Unformatted text preview: Exam 4 – white version Physics 2760 SP 2008 Last Name______________________________ First Name_____________________________ ID # ___________________ This is a closed book exam. I understand, pursuant to University Regulations on academic honesty, that I am not to use any notes or information other than what is in the official, non‐annotated formula sheet. Signature_______________________________________ For multiple choice questions, please make sure that you circle the letter for the answer which you believe to be correct and only that answer. If more than one answer is circled for the same problem, you will not receive credit for it. Don’t get hung up on questions. And just because Cody asked for it, the correct answer for question two is d. They should take only one or two minutes each. If you find yourself spending more than a few minutes on a multiple choice question you are probably looking at it the wrong way. You should skip it for now and come back to it later. For full credit show your work for solutions to questions that require calculations. Explain from where you start to solve the problem and show your math flowing from it for full credit. No shown work, no credit! Relax, read carefully, think – and then read everything again. During the exam, if you have questions please raise your hand and the TA or the instructor will come to you and provide help. 1. The theoretical upper limit for the frequency of electromagnetic waves is: A) just slightly greater than that of red light B) just slightly less than that of blue light C) the greatest x‐ray frequency D) none of the above (there is no upper limit) E) none of the above (but there is an upper limit) 2. The electric field E of an electromagnetic wave traveling the positive x direction is illustrated in the figure. This is the wave of the radiation field of an antenna. What is the direction and the phase relative to the electric field of the magnetic field at a point where the electric field is in the negative y direction? Note: The wave is shown in a region of space that is a large distance from its source. a) +y direction, in phase b) −z direction, 90° out of phase c) +z direction, 90° out of phase d) −z direction, in phase e) +z direction, in phase 3. Which one of the following statements about light is accurate? A) Total internal reflection can occur only for light passing from an optically dense (large n) medium to an optically rare (small n) medium. B) For angles of incidence less than the critical angle, all the light is absorbed in the second medium. C) Total internal reflection can occur only for light passing from an optically rare (small n) medium to an optically dense (large n) medium. D) Total internal reflection can occur for light traveling either way across a boundary. E) For angles of incidence greater than the critical angle, all the light is absorbed in the second medium. 4. A beam of light travels from air into a sheet of glass having refractive index n. Which one of the following statements about this light is accurate? A) If we increase the angle of incidence, the angle of refraction decreases. B) If we increase n, the angle of incidence decreases. C) The angle of refraction will be greater than the angle of incidence. D) If the angle of incidence is large enough, the light will be totally reflected back into the air. E) If we double the angle of incidence, the angle of reflection also doubles. 5. The figure shows the path of a portion of a ray of light as it passes through three different materials. Note: The figure is drawn to scale. What can be concluded concerning the refractive indices of these three materials? a) n1 < n2 < n3 b) n2 < n1 < n3 c) n1 > n2 > n3 d) n1 < n3 < n2 e) n3 < n1 < n2 6. In the circuit shown in the figure, ε = 60.0 V, R1 = 30.0 Ω, R2 = 20.0 Ω, and L = 0.294 H. Switch S is closed at t = 0 sec. a) Just after the switch is closed, what is the potential difference vab across the resistor R1? b) Which point, a or b, is at a higher potential? c) What is the potential difference vcd across the inductor L? d) Which point, c or d, is at a higher potential? e) The switch is left closed a long time. What is the current through the inductor after a long time? f) The switch is then opened. Just after the switch is opened what is the potential difference vab across the resistor R1? g) Which point, a or b, is at a higher potential? h) What is the potential difference vcd across the inductor L? i) Which point, c or d, is at a higher potential? 7. A coil is connected to a 60‐Hz, 100‐V AC generator. At this frequency the coil has an impedance of 10 Ω and a reactance of 8 Ω. a) What is the current in the coil? b) What is the resistance of the coil? c) What is the phase angle between the current and the applied voltage? Draw a phase diagram to show how you would find the phase angle. c) What series capacitance is required so that the current and voltage are in phase? d) What is the current through the circuit in this case? e) What is the voltage measured across the capacitor in this case? 8. The switch in the figure below is connected to point a for a long time. The switch is then thrown to point b. A) What is the maximum charge that appears on the capacitor? B) What is the frequency of oscillation of the LC circuit? C) What is the maximum current in the inductor? D) What is the total energy the circuit possesses at t = 3 s? E) At what time is the energy stored in the capacitor equal to the energy stored in the inductor? MC 25/ Q6 25/ Q7 25/ Q8 25/ Total 100/ ...
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- Spring '08
- Physics, Total internal reflection, Q7, potential difference Vab, potential difference Vcd