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PHY 102 Exam #2 Problem 1 2 3 4 Total Instructions: 1. 2. 3. 4. 5. Name ____________ ______________ Points 8 11 18 13 50 Score Do all of your work in this booklet. Show all of your steps in problems for full credit. Be clear and neat in your work. Any illegible work, or scribbling in the margins, will not be graded. Place your answers in a box. If you need more space, you may use the back of the page and write On back in the problem space. 1. Multiple choice (8 pts) Find the answer which best fits the question and write it in the space provided. a. Two long parallel wires have current moving in opposite directions but perpendicular to your paper. The force on the left wire points a) to the left. b) to the right. c) downward. d) none of these. _____ b. In a transformer the voltage in the secondary coil is greater than that in the primary coil. This is a) a step-up transformer; b) a step-down transformer; c) a gobot transformer d) an efficient transformer e) none of these. _____ c. The earth's magnetic field is parallel to the earth's surface at a) the North Pole; b) the South Pole; c) the equator; d) Wilmington, NC, e) none of these. _____ d. The impedance has units of a) farads; b) hertz; c) ohms; d) henries e) none of these _____ e. If the B-field points out of your paper and a negative charge moves from right to left in this field, then the force is directed a) towards the bottom; b) out of the paper; c) into the paper; d) to the left; e) none of these. _____ f. An inductor stores a) electrical energy; b) magnetic energy; c) thermal energy; d) no energy; e) none of these. _____ g. In a capacitive circuit the voltage _________ the current. a) leads; b) is in phase with; c) lags _____ h. A current carrying wire is perpendicular to your paper with the current going into the paper from above. The magnetic field produced looks like a) a uniform field directed from left to right; b) a uniform field directed from right to left; c) concentric circles directed counterclockwise in the plane of the paper; d) concentric circles directed clockwise in the plane of the paper; e) none of these. _____ ___________________________________________________ . 10 31 kg mp 1.67 1026 kg Constants me 911 2. Definitions/Principles (11 pts) a. Write the exact expression for the: (i) the magnetic field inside a solenoid, (ii) the maximum emf generated by a loop rotating in a magnetic field, (iii) the inductive reactance. b. A voltage source of V 12.0sin(120t ) is connected to a 3.0 resistor. Find the (i) Frequency of the voltage source: ____________ (ii) Measured current across the resistor: ____________ c. Indicate the direction of the magnetic field at the center of the solenoid. d. What is the path of the electron? _________________________________________________ Bonus: An LC circuit has a capacitance of 1.5 F and an inductance of 3.0 mH. What is the resonant frequency of this circuit? PHY 102 Exam #2 Name ____________ ______________ 3. Problems (18 pts) a. On the same bar of iron are wound two coils, one with 45 loops and the other with 15 loops. If a 100.0 V alternating voltage is connected to the 45 loop coil, what will be the voltage in the 15 loop coil? 4. Problems (13 pts) a. A series LRC circuit includes a resistance of 150 an inductive reactance of 337 and a capacitive reactance of 293. The rms current in the circuit is 0.233 A. What is the rms voltage of the generator? b. An ionized deuteron (a particle with a +1 charge) passes through a velocity selector with fields of magnitude 40 mT and 8.0 kV/m. Find the speed of the ion. b. In the last part, determine the phase difference and state if the current leads or lags the voltage. c. A magnetic field perpendicular to the plane of a wire loop with and area of 0.40 m2 decreases by 0.20 T in 10-3 s. What is the magnitude of the average value of the emf induced in the loop? c. A 1.0 m long conducting rod is moving perpendicular to a 0.35 T magnetic field. How fast must the rod move in order to produce and emf of 12 V across the ends? d. A proton moves at a speed of 6 106 m/s perpendicular to a constant magnetic field. The path is a circle of radius 1.3 103 m. What is the magnitude of the magnetic field? d. What voltage is needed to create a current of 29.0 A in a circuit containing only a 0.565 mF capacitor, when the frequency of the source is 2.60 kHz? e. In the figures below indicate the direction (left or right) of the induced current along the path between points a and b. e. An electric power line carries a current of 1400 A in a location where the earth's magnetic field is 0.5 G. The line makes an angle of 75o with respect to the field. What is the magnitude of the magnetic force on a 120 m length of line? __________ (when switch closed) f. What is the current in a long, straight wire if the magnetic field 1.00 mm from the wire is 2.00 102 T? __________ __________