Free Electrostatics MCQs with Answers

• A. the product of the charges and inversely proportional to the distance between them
• B. the product of the charges and inversely proportional to the square of the distance
• C. the sum of the charges and the square of the distance
• D. the square of the product of the charges

Explanation: The inverse square dependence means doubling the separation quarters the force, exactly as in Newton's law of gravitation.

• A. half
• B. double
• C. four times
• D. one quarter

Explanation: Force varies as one over the square of the separation, so halving the distance multiplies the force by four.

• A. four times greater
• B. one quarter
• C. unchanged
• D. twice as great

Explanation: The medium appears in the denominator of Coulomb's law, so a relative permittivity of 4 reduces the force to a quarter of its vacuum…

• A. the force per unit positive charge placed at that point
• B. the work done in bringing a charge to that point
• C. the charge per unit area
• D. the potential at that point

Explanation: Field intensity is a vector measured in newtons per coulomb, equivalently volts per metre, and it points in the direction a positive test…

• A. proportional to q and to r
• B. proportional to q and inversely proportional to r squared
• C. independent of r
• D. proportional to r squared

Explanation: Dividing the Coulomb force by the test charge leaves E equal to kq over r squared, so the field also obeys an inverse square law and…

• A. can cross one another
• B. start on negative charges and end on positive charges
• C. never cross, because the field has only one direction at each point
• D. are always straight

Explanation: Two crossing lines would mean two different field directions at the same point, which is impossible for a single resultant vector.

• A. zero everywhere
• B. maximum at the centre
• C. equal to the field just outside
• D. directed towards the centre

Explanation: Charges on a conductor arrange themselves on the outer surface until the field inside cancels completely; any residual field would move…

• A. a vector measured in newtons per coulomb
• B. the work done per unit positive charge in bringing it from infinity to that point
• C. the force per unit charge
• D. the charge stored per unit voltage

Explanation: Potential is a scalar measured in volts, so potentials from several charges are added arithmetically with their signs rather than as…

• A. maximum
• B. zero
• C. negative
• D. equal to qV

Explanation: Work equals charge multiplied by the potential difference, and on an equipotential surface that difference is zero, so no work is done…

• A. one volt
• B. one joule
• C. 1000 volts
• D. one coulomb

Explanation: Since energy is charge multiplied by potential difference, one electron volt equals 1.6 times 10 to the minus 19 joules, the magnitude of…

• A. the charge stored per unit potential difference across the capacitor
• B. the energy stored per unit charge
• C. the charge multiplied by the voltage
• D. the potential difference per unit charge

Explanation: C equals Q over V, measured in farads, and it depends only on the geometry of the plates and the dielectric between them, not on how much…

• A. increasing the plate separation
• B. decreasing the plate area
• C. increasing the plate area and inserting a dielectric
• D. increasing the applied voltage

Explanation: Capacitance is proportional to the area and to the relative permittivity of the dielectric, and inversely proportional to the separation…

• A. the sum of the individual capacitances
• B. less than the smallest of them
• C. the reciprocal of the sum of the reciprocals
• D. always equal to one of them

Explanation: Parallel capacitors share the same voltage and their plate areas effectively add, so the capacitances add directly.

• A. QV
• B. half CV squared
• C. CV
• D. half QC

Explanation: The factor of one half appears because the voltage rises from zero to V as the capacitor charges, so the average voltage during the…

• A. increase
• B. decrease, because the capacitance rises while the charge is fixed
• C. stay the same
• D. become zero

Explanation: With the capacitor disconnected the charge cannot change, and since V equals Q over C, raising the capacitance must lower the voltage.

• A. midway between them
• B. at one of the charges
• C. outside the pair, beyond the smaller charge
• D. nowhere, since the field is never zero

Explanation: For like charges of equal magnitude the two fields are equal and opposite at the midpoint, so they cancel there.

• A. uniformly throughout its volume
• B. on its outer surface, concentrating most where the surface is sharply curved
• C. at its centre
• D. only where it was first placed

Explanation: Mutual repulsion drives the charges as far apart as possible, so they collect on the outside, and the surface charge density is highest at…

• A. E equals V times d
• B. E equals V divided by d
• C. E equals d divided by V
• D. E equals V plus d

Explanation: For a uniform field, such as that between parallel plates, the intensity is the potential gradient, so a 100 V supply across plates 2 mm…

• A. increases, because work must be done against their repulsion
• B. decreases
• C. stays constant
• D. becomes negative

Explanation: Like charges repel, so pushing them together requires work and that work is stored as potential energy, which is why the system flies…

• A. a net force but no torque
• B. a torque but no net force
• C. neither force nor torque
• D. both a large net force and a torque

Explanation: The equal and opposite charges feel equal and opposite forces in a uniform field, so the forces cancel, but because they act along…