Fig. 1 shows a simplified life-cycle diagram prepared for a planetarium display. The arrows show how a Sun-like object changes as its nuclear energy source ...
Question 1 Report
Fig. 1 shows a simplified life-cycle diagram prepared for a planetarium display. The arrows show how a Sun-like object changes as its nuclear energy source is used. The star is not moving through space in the diagram.
(a) Name the stage in which hydrogen nuclei fuse to release energy. [2]
(b) Describe how the star changes when it becomes a red giant. [3]
(c) Explain why nuclear fusion in the core eventually decreases. [3]
(d) Give one reason why a white dwarf does not collapse further immediately. [2]
Answer Details
(a) Hydrogen nuclei fuse in a main-sequence star, specifically in its core. [2]
(b) When the star becomes a red giant, its outer layers expand. Its surface becomes cooler and therefore redder. Its luminosity increases because the much larger surface area emits a greater total amount of radiation. [3]
(c) Hydrogen in the core is gradually used up. Less hydrogen is then available as fusion fuel, so fusion releases less energy and produces less outward pressure. [3]
(d) A white dwarf is supported by electron degeneracy pressure, the resistance of closely packed electrons to further compression. This pressure balances the inward gravitational force. [2]
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