PHYSICS 202 FINAL EXAM Wednesday, May 10, 2006, 8-10 am

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1 PHYSICS 202 FINAL EXAM Wednesday, May 10, 2006, 8-10 am NAME: SECTION: Note: 517 Recitation Mon 4: Recitation Wed 10: Recitation Wed 8: Recitation Mon 1:50 There are a total of 18 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-A8 are worth 3 points each. Problem A9 is worth 4 points. For these nine 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. REMINDER: An answer CAN NOT be completely correct if it has the wrong units! G O O D L U C K!!!!! H A V E A G R E A T S U M M E R!!!!!

2 Section A: Encircle the correct answers. No partial credit will be awarded. A1: Suppose the magnetic field of an electromagnetic wave increases in magnitude. In that case, the electric field: Increases Stays the same Decreases Can t tell A2: For which of the following mirror types can an image be projected onto a screen without help from other mirrors or lenses? Concave Convex Both Neither A3: The resistance of an ideal ammeter is: Larger than The same as Smaller than the resistance of an ideal voltmeter. A4: Suppose you were designing an eye and could select the size of the pupil and the wavelengths of electromagnetic waves to which the eye is sensitive. You are considering three options: a. Large pupil and ultraviolet wavelengths b. Small pupil and infrared wavelengths c. Small pupil and ultraviolet wavelengths Order these three choices, from greatest resolving power to least resolving power: abc acb bac bca cab cba A5: An electric potential energy exists when two electrons are separated by a certain distance. When one of the electrons is replaced by a proton, the electric potential energy: Increases Stays the same Decreases A6: A photon of known wavelength strikes a free electron that is initially at rest, and the photon is scattered straight backward. How is the kinetic energy KE of the recoil electron related to the energies E and E of the incident and scattered photons? KE = E E E+E E-E E -E A7: The three charges (+q, +2q, -3q) in the figure below are located at the corners of an equilateral triangle. Sketch in six electric field lines between the three charges.

3 A8: In the figure, a permanent magnet is approaching a loop of wire. A resistor with resistance R is attached to the wire. The direction of the current through the resistor is: From A to B From B to A A9: (4 points) Polonium Po undergoes α decay to produce a daughter nucleus that itself undergoes β - decay. Which of the following nuclei is the one that ultimately results? Pb Tl Tl Bi Pb Section B: Must show your work. Partial credit will be awarded where appropriate. B1: The half-life for the α decay of uranium U is 4.47 x 10 9 yr. Determine the age (in years) of a rock specimen that contains 75% of its original number of U atoms. Age

4 B2: Four point charges have equal magnitudes. Three are positive, and one is negative, as the drawing shows. They are fixed in place on the same straight line, and adjacent charges are equally separated by a distance d. Consider the net electrostatic force acting on each charge. Calculate the ratio of the largest net force to the smallest net force. Ratio B3: A rectangular current loop is located near a long, straight wire that carries a current of 13 A. The current in the loop is 21 A. Determine the magnitude and the direction of the net magnetic force that acts on the loop. Direction: Up Down Left Right Into paper Out of paper Magnitude

5 B4: A circuit consists of an 80 Ω resistor in series with a 4.5 μf capacitor, the two being connected between the terminals of an ac generator. The voltage of the generator is fixed. At what frequency is the current in the circuit one-half the value that exists when the frequency is very large? Frequency B5: Two charges are fixed in place with a separation distance d. One charge is positive and has three times the magnitude of the other charge, which is negative. The positive charge lies to the left of the negative charge. Relative to the negative charge, locate the two spots on the line through the charges where the total potential is zero. First location Second location

6 B6: The width of a slit is 2.3 x 10-5 m. Light with a wavelength of 520 nm passes through this slit and falls on a screen that is located 0.55 m away. In the diffraction pattern, find the width of the bright fringe that is next to the central bright fringe. Width B7: A piece of copper wire is formed into a single circular loop of radius 13 cm. A magnetic field is oriented parallel to the normal to the loop, and it increases from 0 to 0.55 T in a time of 0.35 s. The wire has a resistance per unit length of 3.3 x 10-2 Ω/m. What is the average electrical energy dissipated in the resistance of the wire? Energy

7 B8: In the line spectrum of atomic hydrogen there is a group of lines known as the Pfund series. These lines are produced when electrons excited to high energy levels make transitions to the n = 5 level. Determine the longest and shortest wavelength lines in this series. Longest wavelength Shortest wavelength B9: A farsighted woman breaks her current eyeglasses and is using an old pair whose refractive power is diopters. Since these eyeglasses do not completely correct her vision, she must hold a newspaper cm from her eyes in order to read it. She wears the eyeglasses 2.00 cm from her eyes. How far is her near point from her eyes? Distance