Question

1. In class, we calculated the electrostatic force between sodium and chlorine ions in NaCl, which is an example of an ionic bond Another type of chemical bond is a covalent bond, where electrons are shared between atoms, like in a hydrogen molecule, H2. We can try to model this as a collection of three charges, with the two nuclei treated like two +e charges, and the two electrons treated as one -2e charge. (20 points) If the electrons are in the middle between the hydrogen nuclei, and the atoms are 7.4x10-11 m apart, what is the energy of the collection of charges? a. (5 points) The actual amount of energy in this covalent bond is 7.2x1019 J. Why is the actual value different from the value in part a? (Hint: What would happen if you connected the two hydrogen atoms with a spring?) b. 2. The charges in batteries are usually measured in in ampere-hours, which is a large unit of charge. A typical 9V battery is able to supply about 0.1 ampere-hours of charge, equal to 360 coulombs (5 points) If you attach a machine to a 9V battery, what is the total energy that the battery will be able to supply to the machine? a. b. (5 points) Suppose the machine is a motorized winch designed to lift a 500 gram weight. What is the total distance that the machine can lift the weight? 3. (15 points) You are designing a new capacitor to be mass produced, and must decide which dielectric should be used to make it. You want the capacitor to be small, with an area of 1 square centimeter, and a thickness of 2.5 um. You want your new capacitor to be able to work in a circuit with up to 1.5 V across the capacitor, and it must be able to store up to 10° J of energy. There are three dielectrics that are readily available that you can choose from, whose properties are shown in the table below. Which one should you choose to minimize the cost of production? MaterialCost per ton Dielectric constant Max. Electric Field (MV/m) Dielectric A $143.21 DielectricB $176.09 DielectricC $119.20 900 1040 1390 1.106 0.881 0.516

Answer 1

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Conservoh»η 아. Energy G GI 2.2 m 3 -12 2- ー10 3-1843 x to l o kim 3-1843