State the properties of the nuclear force. Draw a graph showing how the potential energy of a pair of nucleons varies with their separation, and explain it.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Define the force. The nuclear force is the strong attractive force between nucleons that holds the nucleus together.
2 · List the properties.
Strongest of all forces
Short range: a few fm
Charge independent
Saturates: acts only between nearest neighbours
3 · Draw the graph. [Graph: potential energy (MeV) against r (fm); high at small r, deep minimum at r₀ ≈ 0.8 fm, rising to zero by about 3 fm]
4 · Explain the graph. Below r₀ the force is strongly repulsive; between r₀ and a few fm it is attractive; beyond that it is almost zero.
5 · Real life. This force holds together the nucleus of every atom in our bodies and food.
6 · Close in one line. So, the nuclear force is strong, short range and the same for all nucleon pairs.
Scoring tip: Mark r₀ = 0.8 fm on the x-axis and write 'attractive' and 'repulsive' on the correct sides of it.
