ipho_BUL81The

# ipho_BUL81The - XII International Physics Olympiad Varna...

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XII International Physics Olympiad Varna, Bulgaria, July 1981 The problems and the solutions are adapted by Miroslav Abrashev University of Sofia, Faculty of Physics, 5 James Bourchier Blvd., 1164 Sofia, Bulgaria Reference : O. F. Kabardin, V. A. Orlov, in “International Physics Olympiads for High School Students”, ed. V. G. Razumovski, Moscow, Nauka, 1985. (In Russian). Theoretical Problem 1 A static container of mass M and cylindrical shape is placed in vacuum. One of its ends is closed. A fixed piston of mass m and negligible width separates the volume of the container into two equal parts. The closed part contains n moles of monoatomic perfect gas with molar mass M 0 and temperature T . After releasing of the piston, it leaves the container without friction. After that the gas also leaves the container. What is the final velocity of the container? The gas constant is R . The momentum of the gas up to the leaving of the piston can be neglected. There is no heat exchange between the gas, container and the piston. The change of the temperature of the gas, when it leaves the container, can be neglected. Do not account for the gravitation of the Earth. Theoretical Problem 2 An electric lamp of resistance R 0 = 2 working at nominal voltage U 0 = 4.5 V is connected to accumulator of electromotive force E = 6 V and negligible internal resistance. 1. The nominal voltage of the lamp is ensured as the lamp is connected potentiometrically to the accumulator using a rheostat with resistance R . What should be the resistance R and what is the maximal electric current I max , flowing in the rheostat, if the efficiency of the system must not be smaller than η 0 = 0.6? 2. What is the maximal possible efficiency of the system and how the lamp can be connected to the rheostat in this case? Theoretical Problem 3 A detector of radiowaves in a radioastronomical observatory is placed on the sea beach at height h = 2 m above the sea level. After the rise of a star, radiating electromagnetic waves of wavelength λ = 21 cm, above the horizont the detector registers series of alternating maxima and minima. The registered signal is proportional to the intensity of the detected waves. The detector registers waves with electric vector, vibrating in a direction parallel to the sea surface.

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## This note was uploaded on 11/08/2011 for the course PHYS 0000 taught by Professor Na during the Spring '11 term at Rensselaer Polytechnic Institute.

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ipho_BUL81The - XII International Physics Olympiad Varna...

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