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Unformatted text preview: Solution for Homework 2 Simple Electric Devices and Processes Solution to Homework Problem 2.1(Determine the Sign of Charge Induced on Con- ducting Spheres in Contact) Problem: If you bring a negatively charged insulating rod near two neutral metallic spheres that are in contact and then separate the spheres without grounding either, the sphere farthest from the insulator will have: Select One of the Following: (a) no net charge (b) a net positive charge (c-Answer) a net negative charge (d) either a net positive or a net negative charge Solution The negatively charged rod causes the charge in the two conducting spheres to separate. The negative charge is repelled toward the second sphere and is isolated from the positive charge in the first sphere when the contact between the two is broken, leaving it with a net negative charge. Total Points for Problem: 3 Points Solution to Homework Problem 2.2(Electroscope with a Plastic Bolt) Problem: While constructing a leaf electroscope, a student finds the paperclip that connects the bolts to the leaves difficult to work with. To make construction easier, the student uses a plastic tie wrap instead to connect the bolt to the foil leaves. How does this substitution affect the operation of the electroscope? Select One of the Following: (a) The operation is unchanged. (b-Answer) The electroscope will cease to function. (c) The leaves of the electroscope will attract, rather than repel. (d) The electroscope will only detect charge of one sign. Solution Plastic is an insulator, so the electroscope will do nothing. Total Points for Problem: 3 Points Solution to Homework Problem 2.3(Interaction of Charged and Uncharged Objects if Electric Force is Constant with Distance) Problem: A neutral object is placed in a region of space where the electric force does not depend on distance from the charge. What is the direction of the force exerted on the neutral object? Select One of the Following: 1 (a-Answer) There is no force. (b) Toward the object exerting the force. (c) Away from the object exerting the force. Solution In a universe where the electric force between two charged particles is independent of the distance between the particles, a charged object cannot attract an object with no net charge, even if the neutral object is polarized. The charged object will attract those charges opposite its own net charge in the neutral object with as much force as it repels those charges like its own. Therefore, there will be zero net electric force between the two objects. Total Points for Problem: 3 Points Solution to Homework Problem 2.4(Experimental Support for: Objects Attract, then Repel after Making Contact) Problem: A neutral insulating ball is suspended from a string. As a charged insulating rod is brought near the ball, the ball swings toward the rod, makes contact, then swings away. Why?...
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