A Level Physics Practice Exam

What defines the charge of a pion?

1. The absence of down quarks

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

3. The presence of only positive quarks

4. A balance between protons and neutrons

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

The charge of a pion is determined by the sum of the charges of its constituent quarks. Pions are mesons composed of a quark and an antiquark. For example, a positively charged pion (π⁺) consists of an up quark (charge +2/3) and a down antiquark (charge +1/3), resulting in a total charge of +1. Likewise, a negatively charged pion (π⁻) is made up of a down quark and an up antiquark, yielding a total charge of -1. Thus, the overall charge of a pion is fundamentally linked to the combination of the quark charges, which when added together, equate to 1 for the positively charged pion and -1 for the negatively charged one. The neutral pion (π⁰) has a different configuration, but its charge is still defined by the sum of its quark contributions, which equals 0. This understanding clarifies the fundamental nature of how pions obtain their electronic charge, highlighting the significance of quark combinations in determining particle properties.