O Levels Physics (5054)•5054/12/M/J/19
Explanation
Alpha Particle Composition Steps:
- An alpha particle is a helium-4 nucleus consisting of 2 protons and 2 neutrons.
- Each proton has charge +q and mass m; each neutron has charge 0 and mass m.
- Total charge = 2(+q) + 2(0) = 2q.
- Total mass = 2m + 2m = 4m.
Why B is correct:
- It matches the standard nuclear composition: charge from 2 protons, mass from 2 protons + 2 neutrons.
Why the others are wrong:
- A: Charge correct, but mass underestimates neutrons.
- C: Charge doubles protons incorrectly; mass ignores neutrons.
- D: Charge doubles protons incorrectly; mass correct but charge wrong.
Final answer: B
Topic: The nucleus
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