9702 · 18.3
Electric force between point charges
Have you ever felt a small shock from static electricity, perhaps after walking on carpet? This everyday phenomenon is a demonstration of **electrostatic force**. In Cambridge Physics, we learn to precisely quantify this invisible push or pull between tiny charged particles using a fundamental principle called **Coulomb's Law**. This law helps us predict both the strength and nature of these electric interactions. This pilot aligns with **Senpai Corner** A Level notes (2025-2027) for topic **18.3**.
Need to know
What you need to know
- The electrostatic force is directly proportional to the product of the magnitudes of the charges ($F \propto Q_1 Q_2$).
- The force is inversely proportional to the square of the distance separating the charges ($F \propto 1/r^2$).
- Charges of the same sign (both positive or both negative) result in a repulsive force.
- Charges of opposite signs (one positive and one negative) result in an attractive force.
- For practical calculations, the permittivity of air is typically assumed to be the same as a vacuum.
Explanation
Electric force between point charges
- The electrostatic force is directly proportional to the product of the magnitudes of the charges ($F \propto Q_1 Q_2$).
- The force is inversely proportional to the square of the distance separating the charges ($F \propto 1/r^2$).
- Charges of the same sign (both positive or both negative) result in a repulsive force.
- Charges of opposite signs (one positive and one negative) result in an attractive force.