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Cambridge Physics for the IB Diploma Extension Worksheet – Option E, Worksheet 2, HL only 1 2 A large, cool cloud of gas may collapse under gravity to form a star. State where the energy comes from to heat up the star so that nuclear fusion may take place. In this question assume a mass–luminosity relation of L M 3.5 . a L is an estimate the lifetime on the main sequence M of a star of mass M and luminosity L. [2] Estimate the lifetime on the main sequence of a star of mass 12 M e in terms of the Sun’s lifetime Te . [2] Suggest why the quantity b 3 [1] The HR diagram below shows two main sequence stars, X and Y, and our Sun. L X Y T 4 5 a Explain how it may be deduced that star X is the most massive of the three stars. [2] b Draw lines on the diagram to show the evolutionary paths of stars X and Y. [2] Two main sequence stars have masses of 2 M e and 10 M e . Compare the evolutionary paths of these two stars with reference to a their final fate. [2] b the intermediate stages in their evolution. [2] c the nuclear reactions taking place in the stars. [3] Outline how the following stars manage not to collapse under their own weight. a A main sequence star. [1] b A white dwarf. [1] c A neutron star. [1] 6 Neutron stars are not shown on an H-R diagram. Suggest a reason for this. [1] 7 State and explain whether the inverse of the Hubble constant underestimates or overestimates the age of the universe. [2] Explain why, in the very early universe, it was not possible to have stable structures such as nuclei and atoms. [2] 8 Copyright Cambridge University Press 2012. All rights reserved. Page 1 of 1