Physics 2306 Fall 1999 Final December 15, 1999 Name: Student Number #: 1. Write your name and student number on this page. 2. There are 20 problems worth 5 points each. Partial credit may be given if work is clearly shown. Note that some problems are easier than others. 3. Answers MUST have units, where appropriate, assume SI units in problems unless otherwise indicated. 4. During the exam you can use a calculator, but not its programmable features. 5. You will have two hours to work on the exam. 6. The exam is closed book and closed notes. Only the formula sheets provided may be used. Do all your work on the exam itself; other papers will not be graded. 7. By writing your name on this exam, you pledge that you have upheld the Honor Code and have arrived at each answer solely by your own work.
1) What current flows in the following circuit? 2 Ω 5 V 3 V a. 2 A b. 1 A c. 0.5 A d. Can not tell. 2 Ω 2) How long does it take for this capacitor to discharge to half it s original voltage after the switch is closed? 20 kω 10 µf a. 30 s b. 139 s c. 0.14 s d. 0.2 s 3) A truck driving towards you at 30 m/s sounds his 2000 Hz horn. What frequency do you hear it at if you are standing on the street? (Take the speed of sound to be 330 m/s.) a. 2200 Hz b. 2182 Hz c. 1833 Hz d. 1818 Hz
4) The magnitude of the current in the straight wire is increasing. The wire loop: a. Is drawn towards the straight wire b. Is repelled from the straight wire c. Experiences no net force d. Do not have enough information 5) Light is incident onto a flat pool of water (n=1.33) 28 degrees from the horizontal. The angle (in degrees) the refracted light in the water makes with the horizontal is: a. 69 b. 21 c. 48 d. 42 6) Locate the image due to the following arrow object by drawing appropriate rays of light which reflect from the concave spherical mirror. The center of the mirror is shown on the axis.
7) The following LR circuit is driven at 60 Hz. What is the phase angle between the current and voltage provided by the AC source? 8) The following CR circuit has a switch closed at t = 0. Sketch the current as a function of time after the switch is closed. (Indicate clearly on the scale the initial and final values.) I 9) A conducting shell has a net charge of +1 micro-coulomb on it. Inside the shell, but not touching it, is a point charge of +3 micro-coulombs. What is the total surface charge on the inside of the conducting shell? t
10) A listener stands 5 meters from one speaker and 3 meters from another. The speakers are in phase. What is the longest wavelength that will give a minimum in intensity at the listener s position? 11) If I stand exactly midway between two in-phase sound sources, how far must I walk toward one of them to reach the first interference minimum? (The wavelength is 2 m.) 12) A rectangular loop of wire is positioned near a long straight wire as shown. What is the magnitude of the magnetic flux through the loop due to a current, I, in the straight wire? a I b c
13) A parallel plate capacitor with circular plates 0.20 m in diameter and with a gap of 10 3 m is being charged at 2.0 Amps. If the electric field between the plates is uniform, what is the magnitude of the magnetic field between the plates 0.10 m from the axis of symmetry? find magnetic field here 14) An ideal transformer has 1000 primary turns and 200 secondary turns. If the primary is plugged into a 110 V (rms) outlet and the secondary is connected to a resistive load of 30 Ω, what is the rms current drawn from the primary? 15) A camera lens with index of refraction 1.3 is coated with a thin film with index of refraction 1.5 to minimize the reflection of light at 600 nm. What is the minimum thickness of the film needed?
16) Two glass plates with index of refraction 1.5 are held apart by two parallel wires separated by 3 cm as shown. When light of 600 nm is passed between the two plates, about 10 dark fringes are observed in the space between the two wires. What is the difference in diameter of the wires? 17) Light of some wavelength is incident upon a 5.0 x 10 5 m wide slit. The angle between the first diffraction minimum on one side of the central maximum and the first minimum on the other side is 1.3 degrees. What is the wavelength of the incident light? 18) Unpolarized light is passed through 4 polarizing films, at least two of which are rotated 90 degrees with respect to each other. What configuration of these four films would pass the largest amount of light, and what fraction of the original intensity is that.
19) Current flows uniformly through a long wire of radius R. Sketch the magnetic field as a function of radius from r = 0 to r = 2R. Magnetic Field Strength 0 R 2R 20) Sketch magnitude and direction of the electric and magnetic fields at an instant in time due to a light wave travelling in the y direction. Make the picture clear! y x z