Stellar PhysicsR - 1. SL and HL Many candidates gave...

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1. SL and HL Many candidates gave correct, alternative labelling for the axes of the H-R diagram and were also able to identify the correct nature of the four stars. It is appreciated that that the information given only enables one to deduce that star B is larger than star A, not more massive. However, there was no evidence to suggest that this confused candidates and the marking scheme was modified such that candidates who got as far as “larger”, were given full credit. Having said this, many candidates correctly deduced the greater area of B from its luminosity and temperature and went on to say that therefore the mass would be greater. These candidates were of course, also given full credit. As mentioned above, candidates who did not think to establish a ratio, had a great deal of difficulty in showing that star B is about 700 pc from Earth and often resorted to some very creative arithmetic. “Too far away” was not an acceptable answer as to why the distance of star B from Earth could not be determined by parallax. 2. HL only This was generally well answered although some candidates got tied up in trying to explain the difference between a white dwarf and neutron star. 3. SL only With few exceptions, the orders were correct and candidates were given full credit. 4. SL and HL In general, in explaining parallax angle and its measurement a diagram was drawn. However, many defined the parsec, rather than the parallax angle. Those candidates who did define parallax angle frequently failed to appreciate that observations of the star at a six-monthly interval would give twice the parallax angle. The calculation of the distance of the star from Earth was completed successfully by the great majority of candidates but few defined apparent brightness correctly. Many stated that it is the brightness observed from Earth or referred to energy received on Earth, rather than power per unit area. The determination of the ratio proved difficult. The majority of answers included a correct expression. However, there were few correct responses. Many candidates found difficulty with either the substitution or the subsequent arithmetic. There were some very good responses to why the star cannot be either a white dwarf or red giant. 1
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5. HL only With few exceptions candidates appreciated the process that provides energy for the main sequence stars. However, with weaker candidates, there was some confusion between fission and fusion. Most realised that high temperatures are required for fusion. Others also included high pressure. Most candidates realised that the hydrogen would be ‘used up’. In general, answers to the evolution of stars of different masses, were disappointing. Candidates tended to give just a few isolated facts that were not in sequence. Furthermore, very few discussed the role of the Chandrasekhar limit. 6.
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This note was uploaded on 09/21/2009 for the course PHYSICS 2211 taught by Professor Uzer during the Fall '08 term at Georgia Institute of Technology.

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Stellar PhysicsR - 1. SL and HL Many candidates gave...

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