A Levels Physics (9702)•9702/12/M/J/23
Explanation
Meson charge from quark-antiquark pair
Steps:
- Mesons consist of one quark and one antiquark.
- Up quark has charge +2/3 e.
- For total charge +e, the antiquark must contribute +1/3 e.
- Anti-down quark has charge +1/3 e, as down quark is -1/3 e.
Why A is correct:
- Up (+2/3 e) and anti-down (+1/3 e) sum to +e, matching the meson's charge.
Why the others are wrong:
- B: Anti-up has -2/3 e; total with up is 0.
- C: Bottom has -1/3 e; total with up is +1/3 e.
- D: Charm has +2/3 e; total with up is +4/3 e.
Final answer: A
Topic: Fundamental particles
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