Electric field due to point charges, electric field lines, electric dipole and field due to a dipole - Question Bank

1. The electric field at a point P, which is very far from a dipole, is proportional to (1/r^n). What is the value of n?
A) 1
B) 2
C) 3
D) 4
2. An electric dipole is placed in a uniform electric field E. The potential energy of the dipole is given by U = -pE cos(theta), where p is the dipole moment and theta is the angle between p and E. The dipole is in stable equilibrium when theta is:
A) 0 degrees
B) 90 degrees
C) 180 degrees
D) Varies with E
3. The unit of electric field, Newton per Coulomb (N/C), is equivalent to:
A) Volt per meter (V/m)
B) Joule per Coulomb (J/C)
C) Ampere per meter (A/m)
D) Coulomb per meter (C/m)
4. The electric field lines for two identical positive charges are best described as:
A) Converging towards a point between them
B) Diverging outwards from a region between them
C) Straight lines emanating from each charge
D) Circular paths around each charge
5. The electric field at a point P due to a dipole is zero if P is:
A) At infinity
B) At the center of the dipole
C) On the axis of the dipole
D) On the perpendicular bisector at infinity
6. The electric field strength at a distance r from a point charge of magnitude Q is given by E = kQ/r^2. If the charge is -Q, the electric field at the same distance is:
A) E
B) -E
C) kQ/r
D) kQ^2/r^2
7. What is the work done in moving a charge from one point to another in an electric field?
A) Equal to the change in kinetic energy
B) Equal to the change in potential energy
C) Zero if the path is closed
D) Always positive
8. Electric field lines are imaginary and are used to visualize the electric field. They provide information about:
A) Direction only
B) Magnitude only
C) Both direction and magnitude
D) Potential difference only
9. The electric field at a point due to an electric dipole is proportional to the product of the dipole moment and the:
A) Distance from the dipole
B) Square of the distance from the dipole
C) Cube of the distance from the dipole
D) Inverse of the distance from the dipole
10. An electric dipole is placed in a uniform external electric field. The net force on the dipole is:
A) Always zero
B) Non-zero if the field is non-uniform
C) Non-zero if the dipole moment is not aligned with the field
D) Dependent on the magnitude of the charges
11. Which quantity is conserved for an isolated system of charges?
A) Total charge
B) Total energy
C) Total linear momentum
D) Total angular momentum
12. If the medium is changed from vacuum to a dielectric medium with dielectric constant K, the electric field due to a point charge:
A) Increases by a factor of K
B) Decreases by a factor of K
C) Remains unchanged
D) Becomes zero
13. Consider a dipole with charges +q and -q separated by 2a. The electric field at a distance r >> a along the axis is approximately:
A) kq/(r^2)
B) k(2q)/(r^2)
C) 2kqa/(r^3)
D) k(2qa)/(r^3)
14. The electric field lines are perpendicular to the surface of a:
A) Point charge
B) Electric dipole
C) Conductor in electrostatic equilibrium
D) Charged insulator
15. What is the dimensionality of the electric dipole moment?
A) [M^0 L^1 T^1 A^1]
B) [M^0 L^2 T^1 A^1]
C) [M^0 L^1 T^2 A^1]
D) [M^0 L^1 T^1 A^0]
16. The number of electric field lines passing through a surface is proportional to the:
A) Electric field strength
B) Area of the surface
C) Charge enclosed by the surface
D) Distance from the charge
17. The electric field due to a system of two equal and opposite charges (a dipole) at a point far away on the equatorial line is directed:
A) Along the equatorial line, towards the dipole
B) Along the equatorial line, away from the dipole
C) Parallel to the dipole axis, in the direction of the dipole moment
D) Parallel to the dipole axis, opposite to the direction of the dipole moment
18. If the distance between two charges of an electric dipole is '2a' and the charge is 'q', the dipole moment is:
A) q/2a
B) 2aq
C) q/(2a)
