(b) 30 cm


(c) 40 cm


(d) 15 cm
Answer: a
 
34. If Ea be the electric field of a short dipole at a point on its axial line and E, that on the equatorial line at the same distance, then 
                                                                                                     
(a) Ea= 2Ee


(b) Ee=2Ea


(c) Ea=Ee


(d) None of theses
Answer: a
 
35. A point P lies on the perpendicular bisector of a short electric dipole, of dipole moment p, at a distance r from the centre of dipole. The electric field at point P is proportional to


(a) p/r2


(b) 1/pr2


(c) p/r3


(d) p2/r3
Answer: c


36. Ten dipoles, each of dipole moment 'p', are placed inside a hollow sphere. The total electric flux coming out of the sphere will be


(a) 0


(b) 10p/Ɛo


(c) p/Ɛo


(d) 20p/Ɛo

Answer: a


37.  Electric field ‘E’ at a point situated at a normal distance ‘r’ from an infinitely long uniformly charged straight wire is proportional to

(a) E ∝ r

(b) E ∝ 1/r

(c) E∝ 1/r2

(d) E∝ 1/r3
Answer: b

38. Which of the following graphs represents the variation of electric field E due to a thin spherical shell of radius R as a function of the distance r from the centre of the shell,


Answer: b

39. If the electric flux entering and leaving an enclosed surface are o and respectively, the electric charge present within the surface is

(a) 1/Ɛo (ɸ1- ɸ2)

(b) 1/Ɛo (ɸ2 - ɸ1)

(c) Ɛo (ɸ1+ɸ2)

(d) Ɛo(ɸ2 - ɸ1)
Answer: d
 
40. Gauss' law is true only if electric force due to a given charge varies with distance 'r’ as

(a) r-2

(b) r-3

(c) r2

(d) r-1
Answer: (a)


 


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