Coulomb’s Law

Coulomb’s Law MDCAT MCQs with answers

23 past paper MCQs on Coulomb’s Law, from the Electrostatics unit of MDCAT Physics. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.

Read the notes first Practise the unit as a quiz

1.If we double the separation between two charges, then Coulomb's force will become: (MDCAT 2020)

  1. doubled
  2. half
  3. four times
  4. one fourth
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Correct answer: (d) one fourth

$F\propto1/r^2$, so twice the separation leaves a quarter of the force.

2.Which one of the following statements is true? (MDCAT 2022)

  1. the electrostatic force obeys the inverse square law while the gravitational force does not
  2. both the gravitational force and the electrostatic force are repulsive in nature
  3. the gravitational force is much weaker than the electrostatic force
  4. neither force obeys the inverse square law
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Correct answer: (c) the gravitational force is much weaker than the electrostatic force

Both are inverse square forces, but between two protons gravity is weaker by some $10^{36}$ times.

3.The Coulomb constant depends upon the: (MDCAT 2022)

  1. nature of the medium
  2. system of units
  3. type of charge
  4. nature of the medium and the system of units
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Correct answer: (d) nature of the medium and the system of units

$k=1/4\pi\varepsilon$ carries the permittivity of the medium, and its number depends on the units used.

4.As per Coulomb's law, the force of attraction or repulsion between two point charges is directly proportional to the: (MDCAT 2023)

  1. sum of the magnitudes of the charges
  2. product of the magnitudes of the charges
  3. square of the distance between them
  4. distance between them
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Correct answer: (b) product of the magnitudes of the charges

$F\propto q_1q_2$, and it is inversely proportional to the square of the separation.

5.Coulomb's law states that the force between two point charges is: (MDCAT 2024)

  1. inversely proportional to the product of the charges and directly proportional to the square of the distance between them
  2. directly proportional to the product of the charges and inversely proportional to the square of the distance between them
  3. directly proportional to the sum of the charges and inversely proportional to the square of the distance between them
  4. directly proportional to the product of the charges and to the square of the distance between them
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Correct answer: (b) directly proportional to the product of the charges and inversely proportional to the square of the distance between them

$F=q_1q_2/4\pi\varepsilon_0r^2$.

6.A force of repulsion between two charges is taken as: (UHS MDCAT 2017)

  1. negative
  2. positive
  3. either positive or negative
  4. it cannot be determined
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Correct answer: (b) positive

Coulomb law gives a positive product for like charges, and the positive sign is read as repulsion.

7.If a plastic sheet of relative permittivity 2.5 is inserted between two-point charges placed in vacuum, then the electrostatic force between them: (UHS MDCAT 2025)

  1. Increases by a factor of 2.5
  2. Decreases by a factor of 2.5
  3. Increases by a factor of 5
  4. Decreases by a factor of 5
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Correct answer: (b) Decreases by a factor of 2.5

The medium divides the force by its relative permittivity, so the force falls to $1/2.5$ of its value.

8.If the distance between two charges is halved and magnitude of charges are also doubled, then the force between these charges becomes: (UHS MDCAT 2025)

  1. two times
  2. four times
  3. eight times
  4. sixteen times
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Correct answer: (d) sixteen times

Doubling both charges multiplies the force by four, and halving the separation by four again.

9.Coulomb's law fits well into: (KMU MDCAT 2025)

  1. Newton's 1st law
  2. Newton's 2nd law
  3. Newton's 3rd law
  4. Gauss's law
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Correct answer: (c) Newton's 3rd law

The two charges push or pull each other equally and oppositely, which is the third law.

10.The force between two charges is 28 N in vacuum. If paraffin wax of relative permittivity 2.8 is introduced between the charges as a medium, then the force reduces to: (SIBA MDCAT 2025)

  1. 25 N
  2. 20 N
  3. 15 N
  4. 10 N
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Correct answer: (d) 10 N

The medium divides the force by its relative permittivity, and $28/2.8$ is $10\,\mathrm{N}$.

