Electric Charges and Fields Mock Test – Class 12 Physics

1. Charge is fixed at , and charge is fixed at . Taking to the right, the direction of the force on due to is

2. In a one-dimensional setup, is at , and is at . Take . The force on due to is

3. A dipole in a uniform electric field has as the angle between and . The torque magnitude is maximum when is

4. A positive charge of mass is projected along a uniform electric field with speed . The minimum distance it travels before its speed becomes is

5. Three identical isolated conducting spheres have initial charges , , and . First, sphere P touches sphere Q and separates. Then sphere P touches sphere R and separates. The final charge on sphere P is

6. A neutral glass rod is rubbed with silk and becomes positively charged. If the rod has charge , the number of electrons lost by the rod is approximately .

7. A rubbed plastic comb attracts small paper bits. The attraction of the paper bits by itself does not prove that the paper bits were initially oppositely charged because

8. A uniformly charged spherical shell and an infinite line charge give equal electric fields at , where is measured from the shell centre and from the line respectively. At , the ratio is

9. The approximate value of Coulomb’s constant in vacuum is

10. A far equatorial point is chosen at distance from the centre of a dipole. If the dipole moment is doubled while remains the same, the equatorial field magnitude becomes

11. Electric field lines are drawn closer together in one region and farther apart in another. The closer spacing indicates that the electric field in that region is

12. Two very large parallel sheets carry equal and opposite surface charge densities and . In the region between the sheets, the electric fields due to the sheets

13. An insulating plastic strip is charged at one small region by rubbing. Compared with a metal strip, the charge on the plastic strip is more likely to remain near that region because

14. Two electrons repel each other electrostatically and attract each other gravitationally. The reason these two forces have opposite nature for the same pair is that

15. Assertion: The electric field at a point can be zero even when the point is near more than one charge.
Reason: Electric field is a vector quantity, so equal and opposite field contributions can cancel.

16. A graph of versus for a uniformly charged thin spherical shell of radius is compared with a graph for an infinite line charge. The correct comparison is

17. For a dipole in a uniform electric field, the potential energy is minimum when the angle between and is

18. A body becomes negatively charged after receiving electrons from another body. Conservation of charge requires that the other body

19. A point charge is inside a spherical Gaussian surface but not at its centre. The total flux through the sphere is still

20. Assertion: In charging by contact, a neutral conductor can acquire the same sign of charge as the charged conductor that touches it.
Reason: During contact, charge can flow and redistribute through the conducting connection.

21. Assertion: In electrostatic superposition, the net force can be zero even when individual forces are non-zero.
Reason: Vector forces can cancel when they have equal magnitudes and opposite directions.

22. A dipole is placed in two different regions.

The row that needs correction is

23. A graph is plotted between Coulomb force magnitude and for two fixed point charges in vacuum. The graph is a straight line through the origin. Its slope represents

24. A system contains charges , , , and . The expression that represents the net charge is

25. Gauss’s law relates the total electric flux through a closed surface to

26. A point charge produces an electric field at a point away in vacuum. Take . The field magnitude is

27. Assertion: Coulomb force and gravitational force both obey superposition.
Reason: In each case, the net force due to several sources is found by vector addition of individual force contributions.

28. Study the dipole statements below.
I. An electric dipole has zero net charge.
II. The dipole moment magnitude is charge magnitude multiplied by separation.
III. The dipole moment vector points from to .
IV. A dipole can have non-zero dipole moment even though its net charge is zero.
The supported statements are

29. A closed surface contains a charge , and a charge is placed outside it. The net flux through the closed surface is

30. A negatively charged rod is brought near, but does not touch, a neutral metal sphere on an insulating stand. The near side of the sphere becomes relatively positive. This happens because

31. A dipole is shown with at Point L and at Point R. The dipole moment direction is

32. At a far axial point of a dipole, the electric field is at distance . At a far equatorial point at distance from the same dipole, the field magnitude is

33. The leaves of a gold-leaf electroscope diverge when a charged body touches its metal cap because

34. A body has an excess of electrons compared with protons. In elementary electrostatics, the body is described as

35. A known positively charged rod is brought near the cap of a positively charged electroscope. The leaf divergence increases. The increase suggests that

36. A student compares , , and for a Gaussian surface. The correct statement is

37. A negative charge is placed just outside a positively charged conductor surface. The conductor’s local electric field is outward normal. The force on the negative charge is

38. Use the arrangement described below.

After moving the point to , the largest field belongs to the

39. For a curved surface in a non-uniform electric field, the electric flux is written as

40. A charge is placed at the centre of a rectangle. Equal positive charges are fixed at the two ends of one diagonal, and no charges are fixed at the other two corners. The net force on due to the two fixed charges is

41. Assertion: Total charge is found by algebraic addition, not vector addition.
Reason: Electric charge is a scalar quantity with sign.

42. A dipole has charges separated by . At a far axial point distance , the field magnitude is . If is doubled, is halved, and is doubled, the new far axial field is

43. A compound setup has a point charge at distance , an infinite line charge with density at distance , and an infinite plane sheet with density . Their field magnitudes at the same point are equal. The relation among , , , and is

44. Assertion: Electric charge is treated as a scalar quantity in elementary electrostatics.
Reason: Positive and negative signs of charge represent kinds of charge, not directions in space.

45. Assertion: In vector Coulomb-law calculations, changing the definition of the unit vector can change the algebraic sign in the formula but not the physical force.
Reason: The same physical vector must be obtained when the sign convention is used consistently.

46. Two light charged balls are suspended by insulating threads. When brought close, they move away from each other. The most suitable inference is that the balls

47. Three charge-density units are listed as , , and . The exponent of tells

48. A charge experiences forces along and along . The net force is

49. The table gives four claims about materials in electrostatics. Identify the claim that needs correction.

50. For two charges at position vectors and , the vector points