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Unformatted text preview: 7 10 -8 Wim ) 1 point 1 point For a correct answer with correct units L = 0.72 m Note: The last 2 points could be earned for showing understanding of R = rL A by using it with the appropriate values of r and A and some value of resistance. (b) 4 points The force on the magnet is upwards. Points are awarded for the justification as follows. For indicating that the right-hand rule should be used For correctly identifying the direction of the magnetic field between the poles of the magnet as being to the right For obtaining a downward force on the wire using the right-hand rule Example for the above 3 points: The direction of the force on the wire is given by the right-hand rule. The current is into the page and the magnetic field is to the right. By the right-hand rule, the force on the wire is then downwards. For using Newton's 3rd Law For example: The force on the wire is downwards, so the force on the magnet must be upwards. Note: A student who checks "downward" can receive 3 of 4 points if they correctly use the right-hand rule to show that the force on the wire is downward. Just checking the box "upward" without justification received no points. 2008 The College Board. All rights reserved. Visit the College Board on the Web: www.collegeboard.com. 1 point 1 point 1 point 1 point AP PHYSICS B 2008 SCORING GUIDELINES
Question 3 (continued)
Distribution of points (c) 3 points For simplifying the formula given in the equation table for the force on a currentcarrying wire (or stating that q = 90 ) F = ILB For correct substitutions (0.060 N ) F B= = IL ( 4.0 A )(0.020 m ) For a correct answer with correct units B = 0.75 T (d) 3 points 1 point 1 point 1 point For a straight-line relationship For a relationship that passes through the origin For a slope less than the original line but NOT zero (e) 1 point For a plausible source of error that would produce the plotted results For example: The horizontal width of the wire approaches the width of the magnet. Near the edges of the mag...
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This note was uploaded on 02/09/2011 for the course PHYS 10 taught by Professor Davidnewton during the Spring '11 term at DeAnza College.
- Spring '11