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Nuclear Force

Nuclear force is the strong attractive force between nucleons that binds protons and neutrons inside the nucleus. It is short-ranged, very strong within nuclear distances, approximately charge-independent, and shows saturation.

In one line: Nuclear force is strong, short, and neighbour-focused.

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Understand it

  • Inside the nucleus, electrostatic repulsion acts between protons, but nuclei remain bound because nuclear force is much stronger at very small separations.
  • The force acts significantly only over a range of a few femtometres.
  • It acts between proton-proton, neutron-neutron, and proton-neutron pairs in nearly the same way, so it is called charge-independent.
  • Its saturation property means each nucleon interacts strongly mainly with nearby nucleons, not equally with all nucleons in a large nucleus.

Example

The deuteron, containing one proton and one neutron, is bound because nuclear force acts attractively between the two nucleons at nuclear separation.

Formula and rule

The useful rule is qualitative: nuclear force is attractive and dominant only at very small nucleon separations, nearly charge-independent, and saturated.

No Class 12 board-level mathematical formula is normally required for this concept.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

Question: Why can a nucleus with many protons remain stable despite proton-proton repulsion?

  1. 1Answer: Protons repel through electrostatic force, but at nuclear separations the strong nuclear force between neighbouring nucleons is much stronger and attractive.
  2. 2Neutrons add nuclear attraction without adding proton-proton repulsion, improving stability in many nuclei.

Method you can reuse

  1. 1State that nuclear force binds nucleons.
  2. 2Mention short range, high strength within the nucleus, charge independence, and saturation.
  3. 3Connect these properties to nuclear binding or stability.
  4. 4Avoid extending the force to atomic or chemical distances.

Visual tip

A small nucleon cluster sketch can show nearest-neighbour interaction to explain saturation. Useful labels: proton, neutron, nearby nucleons, short-range attraction, electrostatic repulsion between protons.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Why does the nuclear force not affect electrons in ordinary atomic orbits?

Think first, then show answer
It does not affect ordinary atomic electrons because nuclear force has a very short range of only a few femtometres, while electrons in atoms are much farther from the nucleus.

Common wrong answer

Neutrons cancel the charge of protons.

Why it loses marks: Neutrons are electrically neutral; they do not cancel proton charge but contribute attractive nuclear force.

Don't mix this up

Students often write that nuclear force acts at atomic distances. It acts only at nuclear distances, roughly of the order of 10−15 m.

Exam tip

In reasoning answers, mention both strength and range. Saying only that nuclear force is strong is incomplete because its short range is equally important.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

This concept is asked in short-answer questions on properties of nuclear force, assertion-reason items comparing nuclear and electrostatic forces, and explanation of why neutrons help nuclear stability.
  1. 1

    Enough for 1 mark

    Nuclear force is the strong attractive force between nucleons that binds protons and neutrons inside the nucleus. It is short-ranged, very strong within nuclear distances, approximately charge-independent, and shows saturation.

  2. 2

    Add for 2 marks

    Example: The deuteron, containing one proton and one neutron, is bound because nuclear force acts attractively between the two nucleons at nuclear separation.

  3. 3

    Add for 3 marks

    Inside the nucleus, electrostatic repulsion acts between protons, but nuclei remain bound because nuclear force is much stronger at very small separations.

Practice

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