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第17届国际物理奥林匹克竞赛实验试题及解答（英文）
INSTRUCTIONS AND INFORMATION
1. Adjust collimator to produce parallel light. This may be performed by the following sequence of operations:
(a) Focus the telescope on a distant object, using adjusting knob on telescope, so that the cross hairs and object are both in focus.
(b) Position the telescope so that it is opposite the collimator with slit illuminated so that the slit can be viewed through the telescope.
(c) Adjust the position of the collimator lens, using the adjusting knob on the collimator, so that the image of the slit is in focus on the cross hairs of the telescope's eyepiece.
(d) Lock the spectrometer table, choosing an appropriate 'zero' on the vernier scale, so that subsequent angular measurements of the telescope's position can conveniently be made.
2. Remove the eyepiece from telescope and place black plastic stops symmetrically over both ends of the telescope, using the elastic bands, so that the angle of view is reduced.
3. Open up collimator slit.
4. Use the syringes to suspend, vertically, a pendant drop symmetrically above the centre of the spectrometer table so that it is fully illumi¬nated by the light from the collimator and can be viewed by telescope.
5. The central horizontal region of the suspended drop will produce rainbows as a result of two reflections and k (k = 1,2,...) internal reflections of the light. The first order rainbow corresponds to one internal reflection. The second order rainbow corresponds to two
Internal reflections. The k'th order rainbow corresponds to k internal reflections. Each rainbow contains all the colours of the spectrum. These can be observed directly by eye and their angular positions can bed accurately measured using the telescope. Each rainbow is due to white light rays incident on the drop at a well determined angle of incidence, that is different for each rainbow.
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