PHYSICS 202 FINAL EXAM Wednesday, May 11, 2005, 8-10 am

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1 PHYSICS 202 FINAL EXAM Wednesday, May 11, 2005, 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: Polarized light, with its polarization axis along the y direction, enters a polarizer whose initial transmission axis is along the x direction. The orientation of the polarizer is then rotated so that the direction of the transmission axis changes. The intensity of the transmitted light will: Increase Stay the same Decrease A2: Can a convex mirror be used to produce an image that is larger than the object? Yes Maybe No A3: If the number of slits per centimeter in a diffraction grating is decreased, the second-order principal maxima: (a) Move toward the central maximum (b) Remain in the same place (c) Move away from the central maximum A4: The maximum speed of the electrons emitted from a metal surface is v A when the wavelength of light incident on the surface is λ A, and the maximum speed is v B when the wavelength is λ B. v A < v B. In which case is the wavelength of the light larger? Case A Case B A5: When an incandescent light bulb is turned on, the tungsten filament becomes white hot. The temperature coefficient of resistivity for tungsten is a positive number. As the filament heats up, the power delivered to the bulb (encircle all that are possible): Increases Stays the same Decreases The figure on the right shows three charges, labeled q 1, q 2, and q 3. A Gaussian surface is drawn around q 1 and q 2. A6: Which charges determine the electric flux through the Gaussian surface? (Encircle all that apply.) q 1 q 2 q 3 A7: Which charges determine the electric field at point P? (Encircle all that apply.) q 1 q 2 q 3

3 A8: The figure at the right shows a copper ring that is about to enter a rectangular region that contains a magnetic field pointing out of the paper. As the ring enters the rectangular region (encircle the correct letter): (a) There will be a clockwise induced current (b) There will be a counterclockwise induced current (c) There will be no induced current A9: (4 points) Suppose there were a greater number of 14 6C atoms in a plant living 4000 years ago than is currently believed. When the seeds of this plant are tested today using radiocarbon dating, the age obtained will be: Too small Just right Too large Section B: Must show your work. Partial credit will be awarded where appropriate. B1: For the circuit shown in the drawing, find the current provided by the generator when the frequency is (a) very large and (b) very small. (a) Current (b) Current

4 B2: Two charges are located on the x axis: q 1 = +6.5 µc at x 1 = +4.5 cm, and q 2 = +6.5 µc at x 2 = 4.5 cm. Two other charges are located on the y axis: q 3 = +3.5 µc at y 3 = +5.5 cm, and q 4 = 8.5 µc at y 4 = +7.5 cm. Find the net electric field (magnitude and direction) at the origin. Magnitude Direction B3: Magnetic resonance imaging (MRI) is a medical technique for producing pictures of the interior of the body. The patient is placed within a strong magnetic field. One safety concern is what would happen to the positively and negatively charged particles in the body fluids if an equipment failure caused the magnetic field to be shut off suddenly. An induced emf could cause these particles to flow, producing an electric current within the body. Suppose the largest surface of the body through which flux passes has an area of m 2 and a normal that is parallel to a magnetic field of 1.8 T. Determine the smallest time period during which the field can be allowed to vanish if the magnitude of the average induced emf is to be kept less than V. Time period

5 B4: A diffraction grating is 1.40 cm wide and contains 2500 lines. When used with light of a certain wavelength, a third-order maximum is formed at an angle of 20.0 o. What is the wavelength (in nm)? Wavelength B5: The membrane that surrounds a certain type of living cell has a surface area of 4.5 x 10-9 m 2 and a thickness of 1.1 x 10-8 m. Assume that the membrane behaves like a parallel plate capacitor and has a dielectric constant of 5.5. (a) The potential on the outer surface of the membrane is mv greater than that on the inside surface. How much charge resides on the outer surface? (b) If the charge in part (a) is due to K + ions (charge +e), how many such ions are present on the outer surface? Total charge Number of ions

6 B6: By using the Bohr model, calculate the atomic number of the element which is likely to emit a K α X- ray with a wavelength of nm. Atomic number B7: Uranium U (atomic mass = u) undergoes α decay. Assuming that all of the released energy is in the form of kinetic energy of the α particle (atomic mass = u) and ignoring the recoil of the daughter nucleus (thorium Th, atomic mass = u), find the speed of the α particle. Ignore relativistic effects. Speed

7 B8: The drawing shows a negatively charged particle entering a 0.55-T magnetic field. The particle has a speed of 280 m/s and moves perpendicular to the magnetic field. Just as the particle enters the magnetic field, an electric field is turned on. What must be the magnitude and direction of the electric field such that the net force on the particle is twice the magnetic force? Direction: Up Down Left Right Into paper Out of paper Magnitude B9: The maximum angular magnification of a magnifying glass is 11.0 when a person uses it who has a near point that is 25.0 cm from his eyes. The same person finds that a microscope, using this magnifying glass as the eyepiece, has an angular magnification of The separation between the eyepiece and the objective lens of the microscope is 23.0 cm. What is the focal length of the objective lens. Focal length