Equations · Physics
Coulomb's law
The electric force between two point charges, falling with the square of the distance.
F = (1 / (4πε₀)) q₁q₂ / r²
Aethel says
F equals the quantity 1 over the quantity 4 pi epsilon naught, times q sub one q sub two over r squared
What it says
Like charges repel and opposite charges attract. The force is proportional to the product of the charges and inversely proportional to the square of the distance, the same shape as Newton's law of gravitation.
The constant in front is about 8.988 × 10⁹ N·m²/C², often written k.
Symbol by symbol
| Symbol | Say it | Means |
|---|---|---|
| ε₀ | epsilon naught | the permittivity of free space, about 8.854 × 10⁻¹² F/m |
| q₁, q₂ | q sub one, q sub two | the two charges, in coulombs |
| r | r | the distance between the charges |
Where you meet it
Electromagnetism and chemistry.
Questions
How do you say Coulomb's law out loud?
F = (1 / (4πε₀)) q₁q₂ / r² is read: “F equals the quantity 1 over the quantity 4 pi epsilon naught, times q sub one q sub two over r squared.” That is exactly what Aethel says when it meets the formula in a book.
What does ε₀ mean in Coulomb's law?
ε₀ (said “epsilon naught”) is the permittivity of free space, about 8.854 × 10⁻¹² F/m.
What does q₁, q₂ mean in Coulomb's law?
q₁, q₂ (said “q sub one, q sub two”) is the two charges, in coulombs.
Can I listen to the equations in my own textbook like this?
Yes. Upload a PDF, EPUB or text file and Aethel reads it aloud with every equation spoken as maths, the way it reads this one, and highlights each sentence as it goes. You can start free.