Table 1 shows the calculated properties of three white dwarfs observed in a star cluster. Fig. 1 is a cross-section through one of them. The values show tha...
Question 1 Report
Table 1 shows the calculated properties of three white dwarfs observed in a star cluster. Fig. 1 is a cross-section through one of them. The values show that a star can contain a large mass in a small volume.
| white dwarf | mass / solar masses | radius / km | surface temperature / K |
|---|---|---|---|
| D1 | 0.55 | 9100 | 8000 |
| D2 | 0.92 | 6900 | 12000 |
| D3 | 1.18 | 5200 | 18000 |
(a) What is the radius of D2? [1]
(b) Describe the relationship between mass and radius in Table 1. [2]
(c) Explain why a white dwarf is very dense. [3]
(d) Give two ways in which a white dwarf differs from a main-sequence star. [4]
Answer Details
(a) D2 has a radius of \(6900\text{ km}\). [1]
(b) As mass increases, radius decreases: from D1 to D3, mass rises from \(0.55\) to \(1.18\) solar masses while radius falls from \(9100\) to \(5200\text{ km}\). [2]
(c) A large amount of stellar mass remains in a white dwarf, but it is compressed into a very small volume. Since density is mass per unit volume, this gives a very high density. [3]
(d) A white dwarf has no significant hydrogen fusion, whereas a main-sequence star produces energy by fusion in its core. A white dwarf is much smaller and is supported by electron degeneracy pressure. Any two clear compared differences gain credit. [4]
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