Coulomb's Law Physics Example 1

Follow the full solution, then compare it with the other examples linked below.

Example 1

medium
Two charges q1=3×10−6 Cq_1 = 3 \times 10^{-6} \text{ C} and q2=5×10−6 Cq_2 = 5 \times 10^{-6} \text{ C} are separated by 0.2 m0.2 \text{ m}. What is the electrostatic force between them? Use k=9×109 N m2/C2k = 9 \times 10^9 \text{ N m}^2/\text{C}^2.

Solution

  1. 1
    Apply Coulomb's law: F=k∣q1q2∣r2F = k\frac{|q_1 q_2|}{r^2}
  2. 2
    F=9×109×3×10−6×5×10−6(0.2)2F = 9 \times 10^9 \times \frac{3 \times 10^{-6} \times 5 \times 10^{-6}}{(0.2)^2}
  3. 3
    F=9×109×15×10−120.04=9×109×3.75×10−10=3.375 NF = 9 \times 10^9 \times \frac{15 \times 10^{-12}}{0.04} = 9 \times 10^9 \times 3.75 \times 10^{-10} = 3.375 \text{ N}

Answer

F=3.375 NF = 3.375 \text{ N}
Coulomb's law describes the electrostatic force between two point charges. Like gravity, it follows an inverse-square law, but it can be attractive or repulsive depending on the signs of the charges.

About Coulomb's Law

Coulomb's law gives the electric force between two point charges. The force gets larger when the charges are larger and gets smaller with the square.

Learn more about Coulomb's Law →

More Coulomb's Law Examples

Example 2 hard

Two identical charges experience a force of [formula] when separated by [formula]. What is the magni

Example 3 medium

If the distance between two charges is tripled, by what factor does the electrostatic force change?

Example 4 hard

Two charges [formula] and [formula] are separated by [formula]. (a) Calculate the force between them

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