Coulomb's Law and Superposition
Two point charges exert a force F = k q1 q2/r2 along the line joining them, with k = 1/(4 π e0).
What is Coulomb's Law and Superposition?
Two point charges exert a force F = k q1 q2/r2 along the line joining them, with k = 1/(4 π e0).
Key formula / rule: F = q1 q2/(4 π e0 r2); e0 = 8.85 x 10-12 C2/N m2.
Key points
- Apply Coulomb's law with superposition to charge systems.
- Compare electrostatic and gravitational forces.
Common exam trap
Adding forces as scalars in multi-charge problems.
Definitions
- Term
Coulomb's Law and Superposition
- Meaning
Two point charges exert a force F = k q1 q2/r2 along the line joining them, with k = 1/(4 π e0).
- Term
Coulomb's Law and Superposition — explanation
- Meaning
Coulomb's law shares the inverse-square form with gravitation but can be attractive or repulsive, and is enormously stronger. Forces from several charges add vectorially, one pair at a time.
Learning objectives
Apply Coulomb's law with superposition to charge systems.
Compare electrostatic and gravitational forces.
Formulae
- Key point
F = q1 q2/(4 π e0 r2); e0 = 8.85 x 10-12 C2/N m2.
- Key point
The force is reduced by a factor K in a dielectric medium.
- Key point
Superposition: total force is the vector sum of pairwise forces.
Prerequisites
PHY-U1-KIN-T2-S1-C1
Common mistakes
Adding forces as scalars in multi-charge problems.
Forgetting the dielectric constant of the medium.
Keywords
Coulomb
Superposition
Practice preview
Two point charges, one positive and one negative, are placed a certain distance apart. What is the nature of the electrostatic force between them?…
easy
Two point charges, +2 microC and +3 microC, are placed 30 cm apart in vacuum. Calculate the magnitude of the electrostatic force between them. (Given: k = 9 x 10^9 N m^2 C^-2)…
easy
Three point charges, q1 = +1 microC, q2 = -2 microC, and q3 = +3 microC, are placed along a straight line. q1 is at x=0, q2 is at x=1m, and q3 is at x=2m. What is the net electrostatic force on q2? (Given: k = 9 x 10^9 N…
medium