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Unformatted text preview: zzIyer, Savi V Section 99 Physics 125, Analytical Physics II Exam 3 Date Thr, Apr 17, 2008 at 21:00 1. [4pt] A charged particle is moving in a uniform, constant magnetic field. Which of the following statements concerning the magnetic force exerted on the particle is FALSE? A) It might change the velocity of the particle. B) It does no work on the particle. C) It does not change the kinetic energy of the particle. D) It might change the speed of the particle. E) It can act only on a particle in motion. 2. [5pt] For each statement, indicate T-True or F-False. If the first is T and the rest F, write TFFFF. A) In a Hall effect experiment, the electric and magnetic forces on the charge carriers are mutually perpendicular. B) Current density J is a vector. C) The current and electric field in a conductor both point in the same direction. D) The drift velocity of electrons in a typical conductor for currents of the order of 1 A is a few mm / s. E) A 6 m length of copper wire has a resistivity of 1.7 μ Ω · cm. The wire is cut in half. The resistivity of the wire is doubled. 3. [5pt] In a certain mass spectrograph, an ion beam passes un- deflected through mutually perpendicular fields of magnitudes E and B. The beam then enters a region of another magnetic field B’ perpendicular to the beam. The radius of curvature of the resulting ion beam is proportional to: A) B ′ BE B) B B ′ E C) EB ′ B D) BB ′ E E) E BB ′ F) EB B ′ 4. [4pt] Two long straight current-carrying parallel wires cross the x-axis and carry currents i and 3 i in the same direction, as shown. At what value of x (in m) other than infinity is the net magnetic field zero? (If there is no such point on the x-axis check ”not possible”.) 1 3 4 5 7 A) 1.0 B) 3.0 C) not possible...
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