25 - ELECTRIC CHARGES AND FORCES 25.1. Model: Use the...

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ELECTRIC CHARGES AND FORCES 25.1. Model: Use the charge model. Solve: (a) In the process of charging by rubbing, electrons are removed from one material and transferred to the other because they are relatively free to move. Protons, on the other hand, are tightly bound in nuclei. So, electrons have been removed from the glass rod to make it positively charged. (b) Because each electron has a charge of 1.60 x lo-'' C, the number of electrons removed is 25.2. Model: Use the charge model. Solve: (a) In the process of charging by rubbing, electrons are removed from one material and transferred into the other because they are relatively free to move. Protons, on the other hand, are tightly bound in the nuclei. So, electrons have been added to the plastic rod to make it negatively charged. (b) Because each electron has a charge of 1.60 x C, the number of electrons added is = 1.25 X 10" 20~10-~ c 1.60~ 10-l9 c 25.3. Model: Use the charge model. Solve: The mass of copper in a 2.0-mm-diameter copper ball is x m)' = 3.736 x kg = 0.03736 g 1 The number of moles in rhe ball is n=-= 0'03736 = 5.884 x lo4 mol A 63.5 glmol The number of copper atoms in the ball is N = nN, = (5.884 x lo4 mo1)(6.02 x loz3 mol-') = 3.542 x 10" We note that the number of electrons per atom is the atomic number, and both the atomic number (29) and the average atomic mass (63.5 g) are taken from the periodic table in the textbook. The number of electrons in the copper ball is thus 29 x 3.542 x IOz0 = 1.027 X 10". The number of electrons removed from the copper ball is So, the fraction of electrons removed from the copper ball is Assess: This is indeed a very small fraction of the available number of electrons in the copper ball. 25.4. Model: Use the charge model. Solve: oxygen. Because one proton has a charge of +1.60 x Each oxygen molecule has 16 protons (8 per atom), and there are 6.02 x lo2' oxygen molecules in 1 .O mole of C, the amount of positive charge in 1.0 mole of oxygen is 6.022 x x 16 x 1.6 x C = 1.54~ lo6 C
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25-2 Chapter 25 25.5. Model: Visualize: Use the charge model and the model of a conductor as a material through which electrons move. Glass Very fast * Charge transfer The charge carriers in a metal electroscope are the negative electrons. As the positive rod is brought near, electrons are attracted toward it and move to the top of the electroscope. The electroscope leaves now have a net positive charge, due to the missing electrons, and thus repel each other. At this point, the electroscope as a whole is still neutral (no net charge) but has been polarized. On contact, some of the electrons move to the positive rod to neutralize some (but not necessarily all) of the rod’s positive charge. After contact, the electroscope does have a net positive charge. When the rod is removed, the net positive charge on the electroscope quickly spreads to cover the entire electroscope. The net positive charge on the leaves causes them to continue to repel.
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This note was uploaded on 04/07/2008 for the course PHSX 211/212 taught by Professor Medvedev during the Spring '08 term at Kansas.

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25 - ELECTRIC CHARGES AND FORCES 25.1. Model: Use the...

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