CIE iGCSE Co-Ordinated Science P6.2.3 Galaxies and the Universe Exam Style Questions Paper 4
Question
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P6.2.2 — Life cycle of stars (Part (a))
• Topic P6.2.1 — The Sun as a star (Part (b)(i))
• Topic P2.3.2 — Convection (Part (b)(ii))
• Topic P2.3.3 — Radiation (Part (b)(iii))
• Topic P6.2.3 — Galaxies and the Universe (Part (c))
▶️ Answer/Explanation
(a) New stars, planets, or protostars may form from a nebula.
The material from a supernova explosion forms a nebula (cloud of gas and dust), which can collapse under gravity to form new stars and planetary systems.
(b)(i) Energy release in a star:
• Energy is released by nuclear fusion.
• Hydrogen nuclei fuse together to form helium nuclei.
• This process releases vast amounts of energy in the form of electromagnetic radiation (including light and heat).
(b)(ii) Convection in the Sun’s outer layers:
• Hot gas near the core becomes less dense and rises.
• As it rises, it cools and becomes more dense.
• The cooled gas sinks back down, creating convection currents that transfer energy outward.
(b)(iii) Surface design to limit temperature:
• Colour: White or silver (to reflect most incident radiation)
• Texture: Shiny or smooth (to reduce absorption of radiation)
Light colours reflect more radiation (poor absorbers), while shiny surfaces are poor emitters of thermal radiation.
(c) Completed sentences:
The Universe initially expanded from a place of high density (or temperature).
The Universe is still expanding.
The Universe is approximately 13.8 billion years old.
Question
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P6.2.3 — Galaxies and the Universe / Big Bang Theory (Part (a)(i) & (a)(ii))
• Topic P6.2.1 — The Sun as a star / Speed of light calculations (Part (b))
• Topic P5.2.3 — Radioactive decay / Alpha decay equations (Part (c)(i))
• Topic P5.2.4 — Half-life calculations (Part (c)(ii))
▶️ Answer/Explanation
(a)(i) 13.8 billion years
According to the Big Bang Theory, the Universe is approximately 13.8 billion years old, determined from cosmic microwave background radiation and the expansion rate of the Universe.
(a)(ii) The Universe began from a single point of extremely high temperature and density, which then expanded rapidly.
The Big Bang Theory states that all matter and energy in the Universe were initially concentrated in a singularity. This singularity then expanded and continues to expand today.
(b) Shortest distance = \( 5.6 \times 10^{10} \) m
\( \text{time} = \frac{\text{distance}}{\text{speed}} = \frac{5.6 \times 10^{10}}{3.0 \times 10^8} = 1.87 \times 10^2 = 187 \text{ s} \)
The shortest possible time uses the minimum distance between Earth and Mars. Light travels at \( 3.0 \times 10^8 \) m/s in a vacuum.
(c)(i) \( ^{210}_{84}\text{Po} \rightarrow ^{206}_{82}\text{Pb} + ^{4}_{2}\alpha \)
Alpha decay reduces both the mass number and atomic number. The mass number decreases by 4 (210 → 206) and the proton number decreases by 2 (84 → 82), forming lead (Pb).
(c)(ii) Number of half-lives = \( \frac{12.4}{3.1} = 4 \)
\( \text{Mass remaining} = \frac{560}{2^4} = \frac{560}{16} = 35 \text{ g} \)
After 4 half-lives, the mass has halved four times: 560 → 280 → 140 → 70 → 35 g. The remaining mass is 35 g.