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My Favourite LC questions (part 3): The Physics of Christmas Baubles


Not really a favourite, this one. But at least it has (something approaching) a Christmas theme.


I speak, of course, of 2014 q.12b, which involved a reflective Christmas bauble and asked students to find an image formed by it, treating it as a convex mirror.


Its quite difficult, with two likely pitfalls for even a well prepared student: the negative values of v and f, and the fact that the focal length is 1/4 the diameter. Many instinctively halved it instead, which in itself is a good example for students as to why they should always draw diagrams.


I'm using it to introduce a (not very festive) Christmas theme to a few classes today and tomorrow. Its available here, if you wish to do the same, under the heading 'Christmas baubles'


Enjoy the holidays!

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The derivation of key formulae is something that features every year in a few leaving cert questions - which I'm inclined to think is a good thing. By knowing where even a few formulae come from, stu