2212 Physics Fall 2003
Quiz #3 Form #211
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You may use a calculator that cannot store letters and the formul sheet provided, but no other aids. 1. (8 points) When a positively charged particle at a point P has a velocity in the positive y direction, it experiences a magnetic force in the positive z direction. Which one of the following statements is true regarding the magnetic eld, B = Bx + By + Bz k at the point P ? (a) (b) (c) (d) (e) Bx Bx Bx Bx Bx > 0, < 0, < 0, < 0, > 0, By By By By By = 0, and Bz = 0. is undetermined, and Bz is undetermined. is undetermined, and Bz = 0. = 0, and Bz = 0. is undetermined, and Bz = 0.
2. (8 points) A rectangular solid made of carbon has faces of area A, 2A, and 3A, as shown in the scale diagram. How would you connect the wires from a battery to the center of two opposite faces so as to obtain the least current? (a) Since the volume is constant, it doesnt matter which opposite faces the wires are attached to. (b) Since the length matters, the opposite faces to which the wires should be be attached cannot determined from just the areas. (c) Attach the wires to a face of area 2A and the similar face opposite. (d) Attach the wires to a face of area 3A and the similar face opposite. (e) Attach the wires to a face of area A and the similar face opposite.
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3. (10 points) In the illustrated circuit, E = 24 V, R1 = 100 , R2 = 200 , and R3 = 300 . What current does the battery supply? (a) 0.44 A (b) 0.29 A (c) 0.11 A (d) 0.04 A (e) 0.08 A
4. (10 points) The capacitor in the illustrated circuit is initially uncharged. After the switch, S, is closed, how much time does it take for the potential across the resistor to be 30% of the battery voltage? Express your answer in terms of the time constant, . (a) 0.36 (b) 0.70 (c) 0.30 (d) 1.0 (e) 1.2
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5. (10 points) Two ions, each of charge +e, moving perpendicularly to a uniform 0.4 T magnetic eld with speeds of 500 km/s follow circular paths that dier in diameter by 5.0 cm. What is the dierence in the mass of these two ions? (a) (b) (c) (d) (e) 3.2 1027 kg 4.8 1027 kg 9.6 1027 kg 8.0 1027 kg 6.4 1027 kg
6. (10 points) What current must be maintained through a single square loop (50 cm on a side) to create torque a of 1.0 Nm on the loop when placed in a 70 mT magnetic eld oriented such that the angle between the eld and the plane of the loop is 40 ? (a) 89 A (b) 66 A (c) 57 A (d) 61 A (e) 75 A
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7. (10 points) A tellurium (resistivity 4.36 103 m) wire is to be constructed, circular in cross-section and 880 m in length. When a 9.0 V potential dierence is applied between the ends of the wire, not more than 12 mW should be dissipated in the wire. What is the wires maximum radius? (a) 1.9 mm (b) 4.1 mm (c) 8.1 mm (d) 13 mm (e) 22 mm
8. (10 points) A conductor with a mass per unit length of 0.040 kg/m is suspended above the Earth by a horizontal magnetic eld, B. A segment is shown. What current must exist in the conductor if the magnetic eld in the region with the wire is 0.26 T into the page? (a) 0.11 A (b) 1.5 A (c) 6.5 A (d) 38 A (e) 0.67 A
9. (4 points) In the previous problem, in which direction must the current ow? (a) Left to right. (b) Right to left.
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10. (4 points) In a Hall eect experiment, conventional current, i, is owing in the indicated direction through a metal strip in the presence of a uniform magnetic eld, B. The potential dierence is measured between two points, a and b, on opposite edges of the strip. What is the relationship between the potential at point a and that at point b? (a) Va > Vb (b) Vb > Va
11. (8 points) You have a case of ashlight bulbs, each of which will burn out if more that 6 V is applied across it. Your power supply has only one setting: 120 V. Would it be possible to light several of your 6 V bulbs without burning them out, and if so, how? (a) (b) (c) (d) (e) No, it is impossible. Yes, connect 20 bulbs in parallel with the power supply. Yes, connect 20 bulbs in...