D) q * a
19. The electric field lines never form closed loops in electrostatics because:
A) Electric field is always conservative
B) Electric field is always non-conservative
C) Work done by electric field is always positive
D) Work done by electric field is always negative
20. The electric field at a very large distance from an electric dipole is proportional to:
A) p/r^2
B) p/r^3
C) p^2/r^3
D) p/r
21. An electric dipole is placed in a non-uniform electric field. It will experience:
A) Only a torque
B) Only a net force
C) Both a net force and a torque
D) Neither a net force nor a torque
22. If a point charge +q is placed at the origin, the electric field at point (x, y, z) is proportional to:
A) 1/r
B) 1/r^2
C) r
D) r^2
23. The electric field lines are closer where the electric field is:
A) Weaker
B) Stronger
C) Uniform
D) Zero
24. For an electric dipole, the electric field strength is maximum along:
A) The perpendicular bisector
B) The axis
C) A direction 45 degrees to the axis
D) The center of the dipole
25. The electric field at a point is zero. This implies that:
A) There is no net charge in the vicinity
B) There is no charge at that point
C) The net force on a test charge at that point is zero
D) All of the above
26. In a uniform electric field, the electric field lines are:
A) Diverging
B) Converging
C) Parallel and equally spaced
D) Curved
27. What is the unit of electric dipole moment?
A) Coulomb-meter (C·m)
B) Newton-meter (N·m)
C) Joule-meter (J·m)
D) Volt-meter (V·m)
28. The electric field due to a dipole at a point on its axis is directed:
A) Along the dipole axis, away from the center
B) Along the dipole axis, towards the center
C) Perpendicular to the dipole axis
D) Randomly depending on the distance
29. The electric field at a distance r from a point charge Q is given by E = kQ/r^2. If Q is doubled and r is halved, the new electric field will be:
A) E/4
B) E/2
C) 2E
D) 8E
30. Which of the following statements about electric field lines is incorrect?
A) They start from positive charges and end on negative charges.
B) They are continuous curves.
C) They intersect each other at points where the field is zero.
D) The tangent to a field line at any point gives the direction of the electric field at that point.
31. The electric field at a point is defined as the force per unit:
A) Positive test charge
B) Negative test charge
C) Charge density
D) Volume
32. Gauss's Law is a consequence of the inverse square law for the electrostatic force. The electric field due to a point charge follows an inverse square law, meaning it is proportional to:
A) r
B) r^2
C) 1/r
D) 1/r^2
33. The electric field lines of a dipole are:
A) Straight lines emanating from one charge and ending on the other
B) Closed loops
C) Curved lines starting from the positive charge and ending on the negative charge
D) Parallel lines
34. What is the net charge of an electric dipole?
A) Equal to the magnitude of one charge
B) Twice the magnitude of one charge
C) Zero
D) Dependent on the distance between charges
35. The density of electric field lines represents:
A) The direction of the electric field
B) The magnitude of the electric field
C) The potential difference
D) The charge enclosed
36. For a dipole, the electric field on the perpendicular bisector at a distance r from the center is proportional to:
A) 1/r
B) 1/r^2
C) 1/r^3
D) 1/r^4
37. The direction of the electric dipole moment vector is from:
A) Positive charge to negative charge
B) Negative charge to positive charge
C) The center of the dipole towards the positive charge
D) The center of the dipole towards the negative charge
38. Electric field lines never intersect because:
A) Electric field is always zero at intersection points
B) It would imply two directions of the electric field at the same point
C) They are repelled by each other
D) They are attracted to each other
39. If the distance from a point charge is doubled, the electric field strength at that point becomes:
A) Half
B) One-fourth
C) Double
D) Four times
40. The electric field strength at the center of an electric dipole is:
A) Maximum
B) Minimum (zero)
C) Equal to the field of one charge
D) Dependent on the surrounding medium
41. The electric field lines for a system of two equal positive charges are:
A) Converging at the midpoint
B) Diverging from the midpoint
C) Straight lines connecting the charges
D) Circular around each charge
42. The electric field at a point located far away from an electric dipole along its axis is proportional to:
A) 1/r
B) 1/r^2
C) 1/r^3
D) 1/r^4
43. What is the electric dipole moment?
A) The product of the charge and the distance between them
B) The sum of the charges multiplied by the distance
C) The difference between the charges multiplied by the distance
D) The square of the charge multiplied by the distance
44. The electric field lines due to a negative point charge are:
A) Radial and outwards
B) Radial and inwards
C) Circular and clockwise
D) Circular and counter-clockwise
45. An electric dipole consists of:
A) Two equal positive charges
B) Two equal negative charges
C) Two equal and opposite charges separated by a small distance
D) One large positive charge and one small negative charge
46. What is the direction of the electric field at a point due to a positive point charge?
A) Towards the charge
B) Away from the charge
C) Tangential to the position vector
D) Radial, but towards the charge
47. The magnitude of the electric field due to a point charge q at a distance r is proportional to:
A) 1/r
B) 1/r^2
C) r
D) r^2
48. Electric field lines originate from positive charges and terminate on:
A) Other positive charges
B) Negative charges
C) Neutral objects
D) The ground
49. What is the SI unit of electric field?
A) Volt per meter (V/m)
B) Newton per meter (N/m)
C) Coulomb per meter (C/m)
D) Joule per meter (J/m)
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