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Question 19N.3.HL.TZ0.17

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Date November 2019 Marks available [Maximum mark: 7] Reference code 19N.3.HL.TZ0.17
Level HL Paper 3 Time zone TZ0
Command term Describe, Discuss, Estimate Question number 17 Adapted from N/A
17.
[Maximum mark: 7]
19N.3.HL.TZ0.17
(a)

Proxima Centauri is a main sequence star with a mass of 0.12 solar masses.

Estimate lifetime on main sequence of Proxima Centaurilifetime on main sequence of Sun.

[2]

Markscheme

realization that lifetime T∝massluminosity ✔

TT⊙=MM⊙-2.5=0.12-2.5=200 ✔

(b)

Describe why iron is the heaviest element that can be produced by nuclear fusion processes inside stars.

[2]

Markscheme

the binding energy per nucleon is a maximum for iron ✔

formation of heavier elements than iron by fusion is not energetically possible ✔

NOTE: For MP2 some reference to energy is needed

(c)

Discuss one process by which elements heavier than iron are formed in stars.

[3]

Markscheme

ALTERNATIVE 1 — s-process
s-process involves «slow» neutron capture ✔
in s-process beta decay occurs before another neutron is captured ✔
s-process occurs in giant stars «AGB stars» ✔
s-process terminates at bismuth/lead/polonium ✔


ALTERNATIVE 2 — r-process
r-process involves «rapid» neutron capture ✔
in r-process further neutrons are captured before the beta decay occurs ✔
r-process occurs in type II supernovae ✔
r-process can lead to elements heavier than bismuth/lead/polonium ✔

NOTE: If the type of the process (r or s/rapid or slow) is not mentioned, award [2 max].

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