Edexcel International GCSE Physics
Edexcel International GCSE Physics Section 8: Astrophysics Exam Questions
Free Edexcel International GCSE Physics exam questions for Section 8: Astrophysics, with a mark scheme for every pack. Covers galaxies, gravity, orbits, orbital speed, the life cycle of stars, star colour, the HR diagram, red-shift and the Big Bang.
Section 8: Astrophysics exam questions
2 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About Edexcel International GCSE Physics Section 8: Astrophysics
Section 8 is the final section of Edexcel International GCSE Physics and looks at motion in the universe and the life of stars. You need to describe the universe as billions of galaxies, each with billions of stars, explain that gravitational field strength differs on other planets and moons, and describe the orbits of moons, planets, comets and satellites. You also learn how stars evolve, how colour relates to surface temperature, and how stars are classified on the Hertzsprung-Russell diagram. Finally, red-shift and cosmic microwave background radiation are used as evidence for the Big Bang theory. Orbital speed and red-shift calculations are common.
What you need to know
- The universe The universe contains billions of galaxies; a galaxy contains billions of stars. Our solar system is in the Milky Way galaxy.
- Gravity and orbits Gravitational force keeps moons, planets, comets and artificial satellites in orbit. Planets and moons have near-circular orbits; comets have highly elliptical orbits and speed up near the Sun.
- Orbital speed Orbital speed = 2 x pi x orbital radius / time period (v = 2 pi r / T).
- Gravitational field strength g is different on other planets and moons, so the weight of an object changes even though its mass stays the same.
- Life cycle of stars Stars form from nebulae and spend most of their life on the main sequence. Low mass stars become red giants then white dwarfs; high mass stars become red supergiants, explode as supernovae and leave neutron stars or black holes.
- Colour and the HR diagram A star's colour depends on its surface temperature: blue stars are hottest and red stars are coolest. The HR diagram plots absolute magnitude against temperature, showing the main sequence, giants and white dwarfs.
- Red-shift and the Big Bang Light from distant galaxies is red-shifted, Delta lambda / lambda0 = v / c, showing they are moving away. More distant galaxies have greater red-shift. Together with CMB radiation, this supports the Big Bang theory.
Common mistakes in Section 8: Astrophysics
- Thinking comets travel at constant speed. They move fastest when closest to the Sun.
- Forgetting to convert the orbital period into seconds before using v = 2 pi r / T.
- Thinking red stars are hotter than blue stars. Blue stars have the highest surface temperature.
- Saying mass changes on another planet. Mass stays the same; weight changes because g is different.
- Describing red-shift as the galaxy becoming redder in colour. It is an increase in the observed wavelength of spectral lines.
Try three Section 8: Astrophysics exam-style questions
1. The Moon orbits the Earth at a radius of 3.84 x 10^8 m with a period of 27.3 days. Calculate its orbital speed. (3 marks)
Show the mark scheme answer
T = 27.3 x 24 x 3600 = 2.36 x 10^6 s; v = 2 pi r / T = 2 x 3.14 x 3.84 x 10^8 / 2.36 x 10^6; = 1.0 x 10^3 m/s.
2. A spectral line has a wavelength of 656 nm in the laboratory and 669 nm in light from a galaxy. Calculate the speed of the galaxy. Speed of light = 3.0 x 10^8 m/s. (3 marks)
Show the mark scheme answer
Delta lambda = 669 - 656 = 13 nm; v = (Delta lambda / lambda0) x c = (13 / 656) x 3.0 x 10^8; = 5.9 x 10^6 m/s.
3. Describe the evolution of a star with a similar mass to the Sun after the main sequence. (3 marks)
Show the mark scheme answer
It runs out of hydrogen in its core and expands into a red giant; the outer layers are lost; the core becomes a white dwarf.
Section 8: Astrophysics FAQs
What does Edexcel International GCSE Physics Section 8 Astrophysics cover?
It covers the universe and galaxies, gravity and orbits, orbital speed, the life cycle of stars, star colour and the HR diagram, red-shift and the Big Bang theory.
Which paper is Section 8 examined on?
Content from this section can appear on both Paper 1 and Paper 2; statements shown in bold in the specification are only assessed on Paper 2.
What equations do I need for Astrophysics?
Learn orbital speed v = 2 pi r / T and the red-shift equation Delta lambda / lambda0 = v / c, and be confident converting days into seconds.
