Part I: Multiple-Choice

Transcription

1 Part I: Multiple-Choice Circle your anwer to each quetion. Any other ark will not be given credit. Each ultiple-choice quetion i worth point for a total of 0 point. 1. The dead-quiet caterpillar drive for ubarine a een in the ovie The Hunt for Red October i baed on a agnetohydrodynaic (MHD) drive. A the hip ove forward, eawater flow through ultiple channel (one of which i hown below) in a tructure built around the rear of the hull. Magnet (hown but not labeled) are poitioned along oppoite ide of the channel with oppoite pole facing each other; create a agnetic field within the channel. Electrode create an electric field acro the channel a hown. The electrode drive a current acro the channel and through the water, the agnetic field propel the water toward the rear of the channel creating a propulion yte. What direction hould the agnetic field be oriented o the water i propelled out the back of the channel? a. upward b. downward c. to the right d. to the left. A current of 17A i aintained in a ingle circular loop with a circuference of. A agnetic field of 0.8T i directed parallel to the plane of the loop. The agnitude of the torque on the loop i due to the agnetic field i a. zero b N c N d N 3. In vacuu, the peed of light depend on a. the frequency of light. b. the wavelength of light. c. all of the above. d. none of the above.

2 4. A long-traight current carrying wire that ha 6 A of current pae through the center of a circular coil of wire of radiu 5c. The wire i perpendicular to the plane of the coil. If the current in the wire increae at a rate of 1 A/, the induced current generated in the coil i a. 6A clockwie for a 1 reitance coil. b. 6A counterclockwie for a 1 reitance coil. c. zero. d. unable to be deterined ince the direction of the current in the wire i unknown. 5. Two conducting loop face each other a ditance d apart. An oberver ight along their coon axi fro left to right. If a clockwie current i uddenly etablihed in the larger loop by a battery not how, the direction of the induced current in the aller loop i a. zero. b. clockwie c. counterclockwie d. unable to be deterined ince the agnitude of i i unknown. 6. A Boeing KC-135A refueling airplane ha a wingpan of 39.9 and flie at a contant altitude in a northerly direction with a peed of 850 k/hr. If the vertical coponent of the Earth agnetic field i 5.0x10-6 T, what i the induced ef between the wing tip? a. 0 V b. 1 V c. 47 V d. 170 V

3 7. Your eye ee in a typical wavelength range of 400n 700n. A typical edical x-ray ha a wavelength of approxiately a. 800 n b. 300 n c. 1x10 9 n d. 0.1 n 8. A icrowave oven i powered by an electron tube called a agnetron, which generate icrowave with a frequency of.45 GHz. (Giga tand for a billion.) The icrowave enter the oven and are reflected by the wall. The tanding-wave pattern produced in the oven can cook food unevenly with hot pot in the food at antinode and cool pot at the node, o a turntable i often ued to rotate the food and ditribute the energy. If a icrowave oven intended for ue with a turntable i intead ued with a cooking dih in a fixed poition, the antinode appear a burn ark on the food. If the eparation ditance between the burn i eaured to be 6c, what i the peed of the icrowave? a. 3x10 8 / b. 1.5x10 8 / c.1.5x10 10 / d..5x10-11 / 9. A plane flie at contant peed due north through the Earth agnetic field that ha coponent that point both north and vertically down. In thi ituation, a. the left ide of the plane becoe poitively charged. b. the right ide of the plane becoe poitively charged. c. the top of the plane becoe poitively charged. d. the botto of the plane becoe poitively charged. 10. A wooden ring i dropped vertically through a region of pace containing a agnetic field, hown below right. Due to electroagnetic induction only, the direction of the current in the ring i A a. clockwie. b. counterclockwie. c. alternating both clockwie and counterclockwie. X X X B d. zero.

4 Part II: Free Repone Proble Pleae how all work in order to receive partial credit. If your olution are illegible no credit will be given. Pleae ue the back of the page if neceary, but nuber the proble you are working on. The nuber in parenthee following the quetion correpond to the point value for each part. 1. The olar wind i a trea of charged particle, ainly proton and electron that are ejected fro the Sun and travel outward through pace. When the olar wind encounter the agnetic field of the Earth the charged particle piral down the agnetic field line near the pole and excite ato in the atophere cauing the aurora. Suppoe that the proton and the electron in the olar wind are traveling with a velocity of 6.5x10 6 /. and enter the Earth agnetic field (5.5x10-5 T directed traight down at the North Pole) at an angle of 65.5 o with repect to the field. a. Starting with F = a, derive an expreion for the period of the circular orbit for any charged particle. (Hint: The period i the tie it take the charged particle to ake one coplete trip the circular loop.) (8) F B F C T qb qv B v R qbr v R T b. What i the period of the electron orbit? Of the proton orbit? (6) Tp C T Te C T c. The reultant otion of the charged particle i a helix around the agnetic field line. Derive an expreion for the pitch of the helix, where the pitch i defined a the ditance the particle travel parallel to the agnetic field in one revolution about the agnetic field line. (6) p vllt vcot

5 d. What i the pitch of the electron orbit? Of the proton orbit? (6) p p e p co 65.5 co A light bulb in a circuit, hown below in the ketch, ha a reitance of 1 and conue 5W of power where a 1.5 long rod ove to the right with a contant peed of 3.1 /. a. What i the agnetic field that will produce thee reult above? (8) P I R BLv R B PR L v 5W T out of the page. b. What external force i needed to pull the rod to the right at thi peed? (6) T B L v Fext FB ILB 1. 61N to the right. R 1 c. What i the agnitude and direction of the current that flow in the circuit? (6) BLv I R R in agnetic flux. T A 650Acounterclockwie to oppoe the increae d. Doe all of the echanical work done by the external force get tranfored to theral energy in the wire? (5) At firt glance, the anwer hould be ye ince the echanical work per unit tie the external force doe i converted to electrical energy per unit tie which i converted to theral energy

6 in the wire and the wire heat up. However, not only doe the wire heat up a heat i diipated by the converion of electrical energy to theral energy, but a all aount of thi energy i alo tranfored in to light ince the charge in the wire are accelerated by the induced electric field and the external agnetic field. 3. Rail gun have been uggeted for launching projectile into pace without the need for cheical rocket, and for ground to air antiiile weapon of war. A crude tabletop (hand-held) odel i hown below. When the trigger i queezed cloed current flow in the circuit and the 500-g projectile are fired off of the end of the rail at the target. 100c Trigger 3.5c a. What i the agnetic field created at the idpoint of the bar if a 60-A current flow through the circuit? (Hint: Aue that the field at the idpoint i due only to agnetic field created by current flowing in the top and botto rail, which can be odeled a two long traight wire.) (8) I T 60A Bnet Bupper Blower A T 1. 37T r into the page b. What are the agnetic force and correponding acceleration of the bar? (8) F ILB 60A T a F 0.009N N.9N both to the right. c. If the projectile are accelerated fro ret over a ditance of 1 eter, with what velocity (in / and i/hr) do the projectile leave the rail? (6) 0.009N 1 Fx i W Fx 1 v v hr to the right.

7 d. Suppoe that the peed in part c i too all for your liking. Suppoe that you would like the projectile to leave the rail at 850 ile per hour (about 394 /), what current would you need to produce thi peed? (Note: The allet working odel of thee have been developed by the Navy and are being teted on battlehip. Alo for a great rendition of a tabletop odel, watch the ovie Eraer with Arnold Schwarzenegger.) (7) W Fx I 1 0 v rv x L v 0I F ILB IL x r T A 6965A