Physics 202 – Second Exam February 27, 2007 Ignore the sign of the answer. Answer ‘e’ is to be used as ‘none of the above’, ‘cannot be answered’, etc You may not have a cell phone or any electronic device (other than a non-programmable calculator with one memory and two pencils at your desk during the exam. You may not have any paper even blank or notes at your seat. You are to take your test questions home with you and only submit your answer sheets. The +z direction is out of the paper toward your face and +x is to your right, +y up the page. 1. What is the numerical value of o? a. o b. ~ 4E-7 c. 1/o d. 4 2. The equation that gives the force on an electric charge moving in a magnetic field is associated with what name? a. Biot & Savart b. Faraday c. ~ Lorentz d. Ampere 3. The equation that is associated with the magnetic field generated by a segment of current is associated with what name(s)? a. Faraday b. Lorentz c. Gauss d. ~ Biot Savart e. Einstein 4. Whose equation enables one to compute the magnetic field for highly symmetric cases as one can do for the electric field using Gauss’ law of electric fields? a. ~ Ampere b. Gauss c. Faraday d. Lorentz 5. A loop of wire is in the xy plane in a circle of radius 2 m and carries a current of 7 Amps moving from the +x to the +y axis directions. What is the magnetic moment of this loop? a. 14 b. 56 c. ~ 28 d. 2 6. What is the direction of the magnetic moment? a. - z b. ~ + z c. +y d. -y 7. What is the torque on this magnetic dipole in a magnetic field B=5 at an angle away from the dipole of 25 degrees. a. 168 b. 137 c. 141 d. ~ 186 8. If a sphere of radius 4.4m surrounds this dipole, what is the total flux through the cube? a. ~ 0 b. 4.4 c. 2 d. 1/ (4.4 9. If an infinite straight wire is horizontal directly in front of you and carries a current of 9 Amps flowing from your right to your left (-x direction), then what is the magnetic field at the end of your nose which is 4 meters away from the wire. a. 5.4E-7 b. 2.3E-6 c. ~ 4.5E-7 d. 7.6E-7 1 10. What is the direction of the magnetic field at your nose. a. –y (downward on your face) b. ~ +y (upward on your face) c. –x (left) d. x (right) 11. If a 2 m segment of wire carries a current of 8 Amps at an angle of 50 degrees from a magnetic field of B= 4, then what is the force on the segment. (Assume that the current goes away from the place where it crosses the magnetic field. a. 0 b. 64 c. 46 d. ~49 12. If a negative charge is moving to your right (+x direction) and a magnetic field is coming out of the test page toward your face (+Z) then what is the direction of the force. a. –y (down the page) b. ~ +y (up the page) c. –x (left) d. x (right) 13. Imagine you are in a room with a uniform magnetic field of 10 T toward the front of the room. There is a rectangle of wire (one strand) measuring 2 m by 7 m at an angle of 35 degrees (for its normal) with the magnetic field. What is the flux through the loop? a. 140 b. 1/140 c. ~115 d. 0 14. If this coil turns at a rate where the angle increases to 90 degrees in 8 seconds, then what is the emf generated by the system? a. 1.244 b. 3.87 c. 38.77 d. ~ 14.3 15. Whose law is applicable to this last problem? a. ~ Faraday’s b. Amperes Gauss d. Henry c. 16. What is the value the reciprocal of the square root of the product of o and o? a. 1/c b. 1 c. ~ c d. 1E-7 17. Which of the following has the shortest wave length? a. ~ blue b. orange short wave radio d. microwaves c. 18. If an inductor of 6 Henries, with a square cross section of 4 m2, has a current of 36 Amps change to 16 Amps in a time of 2 seconds, then what voltage results from this change? a. ~ 60 b. 30 c. 120 d. 0 19. How much energy was originally stored in the inductor? a. 4.977 b. 12,040 c. ~ 3888 d. 2111 20. A transformer has an input of 6 amps and 18 volts on the input side with 100 turns and the output side has 400 turns. What is the output voltage? a. 18 b. ~ 72 c. 36 d. 64 21. What is the output current in amps? a. ~ 1.5 b. 72 2 c. 14 d. 36 22. What is the output power? a. 36 b. 0 c. 4.45 d. ~ 108 23. Compute using the first two terms: sin(.25) ? a. ~ 0.2474 b. 0.2495 0.247404 d. 0.26 c. 24. Which of the ‘Maxwell equations’ was modified by Maxwell? ? a. Gauss b. Faraday c. Lenz d. ~ Ampere 25. In a comparison between the harmonic oscillator and the RLC circuit, what does C correspond to in the mechanical equation? a. k b. ~ 1/k c. m d. 1/m 26. If such a system has an extremely small R, then it would be called a. overdamped b. critically damped c. ~underdamped d. infinitely damped Answer the following for green light which has a frequency of 6E-14 27. What is its period? a. 2E-14 b. 1.8E-14 c. 3.6E-15 d. ~ 1.67E-15 28. What is its angular frequency? a. ~ 3.77E15 b. 4.77E15 c. 4.2E13 d. 3.88E15 29. What is its wave number? a. 1.944E8 b. 1.944E7 c. ~ 1.26E7 d. 1.9E5 30. What is its wave length? a. ~ 5E-7 b. 7E-5 c. 6E-6 d. 7E-7 31. If its maximum magnetic field is 3E-4 T then what is the maximum electric field? a. 30,000 b. 10,000 c. 2.7E5 d. ~ 90,000 32. What is the ratio of the energy stored in its electric to its magnetic field? a. 0 ~ 1 c. 2 d. 1/2 3 b.