Question

Astronomers and physicists need a unit to describe extremely small distances, such as the size of an atomic nucleus. Which unit is commonly used for such tiny lengths, and what is its value in metres?

Hint:

Think of the unit named after Enrico Fermi, used for nuclear scale distances.

Answer 1

Nuclear physics deals with sizes that are almost impossible to picture using ordinary units like the metre or even the nanometre.

To handle this, physicists use the fermi as the standard unit. One fermi equals \(10^{-15}\) metres, which is a million times smaller than a nanometre.

For comparison, an atom as a whole is about \(10^{-10}\) m across, while its nucleus is roughly \(10^{-15}\) m, that is, about a fermi. This huge difference in scale is why nuclear sizes get their own unit instead of being expressed in metres with many zeros after the decimal point.

So the answer is the fermi, equal to \(10^{-15}\) m, also known as the femtometre.