OCR · A-Level · Physics
Course version: H556 · Version from Sept 2015
(e) strong nuclear force; short-range nature of the force; attractive to…
Full specification wording
The nuclear atom: (e) strong nuclear force; short-range nature of the force; attractive to about 3 fm and repulsive below about 0.5 fm
The strong nuclear force acts between nucleons and holds the nucleus together against electrostatic repulsion between protons.
Checked against the OCR H556 specification (opens in a new tab) on .
- Point 5 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
The strong nuclear force acts between nucleons and holds the nucleus together against electrostatic repulsion between protons. It is much stronger than the electrostatic force at nuclear separations but is short-range. Its behaviour depends on the separation between nucleons: at distances greater than about 3 fm it is negligible; between about 0.5 fm and 3 fm it is attractive, with a maximum attraction around 1 fm; below about 0.5 fm it becomes repulsive, preventing nucleons from collapsing into each other. This short-range attraction explains why large nuclei need more neutrons for stability, because the strong force only acts between neighbouring nucleons while electrostatic repulsion acts throughout the nucleus.
What earns the marks
- The strong nuclear force acts between nucleons and is responsible for holding the nucleus together.
- The strong force is much stronger than the electrostatic repulsion between protons at nuclear distances.
- The short-range nature means only neighbouring nucleons interact strongly, which affects nuclear stability.
Common mistakes and how to put them right
Thinking the strong force acts over unlimited distance.
Put it right: It is short-range and negligible beyond about 3 fm.
Believing the strong force is always attractive.
Put it right: It becomes repulsive below about 0.5 fm.
Confusing the strong force with the electrostatic force.
Put it right: The strong force acts between all nucleons, while electrostatic repulsion acts only between protons.
Assuming the strong force acts between protons only.
Put it right: It acts between protons and neutrons and between neutrons themselves.
Exam tips
- Memorise the approximate distances: attractive up to about 3 fm, repulsive below about 0.5 fm.
- When comparing forces, state that the strong force is much stronger than electrostatic repulsion at nuclear separations.
- Use the short-range nature to explain why neutrons are needed for stability in larger nuclei.
Try the lesson
The start of the The nuclear atom: (e) strong nuclear force; short-range nature of the force; attractive to about 3 fm and repulsive below about 0.5 fm lesson, made from checked teaching notes for this specification point.
Listen
The strong nuclear force acts between nucleons and holds the nucleus together against electrostatic repulsion between protons. It is much stronger than the electrostatic force at nuclear separations but is short-range. Its behaviour depends on the separation between nucleons: at distances greater than about 3 fm it is negligible; between about 0.5 fm and 3 fm it is attractive, with a maximum attraction around 1 fm; below about 0.5 fm it becomes repulsive, preventing nucleons from collapsing into each other. This short-range attraction explains why large nuclei need more neutrons for stability, because the strong force only acts between neighbouring nucleons while electrostatic repulsion acts throughout the nucleus. A strong answer earns marks for these points. The strong nuclear force acts between nucleons and is responsible for holding the nucleus together. The strong force is much stronger than the electrostatic repulsion between protons at nuclear distances. The short-range nature means only neighbouring nucleons interact strongly, which affects nuclear stability. Exam tip: Memorise the approximate distances: attractive up to about 3 fm, repulsive below about 0.5 fm.
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Key words
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Strong nuclear force
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Short-range interactions
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Nuclear stability
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Force-separation relationship
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See every definition
- Strong nuclear force
- Acts between nucleons and holds the nucleus together against electrostatic repulsion between protons, being much stronger than the electrostatic force at nuclear separations.
- Short-range interactions
- The force is short-range, becoming negligible beyond about 3 fm, so only neighbouring nucleons interact strongly.
- Nuclear stability
- The short-range attraction explains why large nuclei need more neutrons for stability, because the strong force only acts between neighbouring nucleons while electrostatic repulsion acts throughout the nucleus.
- Force-separation relationship
- Between about 0.5 fm and 3 fm the force is attractive, with a maximum attraction around 1 fm, and below about 0.5 fm it becomes repulsive, preventing nucleons from collapsing into each other.
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