exam 2 sol - PHY 1033 Fall 2010 Exam #2/Solutions Ihas Oct....

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Unformatted text preview: PHY 1033 Fall 2010 Exam #2/Solutions Ihas Oct. 19 You are allowed to consult one 8.5”x11” sheet of paper with anyt hing written on it in your own hand, and to use a calculator, ruler, and pencils or pens. Number your answer to each q uestion clearly, answering them in numerical order in a “Blue/Green Book” test form. If your exam book had enough p ages left ion it from the last exam, you may use it. Clearly put your name on the front of the blue/green book with “E xam #2” and today’s date. Do not violate the UF honor code. Write on the front of the blue/green book “I have neith er given nor received help from anyone during this exam”, and sign your name. Answers without the required justifica tion or explanations will be counted wrong, even if they are correct. You may quietly ask me any question after raising y our hand, but my answers will only clarify the exam questions. Good luck! c = 3x108 m/s n(water) = 1.33 1. Regarding electrons, what is the difference between a c onductor and an insulator? Conductor has a free electrons which can easily move. 2. What field or fields, if any, compose an electromagnetic wave? Electric and Magnetic. 3. Does a changing magnetic flux always produce an induc ed field, or only if there is a conductor present? Always. 4. Microwaves get their name from their wavelength, whic h is about 1/1,000,000 meter. What is the frequency of such a light wave? You now know this was a lie, but given the bogus wavelength, the answer would be f = c/λ = 3x108 m/s / 1x10‐6 m = 3x10‐14 /s = 3x1014 Hz. 5. Do microwaves oscillate at a higher or low frequency th an visible light? Lower. 6. If a pulse of the waves in problem # 4 lasts 10‐10 sec, how many wavelengths are in it? N = f x Δt = 3x1014 Hz x 10‐10 s = 3x104 . 7. How long in space is the wave train in problem #6? L = λ x N = 10‐6 m x 3x104 = 3x10‐2m = 0.03 m. 8. What physically changes in a light wave which enters a block of clear glass? Speed and wavelength; p NOT frequency. 9. Light from the sun falls on a linear Polaroid, and then pa sses through another linear Polaroid rotated 90° to the first Polaroid. How much of the original sunlig gets through both Polaroid’s? None—Zero. ght 10. Two light waves (red and blue) bend on going through a slit and then again on going through a prism of glass. Is it possible for them to make a bright spot on a s screen in the same place, or is this impossible? Explain. Since the beam experiences two effects which have opposi dependences on wavelength, it ite is possible. As they go thru the slit, the red would bend more than the blue, but on going thru the prism, the blue would bend more than the red, making i t possible, by proper positing of the slit, the prism, and the screen to bring the different color beams back together on a screen. 11. A charged particle is stationary in a magnetic field B. W hat force does it feel from this field? None. It is stationary relative to the field. 12. An electric current is flowing in a positive direction in a vertical wire. Use your right hand to determine what the magnetic field produced looks lik e and draw it in a picture, showing w the direction of the flux. 13. The figure shows a situation involving Faraday’s Law. If we flip the bar magnet around so the S pole is to the le and we eft, move our hand AWAY from the coil of wire (moving to t he right), what else, if anything, will change in the picture and why? Nothing else changes, since the CHANGE in flux will be the same. 14. What is Brewster’s angle for light reflection off a clear lake? tanӨ = n = 1.33 so Ө = Inverse (tan 1.33) = 53° 15. Which pole of the Earth’s magnet is near the north geographic pole? South. 16. Why does putting two polarizers oriented at right angles to each other in front of each slit in Young’s interference experiment prevent the interference pattern from being seen? Each slit then passes light of opposite polarization, which means the light from each slit is coming from different atoms. Only a single photon, coming from one atom, can interfere with itself—only then is there coherence. 17. When electrical charges move in solid substances they are usually electrons? The following 2 questions (#18 & #19) refer to a hollow metal (conducting) spherical shell which has a net negative electrical charge: 18. What is the electric field configuration INSIDE the shell (draw a picture if you like). Zero—no field inside a conductor. 19. What is the electric field configuration OUTSIDE the shell (draw a picture if you like). Radial pointing towards the center of the sphere. 20. Does a changing magnetic flux produce an electric current if there is no conductor present? Explain. No, there must be an electrically conducting circuit to carry the flow of electrons. ...
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This document was uploaded on 05/29/2011.

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