RelativityR - 1. SL and HL Although many candidates defined...

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1. SL and HL Although many candidates defined proper length correctly, there was much confusion with the definition of proper time. Some definitions were unclear, vague, approximate, incomplete or wrong. A typical wrong (confused definition) would be “time as measured in an inertial reference frame”. Most candidates suggested that the events would not be simultaneous for Carmen, indicating that event A will happen first. However, in the following explanation it was rarely stated that c is independent of the motion of the source or the observer, an essential fact in the argument. Many of the candidates also tended to jump from one frame to another thus seriously weakening the argument. At times the situation was over simplified and the subtleties of the concepts involved not appreciated. Some candidates incorrectly used the principle of causality to negate the possibility of non-simultaneity. Using the equation for length contraction, many candidates calculated the speed correctly but some candidates did not identify the proper length. However, most candidates appreciated that neither observer could be considered to have the “correct” viewpoint. 2. SL and HL The curve was generally well drawn, becoming asymptotic to the “c line”, but a large number of candidates described the behaviour of the curve itself instead of using the principles of relativistic mechanics as suggested in the question. A few candidates briefly suggested the fact that the mass of the electron increases with speed, but did not elaborate. The calculation of the electron mass and its total energy was sometimes done well but quite often was not started. Clearly, some candidates were familiar with these types of calculation and the others were not. 3. HL only It is recognised that spacetime diagrams are not on the syllabus as such but it also recognised that they are a very useful concept. In this question, the diagram was meant to aid the candidates with their answer. However, it would probably have been preferable to let the candidates choose their own way to answer the question. Needless to say, full credit was given for a verbal description irrespective of what or whether a diagram was drawn. Answers in terms of the warping of spacetime were generally sound and it should be noted that a non-relativistic description of a black hole was given credit. 1
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4. SL and HL Most candidates did appreciate that in defining proper length, the observer must be at rest with respect to the object. However, many answers to proper time involved being ‘at rest to measure a time’ rather than a time interval in a reference frame where the two events defining the interval occur at the same place. Many candidates thought that an inertial observer must be at rest rather than in a reference frame moving at constant velocity. In general, the half-life was calculated successfully and most candidates gave a correct
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RelativityR - 1. SL and HL Although many candidates defined...

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