Final_exam_Sample_test_with_solutions_old

# Final_exam_Sample_test_with_solutions_old - Department of...

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Department of Physics, Lehigh University Physics 21 – Introductory Physics II Spring 2010 Final Exam May 9, 2010Q ver 4 Closed Notes 8:00 AM-11:00 AM Student’s Name__Solutions______________ Recitation Section Number______________ Recitation Leader’s Name_____________________________ First, check to be sure that you have a 15-page examination, not including the cover sheet, equation sheet or the 2 pages of scrap paper. The test is a multiple-choice examination. Read all choices and choose the best response. Please answer each question by writing the letter corresponding to your choice in the answer area. Answers marked outside the answer areas will not be scored.

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1. In crystals of the salt cesium chloride, cesium ions form the eight corners of a cube and a chlorine ion is at the cube's center. The edge length of the cube is 0.40 nm. The ions are each deficient by one electron (and thus each has a charge of ), and the ion has one excess electron (and thus has a charge of ). A) What is the magnitude of the net force on the ion? (a) (b) (c) (d) Answer: ____b_____ B) If one of the ions is missing, what is the magnitude of the net force? (a) (b) (c) (d) Answer: ____a_____ C) What is the direction of the force on the ion when the ion is removed? (a) Zero Net Force (b) Away from the missing ion (c) Toward the missing ion (d) None of the above Answer: ____b_____ D) Now a total of four of the ions are removed from one face of the cube, what is the magnitude of the net electric field at the center of the opposite cube face? (a) (b) 0 (c) (d) Answer: ____d_____ E) What would be the net electric flux through the face of the cube with the four missing ions? (a) (b) (c) (d) Answer: ____d_____
2. A parallel-plate capacitor has square plates with a width of 8.0 cm filled with air has capacitance C=0.56 nF. A) What is the gap size between the plates? (a) 2 mm (b) 0.1 mm (c) 0.2 mm (d) 0.02 mm Answer:____b_____ B) What is the charge on the plates if a potential difference of 125 V is applied across them? (a) 5.0x10 -10 C (b) 0.70 x 10 -7 C (c) 2.0x10 10 C (d) 0.35 x10 -6 C Answer:____b_____ C) The energy stored in the capacitor is (a) 0.42 μJ (b) 4.4 μJ (c) 84 μJ (d) 0.072 μJ Answer:____b_____ D) With the left half of the gap is filled with material of dielectric constant κ 1 = 5.0 and the right half is filled with material of dielectric constant κ 2 = 10, as shown in the figure to the right. What is the capacitance of the capacitor? (a) 9.0 nF (b) 28 nF (c) 4.2 nF (d) 3.7 nF Answer:____c_____ E) Now, if the bottom half of the gap is filled with material of dielectric constant κ 1 = 5 and the top half is filled with material of dielectric constant κ 2 = 10, as shown in the figure to the right. What is the capacitance of the capacitor? (a) 9.0 nF (b) 28 nF (c) 4.2 nF (d) 3.7 nF Answer:____d_____

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3. Four concentric spherical non-conducting surfaces (as shown) have equal amounts of charge distributed uniformly over them, with alternating signs: A of radius 1.0 cm has a total charge +150 μC B of radius 10 cm has a total charge -150 μC C of radius 20 cm has a total charge +150 μC D of radius 30 cm has a total charge -150 μC These are surface charges. There is no charge between the surfaces.
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Final_exam_Sample_test_with_solutions_old - Department of...

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