104 Physics Exam 2
October 30, 2008
Name__________________________________________ ID #____________________ Section #______________ TA Name_________________________________________ Fill in your name, student ID # (not your social security #), and section # (under ABC of special codes) on the Scantron sheet. Fill in the letters given for the first 5 questions on the Scantron sheet. These letters determine which version of the test you took, and it is very important to get this right. Make sure your exam has questions 625. 1. C 2. E 3. B 4. D 5. A
6. Charged particles flow in a straight line with a constant velocity. Their current is uniformly distributed over a circular area in the plane perpendicular to the motion. The magnetic force on these particles a. is everywhere inward (toward the center of the circle) in the plane perpendicular to the direction of motion. b. is zero because the particles produce a magnetic field that is wholly outside the region of current. c. is zero even though the particles produce a magnetic field in the region of current. d. is in the direction that opposes the current flow. e. is everywhere outward (away from the center of the circle) in the plane perpendicular to the direction of motion.
7. Niobium metal becomes a superconductor (with electrical resistance equal to zero) when cooled below 9 K. If superconductivity is destroyed when the surface magnetic field exceeds 0.100 T, determine the maximum current a 6.00-mm-diameter niobium wire can carry and remain superconducting. (0 = 4 107 Tm/A) a. 187.5 A b. 4 712 A c. 750 A d. 375 A e. 1 500 A
8. A copper wire of length 25 cm is in a magnetic field of 0.20 T. If it has a mass of 20 g, what is the minimum current through the wire that would cause a magnetic force equal to its weight? a. 2.6 A b. 4.0 A c. 3.0 A d. 9.8 A e. 2.0 A
9. A solenoid with 500 turns, 0.10 m long, carrying a current of 42.0 A, and with a radius of 102 m will have what strength magnetic field at its center? (magnetic permeability in empty space 0 = 4 107 Tm/A) a. 16 104 T b. 40 104 T c. 126 104 T d. 62 104 T e. 31 104 T
10. A circular current loop is placed in an external magnetic field. How is the torque related to the radius of the loop? a. directly proportional to radius b. directly proportional to radius squared c. inversely proportional to radius d. does not depend on the radius e. inversely proportional to radius squared
11. A 5-turn square coil of area 0.036 m2 and a 20-turn circular coil are both placed perpendicular to the same changing magnetic field. The voltage induced in each of the coils is the same. What is the area of the circular coil? a. 0.009 m2 b. 0.30 m2 c. 0.018 m2 d. 0.06 m2 e. 0.036 m2
12. A 500-turn circular coil with an area of 0.050 0 m2 is mounted on a rotating frame, which turns at a rate of 20.0 rad/s in the presence of a 0.10 0-T uniform magnetic field that is perpendicular to the axis of rotation. What is the instantaneous emf in the coil at the moment that the normal to its plane is at a 90.0 angle to the field? a. 25.0 V b. 43.2 V c. zero d. 50.0 V e. 500 V
13. A 12-V battery is connected in series with a switch, 12.0- resistor and coil. What energy is stored in the coil when the current is 2.0 A? The time constant is 4.0 104 s. a. 28 103 J b. 19.2 103 J c. 9.6 103 J d. 192 103 J e. 58 103 J
14. In a circuit made up of inductor, resistance, ammeter, battery and switch in at series, which of the following times after the switch is closed is the rate of current increase greatest? a. zero b. one time constant c. ten time constants d. reciprocal of one time constant e. in the limit that the time goes to infinity
15. A coil with a self-inductance of 0.75 mH experiences a constant current buildup from zero to 20 A in 0.25 s. What is the induced emf during this interval? a. 0.090 V b. 0.94 V c. 0.004 V d. 0.038 V e. 0.060 V
16. A resistor, capacitor, and inductor are wired in series with a voltage generator that produces a voltage varying sinusoidally in time with any desired frequency. A certain frequency is called the resonance frequency. This frequency is a. is given by the inductance divided by the resistance. b. is given by the inverse of the product of resistance and capacitance. c. the frequency at which the power dissipated in the resistor is minimum d. the frequency at which the power dissipated in the resistor is maximum. e. the only frequency at which the generator can successfully impose a voltage drop over the other elements of the circuit.
17. What is the impedance of an AC series circuit that is constructed of a 10.0- resistor along with 15.0 inductive reactance and 10.0 capacitive reactance? a. 11.2 b. 27.0 c. 37.0 d. 27.7 e. 125
18. A radio wave signal, which transmits at a frequency of 3.60 MHz, has what wavelength? (c = 3.00 108 m/s) a. 83.3 m b. 57.6 m c. 8.34 m d. 5.76 m e. 4.8 102 m
19. An AC series circuit has 12.0 resistance, 15.00 inductive reactance and 10.00 capacitive reactance. If an effective (rms) emf of 240 V is applied, what is the effective (rms) current value? a. 10.62 A b. 18.46 A c. 1.42 A d. 21.6 A e. 52.0 A
20. Consider an AC series circuit containing a coil, capacitor and resistance. Doubling the frequency will change the inductive reactance by what factor? a. 1/2 b. 4 c. 1.0 d. 1/4 e. 2.0
21. An oil film floats on a water surface. The indices of refraction for water and oil, respectively, are 1.333 and 1.466. If a ray of light is incident on...