Hertzsprung-Russell diagram and stellar life cyclesEdexcel A-Level Physics: Subtopic test

1. 1
   A star, R, has a surface temperature of 3200 K and a luminosity 5.0 × 10² times that of the Sun. Astronomers plot its position on a Hertzsprung-Russell (HR) diagram, which shows luminosity against surface temperature.

   (a)

   Which type of star is R most likely to be?

   [1 mark]

   • AA white dwarf
   • BA main-sequence star of similar mass to the Sun
   • CA red giant
   • DA neutron star

   (b)

   Which statement about the axes of a conventional HR diagram is correct?

   [1 mark]

   • ASurface temperature increases from left to right
   • BThe luminosity axis is a linear scale
   • CBoth axes increase from left to right
   • DSurface temperature decreases from left to right

   (c)

   Explain why star R is much more luminous than the Sun even though its surface temperature is lower.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A cloud of cold gas and dust in space collapses and forms a star similar to the Sun, which then spends most of its life fusing hydrogen in its core.

   (a)

   What causes the cloud of gas and dust to collapse?

   [1 mark]

   • AThe gravitational attraction between the particles in the cloud
   • BRadiation pressure from nuclear fusion in the cloud
   • CThe thermal pressure of the hot gas in the cloud
   • DThe magnetic attraction between the dust particles

   (b)

   What happens when the core of the collapsing protostar becomes hot enough for hydrogen to fuse into helium?

   [1 mark]

   • AThe star becomes a red giant
   • BThe star joins the main sequence
   • CThe star becomes a white dwarf
   • DThe star collapses into a neutron star

   (c)

   Explain why the star stays at a constant size and luminosity for most of its life.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A white dwarf has a surface temperature of 12 000 K and a luminosity 1.0 × 10⁻³ times that of the Sun. The luminosity of the Sun is 3.85 × 10²⁶ W.

   (a)

   Calculate the radius of the white dwarf.

   [3 marks]

   (b)

   Describe where the white dwarf lies on an HR diagram, and explain how it formed.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Astronomers compare the life cycle of the Sun, which has a mass of one solar mass, with the life cycle of a star M, which has a mass 20 times that of the Sun.

   (a)

   Describe the life cycle of the Sun from interstellar cloud to its final stage, including its changing position on the HR diagram.

   [6 marks]

   (b)

   Explain how the life cycle of star M, and its position on the HR diagram, differ from those of the Sun.

   [6 marks]

   Total for question 4: 12 marks

End of questions