11.Two equal charges experience a certain force when placed in vacuum. When the charges are placed in a medium, the force becomes 1/4th. The dielectric constant of the medium is: (SZABMU MDCAT 2025)

  1. 0.25
  2. 2
  3. 4
  4. 16
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Correct answer: (c) 4

The medium divides the force by its dielectric constant, so a quarter of the force means a constant of four.

12.The Coulomb's law states (UHS MDCAT 2024)

  1. Force,between two point charges is inversely proportional to the product of the charges and directly proportional to the square of the distance between them
  2. Force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them
  3. Force between two point charges is directly proportional to the sum of the charges and inversely proportional to the square of the distance between them
  4. Force between two point charges is directly proportional to the product of the charges and the square of the distance between them
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Correct answer: (b) Force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them

$F=kq_1q_2/r^2$: proportional to the product of the charges and to the inverse square of the separation.

13.151.Which one of the following Is NOT a feature of electric forces? (UHS MDCAT 2024)

  1. They act on charges
  2. They act on masses
  3. They can be attractive
  4. They can be repulsive
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Correct answer: (b) They act on masses

Electric forces act on charge; it is gravitation that acts on mass.

14.What is the increase in force between two charges if the separation between them is decreased by 50 percent? (KMU MDCAT 2024)

  1. Becomes four times
  2. Doubles
  3. Increases by half
  4. Triples
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Correct answer: (a) Becomes four times

Halving the separation multiplies the inverse square by four.

15.According to Coulomb's law, what happens to the electrostatic force between the 2-point charges if the distance between them is doubled? (KMU MDCAT 2024)

  1. The force becomes one-fourth
  2. The force becomes half
  3. The force doubles
  4. The force remains the same
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Correct answer: (a) The force becomes one-fourth

Doubling the separation leaves a quarter of the force.

16.NaCl dissolves quickly in water due to: (NUMS MDCAT 2024)

  1. Low εr
  2. High εr
  3. εr = 0
  4. εr = ∞
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Correct answer: (b) High εr

Water has a very high relative permittivity, so it weakens the attraction between the ions to about a eightieth.

17.The Coulomb's constant k depends upon: (UHS MDCAT 2023)

  1. nature of medium
  2. system of units
  3. types of charge
  4. nature of medium and system of units
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Correct answer: (d) nature of medium and system of units

$k=1/4\pi\varepsilon$ carries the permittivity of the medium, and its number depends on the units used.

18.The property of material due to which it attracts or repels other objects is: (PMC MDCAT 2022)

  1. Friction
  2. Velocity
  3. Acceleration
  4. Charge
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Correct answer: (d) Charge

That property is electric charge.

19.Which of the following forces are only attractive? (PMC MDCAT 2022)

  1. Electrostatic forces
  2. Gravitational forces
  3. Magnetic forces
  4. Forces between same poles of magnet
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Correct answer: (b) Gravitational forces

Gravitation pulls and never pushes; electric and magnetic forces do both.

20.When two positive charge particles move toward each other In opposite directions: (PMC MDCAT 2022)

  1. repulsion occurs
  2. attraction occurs
  3. Nothing will happen
  4. Charge will be neutralized
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Correct answer: (a) repulsion occurs

Like charges repel, so they push each other apart.

21.Two unlike charges attract each other with a force of 10 N. If the distance between them is doubled, the force between them is: (PMC Practice 2021)

  1. 40 N
  2. 20 N
  3. 5 N
  4. 2.5 N
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Correct answer: (d) 2.5 N

Doubling the separation leaves a quarter of the force, $2.5\,\mathrm{N}$.

22.Charged body attracts uncharged body by ________ induction. (PMC Practice 2021)

  1. Electrostatic
  2. Magnetic
  3. Both A and B
  4. None of these
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Correct answer: (a) Electrostatic

The charged body draws the opposite charge to the near face of the neutral one, which is electrostatic induction.

23.Three objects are brought close to each other, two at a time. When objects A and B are brought together, they repel. When objects B and C are brought together, they also repel. Which of the following is true? (PMC Practice 2021)

  1. Objects A and C possess charges of the same sign, but not B
  2. Objects A and C possess charges of the opposite sign
  3. All three objects possess charges of the same sign
  4. One object is neutral
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Correct answer: (c) All three objects possess charges of the same sign

Only like charges repel, so all three must carry charge of the same sign.

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