PY106 Assignment 7 ( )

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1 1 of 7 3/13/2010 8:47 AM PY106 Assignment 7 ( ) Current Score: 0/20 Due: Tue Mar :15 PM EDT Question Points /3 0/4 0/2 0/2 0/5 0/2 0/2 Total 0/20 Description This assignment is worth 10 points. Each part is worth 1 point. Assume the numbers given in each problem are accurate to three significant figures. WebAssign expects your answers to be accurate within 1%. If you don't round off until the end, and then round off to three significant figures, you should be fine. Occasionally there are errors in WebAssign. If you are convinced your answer is correct and WebAssign is grading you incorrectly please check with Professor Duffy. 1. 0/3 pointsduffy_ep_ch19_p59 [ ] A single-turn rectangular wire loop measures 6.00 cm wide by 10.0 cm long. The loop carries a current of 2.00 A. The loop is in a uniform magnetic field with B = T. Taking torques about an axis, parallel to either side of the rectangular loop, that maximizes the torque, what is the magnitude of the torque exerted by the field on the loop if the direction of the magnetic field is... (a) parallel to the short sides of the loop? 7.2e-05 N m (b) parallel to the long sides of the loop? 7.2e-05 N m (c) perpendicular to the plane of the loop? 0 N m 2. 0/4 pointsduffy_ep_ch20_p101 [ ]

2 2 of 7 3/13/2010 8:47 AM The picture above shows four different cases of a conducting square loop (in orange), traveling at speed v and passing through a rectangular region. In the left half of the rectangular region, the magnetic field is uniform and directed into the screen; in the right half, the magnetic field is uniform and directed out of the screen. The field has the same magnitude in each half of the rectangular region, and there is no magnetic field outside the rectangular region. (a) Rank the four cases based on the magnitude of the total magnetic flux passing through the loop, from largest to smallest, at the instant shown in the picture. Use only > or = signs in your answer, such as B>A=D>C. B>D>A=C -or- B>D>C=A (b) Rank the four cases based on the magnitude of their induced current, from largest to smallest, at the instant shown in the picture. Use only > or = signs in your answer, such as B>A=D>C. A>D>B=C -or- A>D>C=B (c) Choose the four correct statements, from the list below, regarding the direction of the induced current in each case, at the instant shown in the picture above. There is no induced current in case A. The induced current in case A is directed clockwise. The induced current in case A is directed There is no induced current in case B. The induced current in case B is directed clockwise. The induced current in case B is directed There is no induced current in case C. The induced current in case C is directed clockwise. The induced current in case C is directed There is no induced current in case D.

3 3 of 7 3/13/2010 8:47 AM The induced current in case D is directed clockwise. The induced current in case D is directed (d) Let's say that the square loop measures 20.0 cm by 20.0 cm; that the resistance of the loop is 10.0 ohms; that the speed of the loop is v = 4.00 m/s; and that the magnitude of the magnetic field on each side of the rectangular region is 4.00 T. Calculate the magnitude of the induced current in the loop at the instant shown in case D above A 3. 0/2 pointswiley Simulation [294175] Electromagnetic Induction In this simulation the current in a long straight wire produces a magnetic field. Depending on what is happening to the current in that wire, there may or may not be a current induced in the conducting loop shown to the right of the wire. An ammeter measures the current in the loop. Try moving the slider, which controls the current in the wire, to see what happens to the current in the loop. (a) The current in the loop is sometimes positive and sometimes negative. Under what condition is the current in the loop a positive value? When the magnetic field produced by the long straight wire is directed out of the screen when it passes through the loop. When the magnetic field produced by the long straight wire is directed into the screen when it passes through the loop. When the current in the loop is clockwise. When the current in the loop is

