15 extra multiple-choice questions for Electrostatics (12th Standard Physics, Samacheer Kalvi), beyond the ones printed in the textbook — each with the correct option highlighted and a clear, worked explanation. Free to read in English and Tamil.
Q1
Which specific branch of electricity deals with the behavior and study of stationary charges at rest?
- A. Magnetostatics
- B. ElectrostaticsCorrect
- C. Electrodynamics
- D. Current Electricity
Explanation. Electrostatics is the fundamental branch of physics dedicated to investigating the properties and interactions of electric charges that are not in motion.
Q2
In the SI system of units, what is the approximate numerical value of the proportionality constant \(k\) used in Coulomb's law for free space?
- A. \(9 \times 10^9\) N m\(^2\) C\(^{-2}\)Correct
- B. \(8.85 \times 10^{-12}\) C\(^2\) N\(^{-1}\) m\(^{-2}\)
- C. \(1.6 \times 10^{-19}\) C
- D. \(6.63 \times 10^{-34}\) J s
Explanation. The proportionality constant \(k\) is defined as \(1 / (4\pi\epsilon_0)\), which yields a value of approximately \(9 \times 10^9\) N m\(^2\) C\(^{-2}\) when using SI units in a vacuum.
Q3
What is the standard SI unit used to measure the intensity of an electric field?
- A. Coulomb meter (C m)
- B. Newton per Coulomb (N C\(^{-1}\))Correct
- C. Joule per Coulomb (J C\(^{-1}\))
- D. Volt meter (V m)
Explanation. Electric field intensity is defined as the electrostatic force acting per unit test charge, making its SI unit Newtons per Coulomb.
Q4
Why is it physically impossible for two electric field lines to intersect each other in a region of space?
- A. Because they are always parallel to each other
- B. Because they would neutralize each other at that point
- C. Because the electric field would have two different directions at the same pointCorrect
- D. Because field lines only exist in one dimension
Explanation. Since the tangent to a field line gives the field's direction, an intersection would imply two different directions for the electric field at a single point, which cannot happen.
Q5
What is the conventional direction assigned to the electric dipole moment vector?
- A. From the positive charge to the negative charge
- B. Perpendicular to the axis joining the charges
- C. From the negative charge to the positive chargeCorrect
- D. Radially outward from the midpoint
Explanation. By definition, the electric dipole moment vector points along the axial line starting from the negative charge and ending at the positive charge.
Q6
At very large distances \(r\) from a dipole, how does the electric field magnitude on the axial line compare to the field magnitude on the equatorial plane at the same distance?
- A. They are exactly equal in magnitude
- B. The axial field is twice as strong as the equatorial fieldCorrect
- C. The equatorial field is twice as strong as the axial field
- D. The axial field is four times as strong
Explanation. The axial field magnitude is \(2p / (4\pi\epsilon_0 r^3)\) and the equatorial field magnitude is \(p / (4\pi\epsilon_0 r^3)\), showing the axial field is double the equatorial field at large distances.
Q7
How is the electrostatic potential difference between two points P and R defined?
- A. The work done by an external force to bring a unit positive charge from R to PCorrect
- B. The total electrostatic force acting between points R and P
- C. The product of the charge and the distance between the two points
- D. The potential energy stored in a single stationary point charge
Explanation. Potential difference is defined as the work per unit charge required to move a unit positive charge from a reference point to another point against the electric field.
Q8
What is the net work done when moving a test charge between any two points located on the same equipotential surface?
- A. Maximum work is done
- B. Work depends on the path taken
- C. Zero work is doneCorrect
- D. Work equals the product of charge and field
Explanation. Because the electric potential is identical at all points on such a surface, the potential difference is zero, meaning no work is required to move a charge across it.
Q9
According to Gauss's law, on what factor does the total electric flux passing through a closed Gaussian surface solely depend?
- A. The geometric shape and size of the surface
- B. The net electric charge enclosed within the surfaceCorrect
- C. The distribution of charges located outside the surface
- D. The velocity of the charges moving inside the surface
Explanation. Gauss's law states that total flux is proportional only to the net enclosed charge divided by the permittivity, and is independent of the shape or size of the enclosing surface.
Q10
In the context of electrostatic shielding, what is the value of the electric field inside a cavity of a conductor?
- A. It is equal to the external applied field
- B. It varies based on the shape of the cavity
- C. It is always zeroCorrect
- D. It depends on the material of the conductor
Explanation. Regardless of the external charges or fields, the electric field inside any cavity within a conductor at equilibrium is zero, a property used for protecting sensitive instruments.
Q11
What phenomenon occurs in a non-polar dielectric molecule when it is subjected to an external electric field?
- A. It loses its electrons and becomes ionized
- B. Its positive and negative charge centers coincide more perfectly
- C. It acquires an induced dipole momentCorrect
- D. It begins to flow like a metallic conductor
Explanation. The external field displaces the centers of positive and negative charges in opposite directions, creating a temporary dipole moment aligned with the field.
Q12
The SI unit of capacitance, the Farad, is named in honor of which renowned scientist?
- A. Charles Coulomb
- B. Alessandro Volta
- C. Michael FaradayCorrect
- D. James Clerk Maxwell
Explanation. Capacitance is measured in Farads (F), named after Michael Faraday to acknowledge his foundational experimental and theoretical work in electromagnetism.
Q13
What is the effect on the capacitance of a parallel plate capacitor when a dielectric material with relative permittivity \(\epsilon_r\) is inserted between its plates?
- A. The capacitance decreases by a factor of \(\epsilon_r\)
- B. The capacitance remains constant
- C. The capacitance increases by a factor of \(\epsilon_r\)Correct
- D. The capacitance becomes independent of plate area
Explanation. The dielectric polarizes and creates an internal field that opposes the external field, effectively allowing the capacitor to store more charge for the same voltage, thus increasing capacitance.
Q14
In an irregularly shaped charged conductor, why is the surface charge density highest at the regions with the sharpest points?
- A. Because the surface area is largest at sharp points
- B. Because the radius of curvature is smallest at sharp pointsCorrect
- C. Because the electric potential is highest at sharp points
- D. Because air resistance is lowest at sharp points
Explanation. Charge distribution on a conductor is such that the surface charge density is inversely proportional to the radius of curvature; sharp points have very small radii and thus high density.
Q15
Which two specific electrostatic phenomena are primarily utilized for the large-scale accumulation of charge in a Van de Graaff generator?
- A. Dielectric breakdown and Joule heating
- B. Electrostatic induction and action of pointsCorrect
- C. Coulomb repulsion and Magnetic torque
- D. Dipole polarization and Ohmic conduction
Explanation. The generator employs electrostatic induction to charge a moving belt and the action of points (corona discharge) to transfer that charge to a hollow metallic sphere.
