Cambridge International AS & A Level · 11 · structured
Infer the nuclear atom and compare radiation energies
Infer the nuclear atom and compare radiation energies · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- demanding
- Marks
- 16
- Topics
- 6
- Answer
- Complete
In a thin-foil alpha-scattering experiment, most alpha particles pass through with little change of direction, some are deflected and very few turn through large angles. Consider neutral atoms ²⁰₁₀Ne and ²²₁₀Ne. Use 1u=1.66×10⁻²⁷kg. The force on a positively charged alpha particle near the atomic centre is repulsive.
- (a)
Use each of the stated scattering observations to infer the size, charge and concentration of atomic mass. Explain why a diffuse positive-charge model is inadequate.
4 marks - (b)
Describe the nuclear-atom model and find proton, neutron and electron counts for both neutral neon atoms. Define isotopes using this pair.
4 marks - (c)
Contrast alpha-particle and beta-particle energy spectra for a specified decay and explain the role of the (anti)neutrino in the beta spectrum.
3 marks - (d)
A nucleus has mass55.9u. Convert to kilograms. Another has mass3.32×10⁻²⁶kg. Convert to u and state why u is a mass unit, not an energy unit.
3 marks - (e)
Identify the electron's antiparticle and compare their rest masses and electric charges. Does equal mass imply equal charge?
2 marks
Ready to self-mark?Reveal the detailed answer guide
(a)
Use each of the stated scattering observations to infer the size, charge and concentration of atomic mass. Explain why a diffuse positive-charge model is inadequate.
Identify what the question is testing, organise the response into distinct mark-earning points, and make every conclusion traceable to a physical principle or to the evidence supplied.
- 1
Connect majority small deflection to nucleus much smaller than atom.
- 2
Connect positive-alpha repulsion to positive nuclear charge.
- 3
Connect rare large angles to concentration of mass and charge.
- 4
Reject diffuse positive charge using inadequate strong localized force.
(b)
Describe the nuclear-atom model and find proton, neutron and electron counts for both neutral neon atoms. Define isotopes using this pair.
List the given quantities with units, identify the required quantity, write the governing relationship before substituting, and keep extra digits until the final line so rounding does not distort the result.
- 1
Place protons and neutrons in nucleus; electrons outside.
- 2
UseZ=10 for both protons and neutral electrons.
- 3
UseN=A−Z for10 and12.
- 4
Define same element/Z with differentN.
(c)
Contrast alpha-particle and beta-particle energy spectra for a specified decay and explain the role of the (anti)neutrino in the beta spectrum.
Identify what the question is testing, organise the response into distinct mark-earning points, and make every conclusion traceable to a physical principle or to the evidence supplied.
- 1
State discrete rather than one universal alpha energy for all nuclides.
- 2
State continuous beta distribution.
- 3
Explain variable sharing with a neutral lepton, not different electron rest masses.
(d)
A nucleus has mass55.9u. Convert to kilograms. Another has mass3.32×10⁻²⁶kg. Convert to u and state why u is a mass unit, not an energy unit.
List the given quantities with units, identify the required quantity, write the governing relationship before substituting, and keep extra digits until the final line so rounding does not distort the result.
- 1
Multiply 55.9 by 1.66×10⁻²⁷.
- 2
Divide 3.32×10⁻²⁶ by 1.66×10⁻²⁷.
- 3
Keep dimensions mass; do not report mass in joules.
(e)
Identify the electron's antiparticle and compare their rest masses and electric charges. Does equal mass imply equal charge?
Identify what the question is testing, organise the response into distinct mark-earning points, and make every conclusion traceable to a physical principle or to the evidence supplied.
- 1
Name positron and mass equality.
- 2
Give equal charge magnitudes with opposite signs.
Complete marking guidance
Use these worked steps alongside the part-by-part answers. They explain the method and mark allocation; they do not add extra marks.
- (a) Connect majority small deflection to nucleus much smaller than atom.
- (a) Connect positive-alpha repulsion to positive nuclear charge.
- (a) Connect rare large angles to concentration of mass and charge.
- (a) Reject diffuse positive charge using inadequate strong localized force.
- (b) Place protons and neutrons in nucleus; electrons outside.
- (b) UseZ=10 for both protons and neutral electrons.
- (b) UseN=A−Z for10 and12.
- (b) Define same element/Z with differentN.
- (c) State discrete rather than one universal alpha energy for all nuclides.
- (c) State continuous beta distribution.
- (c) Explain variable sharing with a neutral lepton, not different electron rest masses.
- (d) Multiply 55.9 by 1.66×10⁻²⁷.
- (d) Divide 3.32×10⁻²⁶ by 1.66×10⁻²⁷.
- (d) Keep dimensions mass; do not report mass in joules.
- (e) Name positron and mass equality.
- (e) Give equal charge magnitudes with opposite signs.
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