Coulomb's law (A-level only) Flashcards – AQA A-level Physics (7408)

What is Coulomb’s law for the magnitude of the force between two point charges in a vacuum?

$F=\frac{1}{4\pi\varepsilon_0}\frac{|Q_1Q_2|}{r^2}$ Here $Q_1$ and $Q_2$ are the charges, $r$ is their separation, and $\varepsilon_0$ is the permittivity of free space.

Along what line does the electrostatic force between two point charges act?

Along the line joining the charges.

How does the electrostatic interaction differ for like and unlike charges?

Like charges repel; unlike charges attract.

How can air be treated when calculating the electrostatic force using Coulomb’s law?

As a vacuum.

How can a spherically symmetric charged sphere be treated when calculating its force on a charge outside it?

Its charge can be treated as concentrated at its centre.

What is the gravitational force magnitude between two point particles of masses $m_1$ and $m_2$ separated by $r$?

$F_g=\frac{Gm_1m_2}{r^2}$

What is the electrostatic force magnitude between two point particles with charges $Q_1$ and $Q_2$ separated by $r$?

$F_e=\frac{|Q_1Q_2|}{4\pi\varepsilon_0r^2}$

What is the ratio of electrostatic to gravitational force magnitudes between two charged point particles?

$\frac{F_e}{F_g}=\frac{|Q_1Q_2|}{4\pi\varepsilon_0Gm_1m_2}$

Why is the ratio of electrostatic to gravitational force independent of the particles’ separation?

Both forces follow an inverse-square law, so the separation factors cancel.

How do the magnitudes of electrostatic and gravitational forces typically compare between charged subatomic particles?

The electrostatic force is typically much greater than the gravitational force.

How do gravity and electrostatic force differ in whether they attract or repel particles?

Gravity is attractive; electrostatic force can be attractive or repulsive, depending on the charge signs.