Question

Which graph in the following diagram correctly represents the potential energy of a pair of nucleons as a function of their separation?

• A.
• B.
• C.
• D.

Answer 1

The Correct Option is D

• Repels strongly at small separations (r < 0.5 fm) → high positive U.
• Attracts at intermediate distances (0.5 fm < r < 2 fm) → negative U.
• Drops to zero for r > 2 fm.

Why D? Only option D uses correct units (U in MeV, r in fm) and matches this behavior.

Others fail because:

• B, C: Wrong units (r in meters, U in keV).
• A: Undefined graph shape (if drawn correctly, could also be valid).

The correct answer is (D) : .

Answer 2

In nuclear physics, the potential energy of a pair of nucleons (such as protons or neutrons) typically follows a shape where: 

- At very large separations, the potential energy is nearly zero. 
- As the nucleons move closer, the potential energy decreases (becomes negative) due to the attractive nuclear force. 
- After reaching a minimum, the potential energy increases rapidly at very short distances due to repulsive forces (this is often due to the Pauli exclusion principle for fermions or the electrostatic repulsion between protons). 

Graph (D) correctly represents this behavior, showing a sharp attractive region at intermediate distances and a repulsive region at very short distances, which is characteristic of the nuclear force.

The correct answer is (D) : .