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Chapter 8 Practice Paper: Radioactivity — question paper

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QQ/S4CPH/CH8

Secondary 4 · Combined Science (Physics) (G2 / G3)

Chapter 8 Practice Paper

Radioactivity

Duration: 40 minutes
Total: 30 marks
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Class:
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Date:

READ THESE INSTRUCTIONS FIRST

  • Answer all questions.
  • Section A: choose the one correct answer for each multiple-choice question.
  • Section B: answer in the spaces provided; show all necessary working.
  • Give numerical answers to 3 significant figures where appropriate, with units.
  • The acceleration of free fall near the Earth is 10 m/s².
  • The speed of sound in air is 340 m/s unless stated otherwise.
  • The use of a calculator is permitted.

Original practice material written for the MOE Combined Science (Physics) syllabus. It is not an official MOE or school examination paper. Chapter 8 (nucleus of protons and neutrons with electrons; proton number, nucleon number, isotopes, nuclide notation; random spontaneous decay; alpha, beta and gamma — ionising effect and penetrating power; background radiation; half-life from tables and curves; applications and hazards).

For Examiner’s Use
Section A/ 10
Section B/ 20
Total/ 30

Section A: Multiple-choice questions[10 marks]

Choose the one correct answer for each question.

  1. 1

    An atom’s mass is concentrated in

    1. Athe nucleus of protons and neutrons
    2. Bthe electron shells
    3. Cits electromagnetic waves
    4. Dan even spread across the atom
    ( )
  2. 2

    Isotopes of an element have

    1. Athe same number of neutrons but different protons
    2. Bthe same number of protons but different numbers of neutrons
    3. Cno electrons
    4. Ddifferent chemical symbols
    ( )
  3. 3

    Which radiation is stopped by a few millimetres of aluminium?

    1. Aalpha
    2. Bgamma
    3. Cbeta
    4. Dall three equally
    ( )
  4. 4

    A counter reads 42 counts/min with no source nearby. The 42 counts/min is

    1. Athe source’s activity
    2. Ba fault in the counter
    3. Cthe half-life
    4. Dbackground radiation
    ( )
  5. 5

    A source’s activity falls from 480 counts/min to 240 counts/min in 5.0 minutes. Its half-life is

    1. A2.5 minutes
    2. B5.0 minutes
    3. C10 minutes
    4. D480 minutes
    ( )

Section B: Structured questions[20 marks]

Answer all questions in the spaces provided. Show all necessary working.

  1. 1

    The nuclide notation for a carbon-14 atom is written with a nucleon number of 14 and a proton number of 6.

    1. (a)

      State the numbers of protons, neutrons and electrons in a neutral carbon-14 atom.

      [3]
    2. (b)

      Carbon-12 has the same proton number but a nucleon number of 12. Explain why carbon-12 and carbon-14 are isotopes.

      [2]
    3. (c)

      State what occupies most of the atom’s volume, and where nearly all its mass sits.

      [1]
  2. 2

    The activity of a source is measured every 5 minutes and corrected for background radiation: 480, 240, 120, 60 counts/min at 0, 5, 10, 15 minutes.

    1. (a)

      State what "corrected for background radiation" means, and why it is done.

      [2]
    2. (b)

      Determine the half-life of the source.

      half-life =min[2]
    3. (c)

      Predict the corrected activity at 20 minutes and at 25 minutes.

      activity =counts/min[3]
  3. 3

    Alpha, beta and gamma radiations from a sample are aimed at a sheet of paper, an aluminium sheet and a thick lead block in turn.

    1. (a)

      State which radiation(s) pass through (i) the paper, (ii) the aluminium, (iii) the lead.

      [3]
    2. (b)

      State the nature of alpha radiation, and rank the three radiations by ionising effect.

      [2]
    3. (c)

      State one hazard of over-exposure to these radiations and one precaution.

      [2]

— End of paper —