Assignment_8_09_v4

Assignment_8_09_v4 - TA's Name_Section Your Name Physics...

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TA's Name:_____________________________________Section: ____ Your Name: ____________________________________ Physics 2214 Assignment 8 Concepts: EM Waves - relations between E, B and v Polarization by reflection, Brewster's angle Plane waves Polarization Reflection, Refraction of EM waves Snell's law Total internal reflection Reading: Y&F, Vol. 2, Chapters 32 and 33 Assignment: Due in lecture on Thursday, March 26. Please turn in this sheet stapled to the top of your work. Physics Problems: 1. Where do electromagnetic waves come from? Let's consider a charge Q at the origin x=0, y=0, and a point at a distance x 1 along the +x axis. (a) Draw the charge Q and a vector showing the direction of the electric field at x 1 . (b) On the same graph, draw the direction of the electric field at x 1 when the charge Q is at x=0, y=y 1 . If x 1 is large compared with y 1 , how does the magnitude of the x component of E G compare with (i) its y component and (ii) the magnitude of the x component in (a)? (c) Suppose that the charge Q is displaced from x=0, y=0 to x=0, y= y 1 at t=0. Sketch E x (x 1, t) and E y (x 1, t), again assuming that x 1 is large compared with y 1 . (You don't have to indicate the magnitude of E, just the shape.) (d) Now suppose that you oscillate the y position of the charge Q according to y(t)= y 1 cos( ω t). Sketch E y (x 1, t) now. (e) For the oscillating charge in (f), in what direction does the magnetic field point at x=x 1 ? Hint: the oscillating charge produces a current. From Ampere's law in integral form, in what direction would you expect the magnetic field at x=x 1 produced by this current to point? (In fact, these arguments focusing on the electric field produced by the charge and the magnetic field produced by the current don't give the whole picture. We're neglecting the magnetic field produced by the time varying electric field, and the electric field produced by the time varying magnetic field.) 2. TV Ghosting. Y&F, Chapter 32, Exercise 32.2. Similar "ghosting" can happen with AM and FM radio signals. Ghosting can also occur in transmission of signals down coax, fiber or waveguide, where the reflections arise at discontinuities, often associated with bad connectors or a kink or other damage to the cable. I've often seen ghosting in

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Assignment_8_09_v4 - TA's Name_Section Your Name Physics...

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