4 4 of 7 3/13/2010 8:47 AM (b) Which of the following statements about this situation are true? Select all that apply. To produce a positive current in the loop, the current in the wire must be positive. To produce a positive current in the loop, the current in the wire must be negative. To produce a positive current in the loop, the current in the wire must be getting more positive (or less negative). To produce a positive current in the loop, the current in the wire must be getting more negative (or less positive). To produce a current in the loop, the current in the wire must be changing, but it makes no difference how fast the current in the wire changes. To produce a current in the loop, the current in the wire must be changing. The faster the current in the wire changes, the larger the magnitude of the current in the loop. 4. 0/2 pointsduffy_ep_ch20_p103 [ ] The picture on the left, above, shows four conducting loops, labeled A through D, that are moving in the indicated direction near a long straight wire that is carrying a constant current to the right. The picture on the right is a similar situation, except in that picture loops E and F are at rest and the current is decreasing in magnitude. (a) In which loops is the induced current directed clockwise? Select all that apply. Loop A Loop B Loop C Loop D Loop E Loop F (b) In which loops is the induced current directed counter-clockwise? Select all that apply. Loop A

5 5 of 7 3/13/2010 8:47 AM Loop B Loop C Loop D Loop E Loop F 5. 0/5 pointsduffy_ep_ch20_p102 [ ] A flat coil of wire, consisting of 20 circular loops with a total resistance of 20.0 ohms, is placed so that it is at rest, flat on a table. The graphs above show the magnetic flux through each loop of the coil as a function of time, for three different cases. The units of flux are webers, which are equivalent to tesla meters 2. The flux through each loop changes because the magnetic field changes. Assume that the field is uniform and the direction of the field is perpendicular to the plane of the coil - positive flux means the field is passing in one direction through the coil, and negative flux means that the field is passing through the coil in the opposite direction. (a) Rank the cases based on the magnitude of the flux passing through each loop of the coil at a time of t = 23 s, from largest to smallest. Only use > and/or = signs in your answer, such as A>B>C. C>A>B (b) Rank the cases based on the magnitude of the induced current in the coil at a time of t = 23 s, from largest to smallest. Only use > and/or = signs in your answer, such as A>B>C. A=B>C -or- B=A>C (c) In Case C, calculate the magnitude of the induced current in the loop at t = 9 s A (d) In Case C, calculate the magnitude of the induced current in the loop at t = 17.5 s A (e) Let's say that, at t = 12 s in case A, the induced current is directed clockwise around the loops in the coil. The induced current should also be directed clockwise at which of the following times and cases? Select all the apply. The induced current is also directed clockwise at...

6 6 of 7 3/13/2010 8:47 AM t = 6 s in Case A t = 22 s in Case A t = 3 s in Case B t = 6 s in Case B t = 17 s in Case B t = 22 s in Case B t = 3 s in Case C t = 6 s in Case C t = 17 s in Case C t = 22 s in Case C 6. 0/2 pointsduffy_ep_ch20_p28 [ ] (a) A Boeing 747 has a wingspan of 64 m. If the jet is flying north at a speed of 750 km/h in a region where the vertical component of the Earth s magnetic field is 4.20 x 10-5 T, directed down, what is the magnitude of the motional emf measured from wingtip to wingtip? 0.56 V (b) Which wingtip is at a higher potential? The east-most wingtip. The west-most wingtip. 7. 0/2 pointsduffy_ep_ch20_p44 [ ] A square loop consists of a single turn with a resistance of 6.00 ohms. The loop has an area of 300 cm 2, and has a uniform magnetic field passing through it that is directed out of the page. The loop contains a 12-volt battery, connected as shown in the figure above.

7 7 of 7 3/13/2010 8:47 AM (a) At the instant shown in the figure, there is no net current in the loop. At what rate is the magnetic field changing? Use a positive sign if the field is increasing and magnitude, and a negative sign if the field is decreasing in magnitude T/s (b) If the polarity of the battery was reversed, and the magnetic field was still changing at the rate you calculated above, what would the magnitude of the net current through the loop be? 4 A Assignment Details