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PHYSICS 202 – FINAL EXAM Monday, May 7, 2007 NAME: SECTION: Note: 509 510 511 512 509 Recitation Recitation Recitation Recitation 510 Tues Tues Tues Tues 511 512 8:00 9:35 11:10 12:45 There are a total of 16 problems on this test. For each problem, write your answer in the space provided. You may use the backs of the pages for scratch calculations if you wish, but only the work in the spaces provided on the front of the pages will be graded. Problems A1 through A7 are worth 4 points each. For these seven problems, you do not need to show calculations or explain your reasoning unless requested. Also, no partial credit will be awarded for incorrect answers. Problems B1-B9 are worth 8 points each. For these nine problems, you must show your work and/or explain your reasoning to receive any credit for a problem. Merely stating the answer is NOT sufficient. Partial credit will be awarded where appropriate. Also, to receive full credit in this part: • Numerical answers should be given with 3 significant figures and be correct to within 2%. • An answer can not be completely correct if it has the wrong units! GOOD LUCK !!!!! Additional information not on the standard Final Exam equation sheet: NA = 6.022 x 1023 molecules/mole 14 C T1/2 = 5730 yr In living tissue: 0.255 Bq/(gm C) Section A: Encircle the correct answer(s). Note that there may be more than one correct answer to a question. No partial credit will be awarded. A1: The figure shows a gold leaf electroscope. It consists of a metal tube with a metal ball at the top and a sheet of extremely thin gold leaf at the other end. The gold leaf is fastened in such a way that it is free to pivot about its upper edge. Assume the gold leaf hangs straight downward prior to the experiment in part (a). (a) (2 points) If you bring a charged rod close to the metal ball at the top without touching it, the gold leaf: Pivots outward Hangs straight downward (b) (2 points) Now you touch the charged rod to the metal ball for a second or so. After you then remove the charged rod, the gold leaf: Pivots outward A2: Hangs straight downward The two coils shown in the figure are parallel to each other and are connected to batteries. Coil A is held in place. Coil C is free to move. After the switch S is closed, Coil C will initially move: Toward Coil A Away from Coil A Into the paper Out of the paper Upward Downward A3: A square loop of wire is pulled upward out of the space between the poles of a magnet, as shown in the figure. As this is done, the current induced in this loop, as viewed from the N pole of the magnet, will be directed: Clockwise Counterclockwise Zero A4: A series R-L-C circuit is powered by an ac sinusoidal voltage source. Encircle the phase diagram that illustrates the relationship between the current i and the potential drop vC across the capacitor: A5: An object lies outside the focal point of a converging lens. Which of the following statements about the image formed by this lens must be true? (a) The image is always real and inverted. (b) The image could be real or virtual, depending on how far the object is past the focal point. (c) The image could be erect or inverted, depending on how far the object is past the focal point. (d) The image is always on the opposite side of the lens from the object. A6: Laser light of wavelength λ passes through a thin slit of thickness a and produces its first dark fringes at angles of ±450 with the original direction of the beam. The slit is then replaced by a circle of diameter a. When the same laser light is passed through the circle, the first dark fringe occurs at ±59.60 ±54.90 ±36.90 ±35.40 A7: Suppose that a person who has one hand in a uniform beam of x rays receives a dose of 90 millirem (mrem) in 30 s. This person now puts both hands side by side in the beam for 30 s. Assuming the beam is wide enough to cover both hands equally, the radiation dose that she will receive during the second 30 s period is: 180 mrem 90 mrem 45 mrem Can’t tell Section B: Must show your work. Partial credit will be awarded where appropriate. B1: A point charge of -5.00 nC is at the origin, and a second point charge of +7.00 nC is on the x axis at x = 0.800 m. Find the magnitude and direction of the electric field at the point x = 30.0 cm on the x axis. Direction: +x -x Magnitude ________________________________ +y -y B2: A point charge Q = +4.80 μC is held fixed at the origin. A second point charge q = +1.40 μC with mass of 2.80 x 10-4 kg is placed on the x axis, 0.250 m from the origin. (a) What is the electric potential energy U of the pair of charges? (Take U to be zero when the charges have infinite separation.) (b) The second point charge is released from rest. What is its speed when its distance from the origin is 1.00 m? Potential energy __________________________ Speed __________________________________ B3: A circular coil of wire with average radius 0.0630 m and 30 turns lies in the plane of the paper. It carries a current of 6.00 A in a counterclockwise sense. The coil is in a uniform 1.20 T magnetic field directed toward the right. Find the magnetic moment of the coil and the torque on the coil. Magnetic moment ____________________________________ Torque ___________________________________ B4: An inductor used in a dc power supply has an inductance of 8.00 H and a resistance of 180 Ω and carries a current of 0.450 A. (a) How much energy is stored in the inductor? (b) At what rate is thermal energy developed in the inductor? (c) From your answers to parts (a) and (b), what can you say about the change in the magnetic field energy with time? Stored energy ____________________________________________ Rate of thermal energy _____________________________________ Magnetic energy is: Increasing Decreasing Can’t tell B5: We can reasonably model a 40 W incandescent lightbulb as a sphere 6.0 cm in diameter. Typically, only about 3% of the energy goes to visible light; the rest goes largely to nonvisible infrared radiation. What is the visible light intensity in W/m2 at the surface of the bulb? What are the amplitudes of the electric and magnetic fields of the visible light at this surface? Light intensity _______________________________________ Electric field amplitude ________________________________ Magnetic field amplitude _______________________________ B6: You have a microscope that is 20.0 cm long between the objective and eyepiece lenses. The objective lens has a focal length of 9.00 mm. The microscope forms its final image at infinity. What should be the focal length of the eyepiece lens for this microscope to have an overall magnification of 150x? Focal length ___________________________________ B7: Rumor has it that the US military has spy satellites in orbit carrying telescopes that can resolve objects on the ground as small as 15.0 cm. If we assume that such satellites orbit about 400 km above the ground and that they focus light of wavelength 500 nm, what would have to be the minimum diameter of the mirror (or objective lens)? Diameter _________________________________ B8: The photoelectric work function of potassium is 2.3 eV. If light having a wavelength of 220 nm falls on potassium, find the stopping potential (in volts), the kinetic energy (in electron volts) of the most energetic electrons ejected, and the maximum speed of the ejected electrons. Stopping potential ______________________________ Kinetic energy _________________________________ Speed ________________________________________ B9: A sample of charcoal from an archaeological site contains 55.0 gm of carbon and decays at a rate of 0.778 Bq. How old is it? Age ________________________________________