Electric Charges and Fields Mock Test – Class 12 Physics

1. A charge distribution has spherical symmetry, but the charge enclosed by a spherical Gaussian surface of radius changes with . The correct Gauss-law strategy is to use

2. Two fixed charges and lie on a straight line. A small positive charge is placed somewhere between them. For the net force on the small charge to be zero, it should be

3. A source charge produces electric field at distance . If the source charge becomes and the medium is changed to a dielectric of constant , with the same distance , the new field magnitude is

4. Study the statements about a charged conductor in electrostatic equilibrium.
I. The electric field inside the conductor is zero.
II. The electric field just outside the surface is normal to the surface.
III. A tangential electric field at the surface would make free charges move.
IV. The field just outside every charged conductor surface is always zero.
The supported statements are

5. For a negatively charged spherical shell, the electric field at an outside point is directed

6. A closed Gaussian surface is drawn entirely inside the material of a conductor in electrostatic equilibrium. The net charge enclosed by this Gaussian surface must be

7. A charge is placed at the centre of a cube. The flux through one face is . The charge is

8. 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

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

10. Electric field lines for two equal positive charges show a gap-like region between the charges where lines bend away from each other. This happens because

11. A final comparison is made between electric force, electric field, electric flux, and Gauss’s law. The correctly paired statement is

12. A charge is placed at the centre of a spherical Gaussian surface of radius . The electric field magnitude on the surface is

13. A student applies Gauss’s law to a closed surface and uses the total charge inside and outside the surface in . The correction is that means

14. Three charges lie on the -axis. A charge at the origin experiences toward due to a charge on the left and toward due to a charge on the right. The net force on is

15. An infinite line charge of density and an infinite plane sheet of density produce equal field magnitudes at a distance from the line. The value of is

16. Study the table about force and field directions. Identify the row that needs correction.

17. Study the table about electroscope observations and identify the row that does not fit the usual explanation.

18. A charged body is brought near a neutral conductor, and the conductor moves slightly toward it. This motion should not be confused with charge movement because

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

20. In a square of side , two charges are fixed at the left two corners and two charges are fixed at the right two corners. A positive charge is placed at the centre. The net force on is directed

21. Two charges are changed from and to and , with separation unchanged. The new force magnitude is

22. Study the table for a fixed pair of charges in the same medium and identify the row that does not follow Coulomb proportionality.

23. A dipole of moment is in a uniform field . The work required by an external agent to rotate it slowly from stable equilibrium to unstable equilibrium is

24. A charge pair is tested in two media at the same separation. Medium P has , and medium Q has . If the vacuum force is , the ratio of force in P to force in Q is

25. Two claims are made about a neutral conductor placed near a charged body.
I. Charges inside the conductor may redistribute even without contact.
II. Redistribution of charges always means the conductor has gained a non-zero net charge.
III. In a metal, mobile electrons are responsible for the easy redistribution of charge.
The valid claims are

26. The final sign of a conductor charged by induction is opposite to the sign of the inducing body because the conductor

27. Assertion: Electric flux is a scalar quantity, but it may be positive, negative, or zero.
Reason: Electric flux is obtained from the dot product , whose sign depends on the angle between the two vectors.

28. For two fixed charges, the graph of versus is best described as

29. During charging by friction, a glass rod loses electrons to silk. For the combined system of glass rod and silk, the total charge is unchanged because

30. A Coulomb-law calculation uses , , , and . The force magnitude is

31. 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

32. Coulomb’s law and Newton’s law of gravitation are similar in the sense that both

33. For an infinite uniformly charged plane sheet with surface charge density , the electric field is directed

34. The relation says that when the separation is doubled while the charges stay the same, the force becomes

35. 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

36. Two identical isolated conducting spheres initially carry and . After touching and separating, one of them is touched to a third identical neutral sphere and then separated. The final charge on the first sphere after the second contact is

37. The potential energy of an electric dipole in a uniform electric field is

38. Study the table and identify the row that contains a wrong interpretation.

39. An electric field graph for a source is given by . If the graph of against has slope , and , the source and observation line are best identified as

40. In a uniform electric field directed toward the right, a small positive charge released from rest initially accelerates

41. A rectangular surface has area . It is placed in a uniform electric field such that the angle between and is . The electric flux is

42. A graph description says that for two fixed point charges in vacuum, increasing makes decrease rapidly, and doubling gives one-fourth the force. This behaviour is called

43. A charge is placed at the centre of a square. Four identical positive charges are fixed at the four corners. If the centre charge is removed, the electric field at the centre due to the four corner charges is

44. Charges , , and a small positive charge lie on a straight line. The charge is at , is at , and is placed at between them so that the net force on is zero. The value of is

45. A spherical conductor of radius has charge . A point charge of mass is released just outside the surface. Ignoring gravity, its initial acceleration magnitude is

46. 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

47. A charge distribution is described by the following data.

The mismatched row is

48. A point charge produces field at distance in vacuum. The source charge is doubled, the distance is tripled, and the space is filled with a dielectric of constant . The new field magnitude is

49. A force on due to is calculated using from to . The product is negative. The vector force is therefore

50. A cylindrical Gaussian surface of radius and length surrounds an infinitely long line charge of density . The charge enclosed by the cylinder is