PHYS 272/fall2015: Assignment EXAM02FALL15

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1 PHYS 272/fall2015: Assignment EXAM02FALL15 User: avina For user = avina (14knqt10425 overriding avina for randomization) Logout f15ex02q03 [7 points] (Last updated: Thu Oct 29 08:45: ) [avina] Current carrying loops The figure shows various configurations of current-carrying wires. Each wire carries the same current, and all circles and semicircles are centered on the origin. The large circles and semicircles have radius R = 6 m. The small ones have radius r = 3 m. Which statement is true about the magnitude of the magnetic field at the origin in each case? You may neglect the small contribution to the magnetic field at the origin due to the straight segments of wire. a. B 2 < B 1 < B 3 b. B 1 < B 2 < B 3 c. B 2 = B 3 < B 1 d. B 3 < B 1 = B 2 e. B 1 = B 2 < B 3 Page 1 of 9

2 f15ex02q04 [7 points] (Last updated: Fri Oct 30 09:43: ) [avina] Magnetic field due to a moving electron An electron moves in the +y direction, as shown in the figure. What is the direction of the magnetic field at location D in the x-y plane, due to the electron? a. +z b. +x c. -z d. +y e. -x f15ex02q05 [7 points] (Last updated: Thu Oct 29 12:44: ) [avina] Electric current in copper The electron mobility in copper is C.m/N.s, and the density of the mobile electrons is m -3. In a copper wire, 1 mm in diameter, there is an electric field whose magnitude is 0.05 N/C. What is the conventional current in this wire? a A b A c A Page 2 of 9

d. 1.24 A e. 4.74 A f15ex02q02 [7 points] (Last updated: Thu Oct 29 08:45:07 2015) [avina] Two connected wires In a circuit in steady state, current is flowing from the thick wire into the thin wire.

3 d A e A f15ex02q02 [7 points] (Last updated: Thu Oct 29 08:45: ) [avina] Two connected wires In a circuit in steady state, current is flowing from the thick wire into the thin wire. Both wires are made from the same material. E thick is the electric field in the thick part of the wire, and E thin is the electric field in the thin part of the wire. If the diameter of the thin wire is 1/4 the diameter of the thick wire, which of the following is true about the electric fields? a. E thick = (1/4)E thin b. E thick = E thin c. E thick = (1/16)E thin d. E thick = 4 E thin e. E thick = 16 E thin f15ex02q06 [7 points] (Last updated: Thu Oct 29 08:48: ) [avina] Circuit with wires The circuit shown in Figure below consists of a single battery whose emf is 1.8 V, and three wires made of the same material, but having different cross-sectional areas. Each thick wire has a cross-sectional area of m 2 and is 25 cm long. The thin wire has a cross-sectional area m 2 and is 6.1 cm long. solve Page 3 of 9

4 for the magnitudes of electric fields E D and E F at locations D and F a. E D = V/m; E F = V/m b. E D = V/m; E F = V/m c. E D = 21.9 V/m; E F = V/m d. E D = 21.9 V/m; E F = V/m e. E D = V/m; E F = V/m f15ex02q07 [7 points] (Last updated: Fri Oct 30 09:02: ) [avina] Potential energy in a circuit The figure below shows the potential difference in a circuit consisting of two thick wires, a highly resistive thin wire and a battery. Page 4 of 9

5 Which figure below shows the correct electric potential energy of a conduction electron for the above circuit? a. b. c. Page 5 of 9

6 d. f15ex02q08 [7 points] (Last updated: Thu Oct 29 08:49: ) [avina] Current through a glowing bulb The conductivity of tungsten at room temperature, = (A/m 2 )/(V/m), is significantly smaller than that of copper. At the very high temperature of a glowing light-bulb filament (nearly 3000 degrees Kelvin!), the conductivity of tungsten is 18 times smaller than it is at room temperature. The tungsten filament of one of your round bulbs has a radius of about 0.02 mm. Calculate the magnitude of the electric field required to drive 0.39 amperes of current through the glowing bulb. a V/m b V/m c V/m d V/m e. 310 V/m f15ex02q01 [7 points] (Last updated: Fri Oct 30 09:42: ) [avina] Magnetic field due to a current Page 6 of 9

7 The coil in the figure is connected to batteries which are not shown. Conventional current runs through the coil in the direction shown. Select the direction that best corresponds to the direction of the magnetic field at location A, due to the current in the coil. a. +z b. +x c. -z d. +y e. -x f15ex02q09 [7 points] (Last updated: Thu Oct 29 08:50: ) [avina] Two nichrome wires The circuit shown below consists of two flashlight batteries and two nichrome wires of different lengths and different thicknesses as shown. The thin wire ( wire number 1) is 50 cm long, and its diameter is 0.25 mm. The thick wire (wire number 2) is 15 cm long, and its diameter is 0.35 mm. The emf of each flashlight battery is 1.5 volts. Determine the steady-state electric field inside each nichrome wire. Page 7 of 9

8 a. E 1 =5.20 V/m; E 2 =2.65 V/m b. E 1 =2.65 V/m; E 2 =5.20 V/m c. E 1 =2.24 V/m; E 2 =4.40 V/m d. E 1 =1.68 V/m; E 2 =3.76 V/m e. E 1 =3.76 V/m; E 2 =1.68 V/m f15ex02q10 [7 points] (Last updated: Thu Oct 29 08:50: ) [avina] Wire on compass You place a long straight wire on top of your compass, and the wire is a height of 5 mm above the compass needle. If the conventional current in the wire is I= 0.2 ampere and runs left to right as shown, calculate the approximate angle the needle deflects away from north. The magnetic field of the Earth at the location is T. a. 31 b. 41 c. 22 d. 18 Page 8 of 9

9 e. 8 Logout CHIP ID: avina Page 9 of 9

Resistance and Ohm s Law R V I. 1 ohm = 1 volt ampere

Resistance and Ohm s Law R V I. 1 ohm = 1 volt ampere Resistance and Ohm s Law If you maintain an electric potential difference, or voltage V, across any conductor, an electric current occurs. In general, the magnitude of the current depends on the potential