Quantisation of charge

Beginner

Charge comes in multiples of e.

Key relationq = ne, e=1.6×10⁻¹⁹ C

Free charge occurs only in integer multiples of e = 1.602×10⁻¹⁹ C (quarks carry e/3 but are not seen alone). Millikan's experiment showed this.

Worked example

1 C is about 6.24×10¹⁸ electrons.

Common mistake

At everyday scales it looks continuous.

In more detail

Electric charge is quantised: every charge is an integer multiple of the elementary charge, e = 1.6 × 10⁻¹⁹ C. The electron has charge −e.

Atomic and nuclear physics use the elementary charge in calculations.
Single-electron transistors exploit charge quantisation.
Physicists note that the charge on an electron, 1.6 × 10⁻¹⁹ coulombs, is the smallest unit of electric charge.

Are quarks an exception?

Quarks carry fractional charges, but they are never found alone, so free charges remain integer multiples of e.

How small is e?

Very small, about one sixth of a billionth of a billionth of a coulomb.

Why is the elementary charge important?

All charges in nature are whole-number multiples of it, which is why charge is said to be quantised.