Em Totl hysics 2135 Em 3 April 21, 2015 Key rinted Nme: 200 / 200 N/A Rec. Sec. Letter: Five multiple choice questions, 8 points ech. Choose the best or most nerly correct nswer. 1. C Two long stright wires re prllel nd distnce D prt. oint is locted distnce D to the right of the right-hnd wire. Both wires crry constnt currents in opposite directions, s shown in the digrm. f the mgnitude of the mgnetic field t point is zero, wht is the rtio 1 / 2? [A] ¼ [B] ½ [C] 2 [D] 4 D D 1 2 D 2. The three wires shown crry identicl currents in the directions indicted. For which of the three pths, b, nd c is the line integrl B d d ds equl to zero? [A] only [B], b, nd c [C] b nd c [D] nd b b c 3. A A conducting loop is held sttionry fied distnce from long stright wire crrying chnging current s shown. The chnging current induces counterclockwise current ind in the loop. The current in the stright wire is [A] incresing [B] constnt [C] decresing [D]zero. ind C 4. At certin point in spce nd time, the mgnetic field nd oynting vector of n d d 5 4 2 electromgnetic wve re given by B= (10 T) kˆ nd S = (2.38 10 W/m ) ˆj. Wht is the mgnitude E of the wve s electric field vector t tht position nd time? [A] 7.9310-5 V/m [B] 3.3310-4 V/m [C] 310 3 V/m [D] 10 5 V/m ABCD 5. Wht is this? [A] Lser pig invsion. [B] Electromgnetic Wve igs. [C] The logo of pizzeri ner Melbourne, Austrli. [D] Dr. ringle s worst nightmre... 40 /40 for pge 1
6. (40 points totl) A long, stright conducting wire crries 10 A current. At some instnt in time n electron is moving prllel to this wire with velocity of 220 km/s in the sme direction s the current. At this instnt the electron is 2 cm from the wire. () (10 points) Find the mgnitude nd direction of the mgnetic field generted by the currentcrrying wire t the loction of the electron. y z -e v = 220 km/s - 2 cm = 10 A (b) (15 points) Find the mgnitude nd the direction of the electron s ccelertion t the instnt shown. (c) (15 points) Find the mgnetic field generted by the electron t point t this instnt. oint is 2 cm from the electron nd directly below it. /40 for pge 2
7. (40 points totl) A conducting loop of rdius crries current. oint is on the loop s is distnce 0 from the center of the loop. 0 () (5 points) On the side view in the figure below, drw n rrow indicting the direction of the mgnetic field db t produced only by the current segment ds going into the pge ( ) t the very bottom of the current loop. θ ˆr 0 90-θ θ r side view db (b) (30 points) Use the Biot-Svrt Lw to compute B, the -component of the mgnetic field t, due to the entire current loop. (c) (5 points) The totl mgnitude B of the mgnetic field t is (circle one below) (i) greter thn B (ii) less thn B (iii) equl to B /40 for pge 3
8. (40 points totl) A rectngulr loop of wire of width L, height H, nd resistnce R trvels t constnt speed v into uniform mgnetic field B. The plne of the rectngulr loop is perpendiculr to the mgnetic field which is pointing into the pge. (All solutions MUST strt with OSE s nd MUST be epressed in terms of the given prmeters.) () (15 points) At the moment the rectngulr loop enters the mgnetic field region, n emf is induced which cuses current to circulte round the loop. Clculte the mgnitude of the power dissipted in the loop while it is moving into the mgnetic field. H w L (b) (5 points) Wht is the direction of the induced current (circle one)? (c) (15 points) While the rectngulr loop is entering the mgnetic field region, the right side of the loop eperiences mgnetic force due to the current induced in it. Wht is the mgnitude of the mgnetic force eerted on the right side of the loop? (d) (5 points) Once the loop is entirely in the region of uniform mgnetic field, wht is the mgnitude of the current induced in it. /40 for pge 4
9. (40 points totl) A prticulr Argon ion lser hs n output power of 1W nd emits cylindricl bem with rdius of 0.95 mm. The bem strikes flt surfce 75 cm wy nd is completely bsorbed. All solutions must strt with OSEs, nd ll nswers must include proper units. () (10 points) The bem contins light of mny wvelengths, one of which is 488 nm. Wht is the ngulr frequency of this wvelength? Note: in prt c you cn use E = pt, where t is the time it tkes photon to trvel 0.75 m. (b) (10 points) Wht is the mgnetic field mplitude of the bem? (c) (10 points) How much energy is contined in the bem between the lser nd the bsorbing surfce? (d) (10 points) Wht verge pressure does the bem eert on the completely bsorbing surfce? /40 for pge 5