ICSE Class 9 Answered

Until 20 years ago, it was believed that the smallest particles making up the atoms were protons and neutrons. Yet, most recently, it has been discovered that there are much smaller particles in the atom that form the abovementioned particles.

This discovery led to the development of a branch of physics called "Particle Physics" investigating the "sub-particles" within the atom and their particular movements. Research conducted by particle physics revealed that the protons and neutrons making up the atom are actually formed of sub-particles called "quarks".

The dimension of the quarks that form the proton, which is so small as to exceed the capabilities of human imagination, is much more astounding: 10-18 (0.000000000000000001) metres.