 AAPT Exams 1998 Physics Olympiad Screening Test (21-30)
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 21 21. The longest wavelength photon in the visible Balmer series for the hydrogen atom is A. 0.66 nm B. 6.56 nm C. 65.6 nm D. 656 nm E. 6560 nm 22 22. Waves are produced by two point sources S and S’ vibrating in phase. See the accompanying diagram. X is a point on the second nodal line. The path difference SX – S’X is 4.5 cm. The wavelength of the waves is approximately A. 1.5 cm B. 1.8 cm C. 2.3 cm D. 3.0 cm E. 4.5 cm 23 23. A thin film of thickness t and index of refraction 1.33 coats a glass with index of refraction 1.50 as shown to the right. Which of the following thicknesses t will not reflect light with wavelength 640 nm in air? Hint: Light undergoes a 180ş phase shift when it is reflected off a material with a higher index of refraction. A. 160 nm B. 240 nm C. 360 nm D. 480 nm E. 640 nm 24 24. An object is placed 12 cm in front of a spherical mirror. The image is right side up and is two times bigger than the object. The image is:A. 6 cm in front of the mirror and real. B. 6 cm behind the mirror and virtual. C. 12 cm in front of the mirror and virtual. D. 24 cm in front of the mirror and virtual. E. 24 cm behind the mirror and virtual. 25 25. A charge is uniformly distributed through a volume of radius a. Which of the graphs below best represents the magnitude of the electric field as a function of distance from the center of the sphere? 26 26. A free electron and a free proton are placed between two oppositely charged parallel plates. Both are closer to the positive plate than the negative plate. Which of the following statements is true? I. The force on the proton is greater than the force on the electron. II. The potential energy of the proton is greater than that of the electron. III. The potential energy of the proton and the electron is the same. A. I only B. II only C. III only D. I & II only E. I & III only 27 27. In the electrical circuit shown below, the current through the 2.0 W resistor is 3.0 A. The emf of the battery is about A. 51 V B. 42 V C. 36 V D. 24 V E. 21 V 28 28. An ion with a charge q, mass m, and speed v enters a magnetic field B and is deflected into a path with a radius of curvature R. If an ion with charge q, mass 2m, and speed 2v enters the same magnetic field, it will be deflected into a path with a radius of curvatureA. 4 R B. 2 R C. R D. (1/2) R E. (1/4) R 29 29. Which of the following wiring diagrams could be used to experimentally determine R using Ohm’s Law? Assume an ideal voltmeter and an ideal ammeter. 30 30. A vertical wire carries a current upward through a magnetic field directed to the north. The magnetic force on the wire pointsA. south B. north C. east D. west E. downward