A Level Physics Practice Exam

Why is the charge of a proton positive?

1. It has more neutrons than protons

2. The sum of its quark's charges is 1

3. It contains only positive quarks

4. It is formed by electrons

The correct answer is: The sum of its quark's charges is 1

The charge of a proton is defined as positive due to the intrinsic properties of its constituent particles, specifically its quarks. A proton is composed of three quarks: two up quarks and one down quark. The up quark carries a charge of +2/3, while the down quark has a charge of -1/3. When calculating the total charge of the proton, the charges of the quarks are summed up: (2/3) + (2/3) - (1/3) = 1. This total charge of +1 is designated as positive, and thus the proton itself is considered to have a positive charge. The definition of charge as positive in this context is based on convention established in physics, where a proton is assigned a positive charge and an electron a negative charge. Understanding the behavior of quarks within particles like protons provides insight into the nature of charge itself and the fundamental forces at play in atomic structure. The concept of charge is defined by these particles' intrinsic properties rather than any external or arbitrary assignment.