Physics 307 Homework
 RU Links   Radford University   Department of Physics   RU Planetarium   RUSMART pages (weather) Spring 2013 Classes & Info   PHYS 112   PHYS 307   PHYS/GEOL 406   My daily schedule   My C.V. Summer jobs/internships   NSF REU Program (list of REU sites) Other links   The Nucleus (resources for    physics/astronomy undergrads)   Pre-Health information   R.U.F.R.E.E.Z.I.N.G.    pics from the north pole trip    the picture from the trip   Simple 2-liter water rocket   American Institute of Physics Homework #2: Due Saturday, February 9 by 10:00am. Note that there is a test on the material up to this point. We will have the test in the lab on Tuesday, February 12 (you take your test during your regular lab time). Important note: While there is only one type of, say, the first problem below, you should be able to work each of these problems in general. For example, what if I would ask you for the energy required to bring perhaps 3 charges together in a line, or even a triangle? You should always work all homework problems with the thought in your mind, "How might this be reworded to make a problem with the same concept, but a different physical situation?" Find the energy required to bring 4 identical charges together in a line, with each one separated by 2.0A ("A"="angstrom"=10-10m). Each charge has a magnitude of (+)2e (e=1.602x10-19C). The example Mathematica worksheet in the class web page will be helpful with this. Plot both the electric field vectors and the electric field unit vectors due to a +4,000e charge located at the point (x,y)=(.90m, 1.30m). You are to plot this in the range x=-4.0m to 4.0m and y=4.0m to 4.0m. I would be glad to check your program before you turn it in. A coaxial cable is shown below. The radius of the inner conducting wire is 0.50mm; the radius of the outer wire is 3.50mm. The entire cable is 2.50m long. There is a charge of (+)2.20μC on the inner wire and a charge of (-)4.5μC on the outer wire. (Recall that all charges will scurry to the surface of conductors, eliminating electric fields inside the metal of those conductors.) Assuming you are relatively far from the ends of the wire, find the magnitude of the electric field at a radius of (a) 0.25mm, (b) 1.10mm and (c) 4.70mm. Find the electric field (magnitude and direction) at the field point (xf,yf)=(7cm, 11cm) due to a rod that lies along the x-axis from x=(-)30cm to x=(+)25cm. Thus, this rod is not " infinitely long." The linear charge density is given by λ=(-)2.0μC/m. Personally I find Mathematica really helpful in doing such integrals, or maybe Wolfram Alpha.    That's all for homework #2.