Microsoft Word - Quizz 2.docx Physics112 OptionalQuiz2 1 Student Name: Section: Please circle your corresponding section A or B Physics 112 Optional Quiz 2. If you decide to turn in the optional...

Physics Homework


Microsoft Word - Quizz 2.docx Physics112 OptionalQuiz2 1 Student Name: Section: Please circle your corresponding section A or B Physics 112 Optional Quiz 2. If you decide to turn in the optional quiz please do so by bringing it to my office (Ho 410) before 5 PM, March 8th. If I am not in my office please slide it underneath the door. Quizzes turned in late will not be graded. If you are traveling and have already discussed with me regarding emailing a scanned version, please do so before the deadline. Please write solutions on a separate sheet of paper and staple it to this cover page. Do not write the solutions on this page. In order to maximize partial credit, a good idea is to first work out the answer symbolically before plugging in any numbers. This quiz contains 3 problems. 1. Every bit of length of electric current is a source of magnetic field. Think of the field due to each current segment as encircling the segment, as shown at right. a. In the figure at right, in what direction does current flow? If the current were made up of moving electrons in a wire, in what direction are the electrons moving? b. The principle of superposition applies to magnetic fields as well as to electric fields. If we stitch together many bits of current into a loop of current, in what direction will the magnetic field point at the center of the loop? For concreteness, suppose the current circulates counterclockwise around the loop, as viewed from above. c. In what direction would the magnetic field point above, or below, the center of a horizontal loop of current? Again, suppose that the current in the loop circulates counterclockwise as viewed from above. d. In what direction would the magnetic field point at places outside the loop, in the plane of the loop itself? e. We have noted in class that the a current loop constitutes a magnetic dipole. What is the direction of the magnetic dipole moment of the loop in parts (b)-(d)? Compare what you know about the arrangement of the magnetic field above and below the dipole to what you know about the arrangement of the electric field above and below an electric dipole. Physics112 OptionalQuiz2 2 2. A mobile bar lies across two conducting rails that are connected to a light bulb of resistance 240 W, as shown in the figure at right. The rails are 20 cm apart. The entire system lies in a magnetic field of 0.2 T, directed out of the page. You must do work to move the mobile bar. If you try to move it at walking speed (1 m s-1), how much power must you supply? 3. The gyromagnetic ratio of the neutron is If we could immerse a nuclear reactor core (containing many neutrons) in a strong magnetic field of 1 T, what fraction of the neutrons would have their spins aligned with the magnetic field at a temperature of 350 K? Like the electron and the proton, the neutron can only have two possible values of angular momentum along the direction of the magnetic field, (Note: the answer is close to, but not quite, one-half, since there is a very slight excess of aligned neutrons. For full credit, please carry your answer to as many decimal places as needed to see a deviation from 0.5.) !! € 1.8×108 !T#1!s#1 . € ± h 4π . Problem 45 light bulb m o b il e  b a r conducting rails B outward FigureforProblem2