Consider the forces between two protons separated by a distance of the order of 1 femtometre (10⁻¹⁵ m). The correct order of the strengths of the electromagnetic, gravitational and nuclear forces acting between them is:

Correct answer: (d) Nuclear > Electromagnetic > Gravitational

Explanation

At a distance of about 1 femtometre (the size of a nucleus), the forces between two protons compare as:

• nuclear (strong) force: the strongest; it holds protons and neutrons together in the nucleus, but acts only over about 10⁻¹⁵ m;
• electromagnetic force: the repulsion between the two positive charges; strong, but about 100 times weaker than the nuclear force at this distance;
• gravitational force: far weaker than both, about 10⁻³⁶ times the electromagnetic force between two protons.

So nuclear > electromagnetic > gravitational.