A-Level Physics October/November 2024 Q6(a): Compare an α-particle with a β+ particle in terms of their masses and charges.

1 answer

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  A comparison of the properties of an α-particle and a β+ particle is as follows:

  Mass:

  • The mass of an α-particle is much greater than the mass of a β+ particle. An α-particle has a mass of approximately 4u, while a β+ particle (a positron) has a mass of approximately $5.5 \times 10^{-4}$ u.

  Charge:

  • Both particles are positively charged.
  • The magnitude of the charge on an α-particle is $+2e$, which is twice the magnitude of the charge on a β+ particle ($+1e$).

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  How the marks are awarded

  • B1 — The first mark is awarded for the clear comparative statement that the mass of the α-particle is much greater than that of the β+ particle.
  • B1 — The second mark is awarded for identifying the similarity in the sign of their charge, stating that both particles are positively charged.
  • B1 — The third mark is awarded for correctly comparing the magnitudes of the charges, stating that the α-particle's charge is twice that of the β+ particle.

  Common mistakes

  • Stating that the β+ particle is negatively charged, confusing it with a β- particle (an electron).
  • Incorrectly stating the charge ratio, for example, saying the α-particle charge is four times greater (confusing nucleon number with charge number).
  • Simply listing the properties of each particle (e.g., mass in u, charge in C) without making an explicit comparative statement like 'much greater' or 'twice'.
  • Stating that one particle is charged and the other is not, or that they have opposite charges.

  Examiner tip: When a question asks you to 'compare' two items, ensure your answer uses explicit comparative language (e.g., 'greater than', 'twice', 'the same as') for each property, rather than just listing individual facts.

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