2008BAP 1 Solutions

Image is on the same side of the mirror as the object

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Unformatted text preview: e. Image could be projected on a screen. Object is placed beyond the focal point of a converging mirror. 1 point 1 point (c) 2 points For a correct mirror equation and at least one step toward a correct solution 1 1 1 1 1 1 + = , leading to = , for example si so f si f so Substituting into the second equation above 1 1 1 8-6 1 2 1 = = = si 6.0 cm 8.0 cm 48 cm 48 cm For a correct calculation with correct units, consistent with substitutions made si = 24 cm 1 point 1 point 2008 The College Board. All rights reserved. Visit the College Board on the Web: www.collegeboard.com. AP PHYSICS B 2008 SCORING GUIDELINES Question 6 (continued) Distribution of points (d) 3 points For correctly indicating that the image is smaller than the object For a correct justification Numerical justification: 1 1 1 = si f so 1 point 2 points 1 1 1 8+6 1 14 1 = = = si -6.0 cm 8.0 cm 48 cm 48 cm si = -3.4 cm si -3.4 cm == 0.43 so 8.0 cm Qualitative justifications: Diverging mirrors always form an image that is smaller than the object. si < so and so hi < ho . The student must prove the inequality with calculations or a diagram. Ray diagram justification: M =- The ray diagram must contain at least two correct rays that show reflection and correctly show the image upright and smaller than the object, between the focal point and the mirror. The student must specifically indicate that his/her ray diagram is the justification to earn any points for it. An incomplete but not incorrect justification earns 1 point. 2008 The College Board. All rights reserved. Visit the College Board on the Web: www.collegeboard.com. AP PHYSICS B 2008 SCORING GUIDELINES Question 7 10 points total Distribution of points (a) 2 points For correct substitutions into the relationship between the de Broglie wavelength and the momentum h p= l 6.63 10 -34 Jis 0.038 10 -9 m For a correct answer kgim p = 1.74 10 -23 s p= 1 point 1 point (b) 2 points Calculating the speed of an electron p 1.74 10 -23 kgim s u = = = 1.91 107 m s -31 m 9.11 10 kg For correct substitutions into a correct expression for kinetic energy 1 K = mu 2 2 2 1 K = 9.11 10 -31 kg 1.91 10 7 m s 2 For a correct answer K = 1.66 10 -16 J 1 point ( )( ) 1 point (c) 3 points For any indication of conservation of energy K = qV For correct substitutions into a correct expression 1.66 10 -16 J K V = = q 1.60 10 -19 C 1 point 1 point ( ( ) ) For a correct answer V = 1.04 103 V 1 point 2008 The College Board. All rights reserved. Visit the College Board on the Web: www.collegeboard.com. AP PHYSICS B 2008 SCORING GUIDELINES Question 7 (continued) Distribution of points (d) 3 points For any indication that this process is the photoelectric effect K max = hf - f For recognizing that K max = 0 1 point 1 point f 4.5 eV = h 4.14 10 -15 eVis For a correct answer with units f = 1 point f = 1.09 10 15 Hz 2008 The College Board. All rights reserved. Visit the College Board on the Web: www.collegeboard.com....
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