OxfordAQA International GCSE Physics 3.8 Space Physics Exam Questions

About OxfordAQA International GCSE Physics 3.8 Space Physics

Space Physics is the final section of OxfordAQA International GCSE Physics. You study how stars form from dust and gas, why a main sequence star is stable, and how a star's mass determines whether it becomes a white dwarf or explodes as a supernova to leave a neutron star or black hole. You explain how fusion makes the elements and how supernovae spread them. Then you cover the solar system, galaxies, natural and artificial satellites and how gravity keeps objects in orbit. The separate Physics course adds red shift, the expanding universe and cosmic microwave background radiation. Examiners like ordered life cycle answers and evidence for the Big Bang.

What you need to know

• Star formation Gravity pulls together clouds of dust and gas, mainly hydrogen and helium, to form a protostar; smaller masses may form planets. In a main sequence star, hydrogen fuses to helium in the hot, dense core, and the star is stable because the forces within it are balanced.
• Sun-sized stars When hydrogen runs out the star becomes a red giant, sheds its outer layers, becomes a white dwarf and then cools to a black dwarf.
• Massive stars A larger star becomes a red supergiant, fusing helium into carbon and heavier elements such as nitrogen and oxygen, then explodes as a supernova. The core becomes a neutron star or, for the most massive stars, a black hole.
• Making elements Fusion in stars makes the naturally occurring elements up to iron, and elements heavier than iron form in supernovae, which also spread elements through space. The early universe contained only hydrogen.
• Solar system and galaxies Eight planets orbit the Sun, along with dwarf planets, asteroids, comets and moons. The Sun is one star in the Milky Way, and the universe contains thousands of millions of galaxies.
• Orbits Gravity provides the centripetal force for orbits, changing the direction of velocity but not the speed in a circular orbit. Each orbital radius has a particular speed; closer orbits need higher speeds. Artificial satellites use geostationary or low polar orbits.
• Red shift and the Big Bang (separate Physics) Light from distant galaxies is red shifted, and more distant galaxies show greater red shift, so they are moving away faster and space is expanding. This supports the Big Bang model, about 14 thousand million years ago. Cosmic microwave background radiation is radiation from shortly after the Big Bang, and only the Big Bang theory explains it.

Common mistakes in 3.8 Space Physics

• Saying a star is stable because fusion stops it collapsing, without forces. Say the inward gravitational force is balanced by the outward force from the energy released by fusion.
• Saying all stars become black holes. Only very massive stars do; Sun-sized stars end as white dwarfs and then black dwarfs.
• Saying an object in a circular orbit has constant velocity. Its speed is constant but its direction changes, so its velocity changes.
• Saying red shift means the galaxies turn red. It means the wavelength of light is longer than expected.
• Saying elements heavier than iron are made in main sequence stars. They are made in supernovae.

Try three 3.8 Space Physics exam-style questions