104 Physics Exam 2
March 17, 2005
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 6--25.
1. A 2. C 3. B 4. E 5. D 6. A copper wire of length 25 cm is in a magnetic field of 0.20 T. If it has a mass of 10 g, what is the minimum current through the wire that would cause a magnetic force equal to its weight? (standard free-fall acceleration g = 9.8 m/s2) a. 1.3 A b. 1.5 A c. 2.0 A d. 4.9 A e. 3.6 A 7. Two parallel conductors each of 0.50 m length, separated by 5.0 10-3 m and carrying 3.0 A in opposite directions, will experience what type and magnitude of mutual force? (magnetic permeability in empty space 0 = 4 10-7 Tm/A) a. repulsive, 1.8 10-4 N b. repulsive, 0.60 10-4 N c. attractive, 1.8 10-4 N d. attractive, 0.06 10-4 N e. there is a force only if the conductors have a net charge.
8. The electric field of a point charge decreases inversely as the square of the distance from the charge. The magnetic field of a straight-line current decreases inversely as the first power of the distance from the wire. This difference occurs because a. magnetic field lines never terminate on a pole the way electric field lines do b. the charge is a point source whereas the current is an extended line source c. the magnetic force obeys a right hand rule whereas the electric force is in the direction of the field d. magnetic fields are created only if charge is moving whereas electric fields are created by stationary charge e. electric and magnetic fields are fundamentally different from one another and not linked in any way. 9. An electron moves in a circle inside a solenoid. The plane of the circle is perpendicular to the axis of the solenoid. The solenoid is 20 cm long, its radius is 5 cm, it has 1000 turns, and the current is 10 mA. What is the largest possible electron velocity (so it doesn't hit the solenoid)? (0 = 4 10-7 Tm/A, e = 1.60 10-19 C, me = 9.11 10-31
kg)
a. 3 108 m/s
b. 8.83 106 m/s c. 3.51 105 m/s d. 5.62 106 m/s e. 5.52 105 m/s
10. A magnetic field does no work on a charged particle because a. magnetic fields never terminate or originate on a point b. the magnetic force is always perpendicular to the magnetic field direction c. positive work from one part of the particle trajectory is exactly canceled by negative work from another part of the trajectory. d. the magnetic force vanishes if the particle becomes stationary e. the magnetic force is always perpendicular to the particle motion
11. A square coil, enclosing an area with sides 2.0 cm long, is wrapped with 2 500 turns of wire. A uniform magnetic field perpendicular to its plane is turned on and increases to 0.25 T during an interval of 1.0 s. What average voltage is induced in the coil? a. 2.0 V b. 0.12 V c. 0.25 V d. 2.5 V e. 1.2 V
12. By what factor is the self-inductance of an air solenoid changed if its length and number of coil turns are both tripled? a. 1/3 b. 1 c. 6 d. 9 e. 3 13. A 12-V battery is connected in series with a switch, resistor and coil. If the circuit's time constant is 2.0 10-4 s and the final steady current after the switch is closed becomes 1.0 A, what is the value of the inductance? a. 1.2 mH b. 12 mH c. 9.6 mH d. 48 mH e. 2.4 mH 14. A bar magnet is falling through a loop of wire with constant The velocity. south pole enters first. As the magnet leaves the wire, the induced current (as viewed from above): a. is clockwise b. is counterclockwise c. is zero d. is along the length of the magnet e. creates a torque in the wire 15. Two loops of wire are arranged so that a changing current in one will induce a current in the other. If the current in the first is increasing clockwise by 1.0 A every second, the induced current in the second loop will be: a. counterclockwise and increasing b. zero c. clockwise and increasing d. constant e. question cannot be answered unless the orientation of the loops is specified 16. An AC series circuit has 12.0 resistance, 15.00 inductive reactance and 10.00 capacitive reactance. If an effective (rms) emf of 120 V is applied, what is the power output? a. 1540 W b. 1300 W c. 1160 W d. 1200 W e. 1020 W
17. A resistor and capacitor are connected in series with an applied AC voltage source. Separate voltmeter readings across the resistor and capacitor give values of 50 V and 75 V (rms), respectively. What is the effective (rms) voltage of the source? a. 25 V b. 63 V c. 90 V d. 125 V e. 56 V 18. The electric field, E, in an electromagnetic wave is oriented in what direction with respect to its associated magnetic field, B? a. E parallel to B b. E anti-parallel to B c. E at a 45 angle to B d. E perpendicular to B e. E can be oriented at a variety of angles, provided it has a nonvanishing component perpendicular to B 19. A series RLC circuit in a radio is in resonance with AM 600 kHz. If the radio station is changed to AM 1 200 kHz, by what factor must the capacitance be multiplied to again achieve resonance? a. 4 b. 1/4 c. 1/2 d. 2 e. to achieve resonance both capacitance and inductance must be changed 20. A transformer is to be designed to increase the 30-kV (rms) output of a generator to the transmission line voltage of 345 kV (rms). If the primary winding has 80 turns, how many turns must the secondary have? a. 6 b. 920 c. 70 d. 9 200 e. 129 21. A certain kind of glass has nblue = 1.650 for blue light and nred = 1.610 for red light. If a beam of white light (containing all colors) is incident at an angle of 30.0, what is the...