E.3.14 (HL)—Evidence for strong force

Use nuclear stability as evidence

Protons repel electrically, yet stable nuclei exist. This requires an additional attractive interaction between nucleons that is strong enough at nuclear distances.

Use scattering evidence

At high energies, deviations from Rutherford scattering show that the electrostatic model is incomplete at close range. The change is evidence for the strong interaction becoming relevant.

State the evidence precisely

Evidence supports a short-range strong force; it does not by itself provide a complete potential-energy curve or a long-range attraction between nuclei.

Common trap

Do not use “the nucleus is stable” as a complete explanation. State which observed fact requires an attractive force and how its range differs from electromagnetic repulsion.

How it is assessed

Questions ask for one piece of evidence and an explanation, sometimes alongside conservation-law analysis.

Command terms

State / Explain

What earns marks

Link proton repulsion or Rutherford deviation to an attractive short-range strong interaction; avoid unsupported claims about other forces.

Watch for

Naming the force without explaining the evidence or confusing strong-force evidence with conservation-law violations.

Retrieve the HL evidence

Nuclear stability, scattering deviations, the N–Z stability band and discrete alpha/gamma spectra reveal the strong interaction and quantized nuclear levels.

Retrieve the decay equations

Use $N=N_0e^{-\lambda t}$ , $A=\lambda N$ , and $T_{1/2}=\ln2/\lambda$ . The continuous beta spectrum is explained by neutrino energy sharing.

E.3.14 (HL)—Evidence for strong force

Use Evidence for Strong Force

E.3.14 (HL) Exam Analysis

Assessment in practice

Retrieve the HL Nuclear Model