Free Stars & the Universe questions for IGCSE Physics (0625), part of Space physics. Each question has the answer and the marking points an examiner would look for.
Generate a full Stars & the Universe worksheet →All Space physics questionsStars form and change during their life cycles.
1 Light from distant galaxies is shifted towards the blue end of the spectrum.
2 A star much more massive than the Sun may end as a black hole after a supernova.
3 A star is stable when the inward force of gravity is balanced by the outward pressure from fusion.
Which statements are correct?
Answer: B
Stars much more massive than the Sun follow a different life cycle.
Describe the life cycle of a massive star after the main sequence.
Explain how the elements heavier than iron were formed.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | red supergiant → supernova → neutron star or black hole red supergiant B1 supernova B1 neutron star or black hole B1 | 3 |
| (b) | in supernova explosions in supernovae B1 | 1 |
This question is about orbits and the expanding Universe.
A planet orbits the Sun at an average distance of 7.8 × 108 km. It takes 12 years to complete one orbit. Calculate its average orbital speed in m/s. [1 year = 3.16 × 10⁷ s]
Explain why the orbital speed of a comet changes as it moves along its elliptical orbit.
A distant galaxy is 1.0 × 1024 m from Earth. The Hubble constant is 2.2 × 10⁻¹⁸ s⁻¹. Calculate the speed at which the galaxy is moving away from Earth.
Explain how the observation of redshift supports the Big Bang Theory.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | 12900 m/s r = 7.8 × 1011 m and T = 3.79 × 108 s C1 v = 2πr/T C1 12900 m/s A1 | 3 |
| (b) | faster closer to the Sun; gravitational potential energy converted to kinetic energy it speeds up as it approaches the Sun and slows as it moves away B1 gravitational potential energy is converted to kinetic energy (and back), total constant B1 | 2 |
| (c) | 2.20 × 106 m/s v = H₀d C1 2.20 × 106 m/s A1 | 2 |
| (d) | light from distant galaxies is redshifted; more distant galaxies more redshift so receding faster; universe expanding from a point light from distant galaxies has longer wavelengths than expected (redshift), so they are moving away B1 more distant galaxies have greater redshift, so the Universe is expanding (from a single point) B1 | 2 |
Light from distant galaxies shows redshift.
State what is meant by redshift.
Explain how redshift supports the Big Bang theory.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | increase in observed wavelength the observed wavelength of light is longer than the emitted wavelength B1 | 1 |
| (b) | galaxies moving away; universe expanding almost all galaxies show redshift, so they are moving away from us B1 the further away, the greater the redshift, so the Universe is expanding B1 | 2 |
This question is about stars and the Universe.
Describe the life cycle of a star much more massive than the Sun, after it leaves the main sequence.
Light from distant galaxies is red-shifted. Explain what this means and what it shows.
A galaxy is 1.2 × 1024 m away. The Hubble constant is 2.2 × 10−18 per second. Calculate the speed at which it is moving away.
State what is meant by cosmic microwave background radiation (CMBR) and explain how it supports the Big Bang theory.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | red supergiant; supernova; neutron star or black hole becomes a red supergiant B1 explodes as a supernova B1 leaving a neutron star or a black hole B1 | 3 |
| (b) | wavelength increased; galaxy moving away the observed wavelength is longer than the emitted wavelength B1 the galaxy is moving away from us B1 | 2 |
| (c) | 2.6 × 106 m/s v = H₀d = 2.2 × 10−18 × 1.2 × 1024 C1 2.6 × 106 m/s A1 | 2 |
| (d) | microwave radiation from all directions; remnant of early hot Universe, stretched by expansion microwave radiation detected from all directions in space B1 it is radiation from the hot early Universe, stretched to longer wavelengths by expansion B1 | 2 |
The Sun is a medium-sized star.
Name the process that releases energy in the Sun.
State what is meant by a light-year.
The Milky Way is about 100 000 light-years across. Explain what this tells you about the time for light to cross it.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | nuclear fusion nuclear fusion (of hydrogen into helium) B1 | 1 |
| (b) | distance light travels in one year the distance travelled by light in a vacuum in one year B1 | 1 |
| (c) | 100 000 years light takes about 100 000 years to cross the galaxy B1 | 1 |
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