Coulomb’s Law and Electric Field Intensity Fundamentals Quiz Quiz

Explore essential principles of Coulomb’s Law and electric field intensity with this quiz designed to test your understanding of charge interactions and field calculations. Assess your grasp on force calculations, vector considerations, and unit analysis in classical electrostatics.

1. Calculating Electric Force Between Charges

   If two point charges of +2 microcoulombs and -3 microcoulombs are placed 0.5 meters apart in a vacuum, which of the following determines the magnitude of the force between them according to Coulomb’s Law?

   1. F = k |q1 q2| / r^2
   2. F = k |q1 + q2| / r
   3. F = k q1^2 / r^2
   4. F = q1 q2 / (4πε0 r^2)

   Explanation: The correct formula for the magnitude of force between two point charges is F = k |q1 q2| / r^2, where k is Coulomb’s constant. The option with (q1 + q2) describes a sum, not the interaction, and does not fit Coulomb’s Law. The formula with q1 q2 divided by 4πε0 r^2 is similar but k is defined as 1/(4πε0), so it is just another representation. The option with q1 squared doesn’t account for both charges and is incorrect.

2. Vector Nature of Electric Force

   What is the direction of the electric force experienced by a positive test charge placed near a stationary negative point charge?

   1. The force is attractive and points toward the negative charge.
   2. The force is repulsive and points away from the negative charge.
   3. The force acts perpendicular to the line joining the charges.
   4. The force only exists if both charges are positive.

   Explanation: A positive and a negative charge attract each other, so the force on the positive test charge will always be toward the negative charge, making this correct. If it were repulsive, it would point away, which applies only if both charges are of the same sign. Perpendicular force directions are not applicable here as Coulomb’s law force acts along the line joining the charges. The force does not require both charges to be positive.

3. Electric Field Intensity at a Point

   What is the correct expression for the electric field intensity (E) at a distance r from a point charge Q in vacuum?

   1. E = k Q / r
   2. E = k Q^2 / r^2
   3. E = k |Q| / r^2
   4. E = Q / (4πε0 r)

   Explanation: The electric field intensity produced by a point charge at distance r is given by E = k |Q| / r^2. The option with r in the denominator without squaring is incorrect; electric field decays with the square of the distance. The Q squared option is valid for force between two charges, not field calculation. Dividing by 4πε0 r is not the correct expression unless rearranged for k; however, it misses r squared.

4. Units of Electric Field Intensity

   Which of the following is the correct SI unit for electric field intensity?

   1. Joule per coulomb
   2. Coulomb per meter
   3. Volt per ampere
   4. Newton per coulomb

   Explanation: Electric field intensity is measured in newtons per coulomb, representing the force experienced per unit charge. Volt per ampere is the unit for resistance. Coulomb per meter is not a standard unit in this context. Joule per coulomb is equivalent to volts, which measures potential, not electric field.

5. Effect of Distance on Electric Force

   If the separation between two point charges is doubled, how does the magnitude of the electrostatic force between them change?

   1. It becomes one-fourth its original value.
   2. It doubles.
   3. It decreases by half.
   4. It remains unchanged.

   Explanation: Coulomb’s Law states that the force is inversely proportional to the square of the distance; doubling the distance causes the force to fall to one-fourth its original value. Doubling, no change, or halving don’t reflect the inverse square relationship and thus are incorrect. Remember, small changes in distance can significantly affect the force due to the square.