HW9 - MasteringPhysics 5/10/09 3:33 PM Assignment Display...

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5/10/09 3:33 PM MasteringPhysics Page 1 of 8 http://session.masteringphysics.com/myct Assignment Display Mode: View Printable Answers phy260S09 HW9 Due at 11:00pm on Thursday, April 16, 2009 View Grading Details Charged Aluminum Spheres Description: Find the number of electrons in an aluminum sphere. Calculate the number of electrons that must be removed from one sphere and added to another to create a given attractive force, and find the fraction of electrons per sphere this number represents. Two small aluminum spheres, each of mass 0.0250 kilograms, are separated by 80.0 centimeters. Part A How many electrons does each sphere contain? (The atomic mass of aluminum is 26.982 grams per mole, and its atomic number is 13.) Hint A.1 The definition of mole and atomic number In one mole ( ) of any material, there are approximately atoms present. The number of atoms per mole is called Avogadro's number . The atomic number of an element is the number of protons (and therefore also the number of electrons) in an atom of that element. Hint A.2 How many electrons per mole of aluminum? How many electrons are there in a mole of aluminum? Express your answer numerically. ANSWER: Hint A.3 How many electrons per kilogram of aluminum? How many electrons are in a kilogram of aluminum? Express your answer numerically. ANSWER: Express your answer numerically. ANSWER: Part B How many electrons would have to be removed from one sphere and added to the other to cause an attractive force between the spheres of magnitude (roughly one ton)? Assume that the spheres may be treated as point charges. Hint B.1 How to approach the problem Use Coulomb's law to find the charge needed to produce the given force. Then use the charge of an electron to determine the number of electrons necessary to produce the calculated charge. Hint B.2 Find the relationship between the charges of the spheres Assume that after some electrons have been removed from it, the first sphere ends up with a net charge of . What would be the charge on the other sphere, , after these extra electrons are added to it? Express your answer in terms of and any necessary constants. ANSWER: = Express your answer numerically. [ Print ]
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5/10/09 3:33 PM MasteringPhysics Page 2 of 8 http://session.masteringphysics.com/myct ANSWER: Part C What fraction of all the electrons in one of the spheres does this represent? Express your answer numerically. ANSWER: Problem 26.44 Description: (a) What is the force F_vec on the 1.0nC charge in the middle of the figure due to the four other charges? Give your answer in component form. Part A What is the force on the 1.0 charge in the middle of the figure due to the four other charges? Give your answer in component form. Assume that -axis is directed horizontally to the right, and -axis is directed vertically upward.
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HW9 - MasteringPhysics 5/10/09 3:33 PM Assignment Display...

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