Final_2006Spring_Solutions - MIT Department Of Physics p. 1...

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MIT Department Of Physics p. 1 of 15 Problem 1: Eight Short Questions. Circle your choice for the correct answer Each problem is worth 5 points for the correct answer, 2 points for a partially correct answer (at our discretion). If you don’t know the answer you can earn 1 point for admitting that by leaving it unanswered and writing “I don’t know” (make this clear!). Question A (5 points out of 40 points): In lab 1 you fixed the potential difference between two plates and measured equipotential lines from which you determined electric field lines and approximate charge distributions. You are given a layout with a conducting plate and conducting circle, as pictured at left, with the circle held at +5 V relative to the plate. Identify the most accurate representation of the equipotential lines and the electric field lines: Equipotential Lines: #____4 _____ Electric Field Lines: #_____5 ______ Field lines must be perpendicular to surfaces. Equipotentials must be closest where field is strongest (between conductors) Question B (5 points out of 40 points): In the second lab you worked with a Faraday pail, two nested conducting cylinders as pictured at left (in the lab the shaded regions were thin). You held the outer cylinder at ground (i.e. at the same potential as infinity) and measured the potential of the inner cylinder relative to the outer cylinder. For one of the measurements you started from a condition where both cylinders were uncharged, introduced a positive charge producer into the central region, briefly connected the inner at outer cylinders with a conductor (your finger) and, after removing the connection, removed the positive charge producer. The positive charge producer never touched either of the cylinders during this measurement. Identify (circle) the sign of the charge (positive, negative or zero) on ea I1 I2 O1 O2 ch surface after doing this: I1: >0 <0 O1: >0 =0 I2: =0 <0 O2: >0 <0 When touching the two together negative charges flow to the inner conductor to shield the positive charge. In the end they move to O1 and positive charges shield them at I2. Nothing is at O2 because it is grounded, or at I1 because it is an interior surface.
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MIT Department Of Physics p. 2 of 15 Question C (5 points out of 40 points): In the third lab you studied the effects of magnetic fields. A current-carrying coil is placed in a uniform magnetic field pointing to the right. The current flows as shown, out of the page in the upper left and in on the lower right. B I I What are the direction of the force and torque on the coil (circle one direction for each)? Force (dipole will tend to move…): Mostly left Mostly Right Torque (dipole will tend to rotate…): Counterclockwise None No force in a uniform field. The dipole moment is up and to right (from right hand rule) so torque to align makes it rotate clockwise.
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This note was uploaded on 04/07/2008 for the course 8 8.02 taught by Professor Hudson during the Fall '07 term at MIT.

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Final_2006Spring_Solutions - MIT Department Of Physics p. 1...

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