mid1_practice_from_spring2010

# mid1_practice_from_spring2010 - UIC Physics 142 Spring 2010...

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UIC Physics 142 Spring 2010 Midterm Exam I Page 1 of 7 Name: __________________________ Physics 142 Midterm 1 Practice Exam PROBLEM POINTS SCORE 1 20 2 23 3 20 4 20 5 17 Total 100

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UIC Physics 142 Spring 2010 Midterm Exam I Page 2 of 7 Name: __________________________ 1. (20 points.) In the figure shown, two point charges, q 1 and q 2 , have the same size, . These two charges, along with an as-yet unknown charge q 3 , are placed so as to form an equilateral triangle (shown with solid lines) with sides of length d = 4 mm. The point P is at the exact center of the triangle, so that it is an equal dis- tance, r , from each of the three charges. a) Find the distance r from each of the charges to point P . (3 pts.) b) Assume that q 1 = q 2 . i) Find by direct calculation (that is, don’t use symmetry or other arguments) the value of q 3 , if any, that causes the net electric field to be zero, E = 0, at point P. (6 pts.) c) Assume that - q 1 = q 2 . i) Find by direct calculation (that is, don’t use symmetry or other arguments) the value of q 3 , if any, that causes the net electric field to be zero, E = 0, at point P. (5 pts.) ii) If q 1 = q 3 , find the net electric field vector, , at point P expressed in components. (6 pts.) q 1 = q 2 = + 5.0 10 9 C E 20 d q P
UIC Physics 142 Spring 2010 Midterm Exam I Page 3 of 7 Name: __________________________ 2. (23 pts) An insulating sphere of radius 0.5R, with uniform charge density with net charge -q is suspended inside a conducting spherical shell with inner and outer radii of R and 1.5R.

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mid1_practice_from_spring2010 - UIC Physics 142 Spring 2010...

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