CIE iGCSE Co-Ordinated Science P6.2.2 Life cycle of stars Exam Style Questions Paper 4
Question
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P6.2.2 — Life cycle of stars (Parts (a) & (b))
• Topic P6.1 — The Solar System (Part (c)(i) & (c)(ii))
• Topic P5.2.2 — The three types of nuclear emission (Part (d))
▶️ Answer/Explanation
(a) The Big Bang Theory describes the beginning of the Universe as an expansion from a single point of very high density and very high temperature.
According to this theory, the Universe began approximately 13.8 billion years ago and has been expanding ever since.
(b) Very large mass stable star → red supergiant → supernova → black hole.
• A very large mass star becomes a red supergiant as it expands.
• It then undergoes a supernova explosion.
• The core collapses to form a black hole (if sufficiently massive).
(c)(i) Most of the mass of the Solar System is located in the Sun.
The Sun contains approximately 99.8% of the total mass of the Solar System.
(c)(ii) As orbital radius increases, orbital speed decreases.
The strength of the Sun’s gravitational field decreases with distance, so planets further from the Sun travel more slowly in their orbits.
(d) First type of radiation: Alpha (α) radiation.
Explanation: The count rate decreases from 240 to 180 when paper is placed between the source and detector. Alpha radiation is stopped by paper, so this reduction indicates the presence of alpha particles.
Second type of radiation: Gamma (γ) radiation.
Explanation: After passing through paper and 5 mm aluminium, the count rate remains above background (181 counts/min compared to background 14 counts/min). Gamma radiation is highly penetrating and is only significantly reduced by thick lead (10 cm lead reduces the count to 22, which is close to background). This confirms the presence of gamma radiation.
Question
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P5.2.3 — Radioactive decay
• Topic P5.2.4 — Half-life
• Topic P5.2.5 — Applications and safety precautions
• Topic P6.2.2 — Life cycle of stars
▶️ Answer/Explanation
(a) ¹⁴C → ⁰₋₁β + ¹⁴₇N
Beta decay involves a neutron converting into a proton and emitting a beta particle (electron). The mass number remains unchanged, but the atomic number increases by one.
(b) beta ; (beta) penetrates through thin aluminium foil (to be detected) / (beta) absorbed by thick aluminium foil (so not detected)
Beta radiation has intermediate penetrating power. It is suitable for thickness monitoring because the amount of radiation reaching the detector changes with foil thickness. Alpha would be completely absorbed, while gamma would pass through unaffected.
(c) 11,400 years
Activity has fallen from 28 to 7 counts/min
28 → 14 → 7 (2 half-lives)
Age = 2 × 5700 = 11,400 years
Each half-life reduces the activity by half. After two half-lives, the activity is a quarter of the original.
(d)(i) fusion
Stars produce energy through nuclear fusion, where lighter nuclei combine to form heavier nuclei, releasing enormous amounts of energy.
(d)(ii) helium ; and any named product heavier than hydrogen but lighter than iron ; energy
In stable stars, hydrogen nuclei fuse to form helium. In larger stars, further fusion produces heavier elements up to iron. Energy is released during these fusion reactions.