A Level Physics Practice Exam

When does the strong nuclear force become effective?

1. Beyond 4fm

2. At distances less than 0.5fm

3. Between 0.5fm and 4fm

4. Only at zero distance

The correct answer is: Between 0.5fm and 4fm

The strong nuclear force becomes effective in the range of approximately 0.5 femtometers (fm) to about 4 femtometers. Within this distance, the force is primarily responsible for holding protons and neutrons together in the atomic nucleus. At distances less than 0.5 fm, the strong force can become extraordinarily strong, but the scale at which it is typically considered effective starts just above that. As the distance grows beyond 4 fm, the strong nuclear force significantly weakens and is not sufficient to overcome the electromagnetic repulsion between protons, which is why nuclear stability is compromised at larger distances. Thus, the range from 0.5 fm to 4 fm is crucial, as it marks the effective operational distance of the strong force, where it can best counteract the repulsive forces and maintain the integrity of the nucleus. This understanding is foundational in nuclear physics, highlighting how the strong force operates at very short ranges to create stable atomic structures.