In particle physics, the charge on a positron is equal in magnitude and sign to the charge on which of the following particles?

Introduction / Context:
This question tests your knowledge of elementary particles and their electric charges. A positron is the antiparticle of the electron and plays an important role in nuclear decay processes and medical imaging techniques such as positron emission tomography. Understanding how its charge compares with that of familiar particles like the proton helps clarify basic charge relationships.

Given Data / Assumptions:
- The particle under consideration is the positron, often denoted e+.
- Options include proton, electron, alpha particle and neutron.
- We focus on the magnitude and sign of the electric charge on each particle.

Concept / Approach:
The positron is defined as the antimatter counterpart of the electron. It has the same mass as an electron but the opposite electric charge. The electron has a charge of -1 in elementary charge units, whereas the positron has a charge of +1. The proton also has a charge of +1 in the same units. An alpha particle (a helium nucleus) has a charge of +2, and a neutron has zero charge. Therefore, in terms of magnitude and sign, the charge on a positron matches the charge on a proton.

Step-by-Step Solution:
Step 1: Recall that the electron has a charge of -1 (negative elementary charge). Step 2: As the antiparticle of the electron, the positron has the same mass as the electron but a charge of +1. Step 3: A proton, the positively charged particle in the nucleus, also has a charge of +1. Step 4: An alpha particle, being a helium nucleus containing two protons and two neutrons, has a total charge of +2. Step 5: A neutron has no net charge; its charge is 0. Step 6: Therefore, the positron and proton share the same charge magnitude and sign, making proton the correct answer.

Verification / Alternative check:
Charge conservation in nuclear reactions provides an additional check. In beta plus decay, a proton in the nucleus converts into a neutron and emits a positron and a neutrino. The proton (charge +1) changes to a neutron (charge 0) plus a positron (charge +1), so the total charge before and after remains +1. This reaction would not balance correctly if the positron had any charge other than +1. Since the proton also has +1, this confirms that their charges are equal in magnitude and sign.

Why Other Options Are Wrong:
Electron: Has a charge of -1, opposite in sign to the positron, which is +1.
Alpha particle: Has a charge of +2, double the charge of a positron; therefore, they are not equal.
Neutron: Has zero charge, so its charge cannot equal the non zero charge of a positron.

Common Pitfalls:
A common confusion is to think that a positron must have the same charge as an alpha particle because both are positive. However, it is essential to compare numerical values, not just the sign. Another pitfall is to assume that the positron, as a type of electron, must have a small or fractional charge. In fact, all these particles carry integer multiples of the elementary charge. Remember that a positron and a proton both carry a single positive elementary charge, +1.

Final Answer:
The charge on a positron is equal to the charge on a proton.