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Date May 2017 Marks available 2 Reference code 17M.3.HL.TZ1.16
Level Higher level Paper Paper 3 Time zone 1
Command term Discuss Question number 16 Adapted from N/A

Question

Outline, with reference to star formation, what is meant by the Jeans criterion.

[2]
a.

In the proton–proton cycle, four hydrogen nuclei fuse to produce one nucleus of helium releasing a total of 4.3 × 10–12 J of energy. The Sun will spend 1010 years on the main sequence. It may be assumed that during this time the Sun maintains a constant luminosity of 3.8 × 1026 W.


Show that the total mass of hydrogen that is converted into helium while the Sun is on the main sequence is 2 × 1029 kg.

[2]
b.

Massive stars that have left the main sequence have a layered structure with different chemical elements in different layers. Discuss this structure by reference to the nuclear reactions taking place in such stars.

[2]
c.

Markscheme

a star will form out of a cloud of gas

when the gravitational potential energy of the cloud exceeds the total random kinetic energy of the particles of the cloud
OR
the mass exceeds a critical mass for a particular radius and temperature

[2 marks]

a.

number of reactions is  10 10 × 365 × 24 × 3600 × 3.8 × 10 26 4.3 × 10 12 = 2.79 × 10 55

H mass used is  2.79 × 10 55 × 4 × 1.67 × 10 27 = 1.86 × 10 29  «kg»

[2 marks]

b.

nuclear fusion reactions produce ever heavier elements depending on the mass of the star / temperature of the core

the elements / nuclear reactions arrange themselves in layers, heaviest at the core lightest in the envelope

[2 marks]

c.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.

Syllabus sections

Option D: Astrophysics » Option D: Astrophysics (Additional higher level option topics) » D.4 – Stellar processes (HL only)
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Option D: Astrophysics » Option D: Astrophysics (Additional higher level option topics)
Option D: Astrophysics

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