Sci I - Coulomb’s Law

What is the fundamental force of electricity described by?

Coulomb’s law

Who discovered Coulomb’s law and when?

Charles Coulomb in 1785

What apparatus did Coulomb use to measure electric forces?

A torsion balance with a charged rod suspended by a string

What does Coulomb’s law equation FE = k * q1 * q2 / r² represent?

Electric force between two charges

In Coulomb’s law, what do q1 and q2 represent?

The amount of charge on the two objects (in coulombs)

In Coulomb’s law, what does r represent?

The distance between the two charged objects

In Coulomb’s law, what does k represent?

The Coulomb constant

What is the value of the Coulomb constant k?

8.99 × 10⁹ N·m²/C²

What is the charge of a proton?

+1.7 × 10⁻¹⁹ coulombs

What is the charge of an electron?

–1.7 × 10⁻¹⁹ coulombs

Why is the proton/electron charge important?

It is the smallest charge anything can have; charge is quantized

What does quantized charge mean?

Charge comes in discrete, countable amounts

When we talk about static electricity, what charge ranges are typical?

Microcoulombs or nanocoulombs

Why is the fundamental charge so tiny?

Human-scale units are much larger than particle charges; the particles themselves are not "too small"

How is Coulomb’s law similar to gravity?

Both are inverse square laws; FE ∝ charge, FG ∝ mass

What type of forces can electric force be?

Attractive or repulsive

How does gravity differ from electric force in attraction/repulsion?

Gravity is only attractive; electric force can repel or attract

Why is the electric force between two electrons stronger than gravity?

Electric force is ~10⁴⁰ times stronger than gravity

Why don’t we notice electric forces in daily life?

Most atoms have equal numbers of protons and electrons, so most objects are electrically neutral

What happens when you rub a glass rod with cloth?

Glass picks up positive charge, cloth picks up negative charge

Why does the cloth become negatively charged?

It steals electrons from the glass rod

Why is it usually electrons that move in charging?

Electrons are the primary movers of electricity; protons generally stay in place

What happens to total charge when charging occurs?

Charge is conserved; total charge of the system remains zero

What does “charge is conserved” mean?

Charge can’t be created or destroyed, only transferred

What is the total charge of the universe?

Zero