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Unformatted text preview: brown (twb493) – Ch15-h1 – chiu – (56565) 1 This print-out should have 20 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A typical atomic polarizability is α = 1 × 10- 40 C · m N / C . If the q in p = qs is equal to the proton charge e , what charge separation s could you produce in a typical atom by applying a large field of 4 . 5 × 10 6 N / C? Correct answer: 2 . 8125 × 10- 15 m. Explanation: Recall that the magnitude of the dipole moment vector vectorp is equal to the polarizability α multiplied by the magnitude of the electric field vector vector E : | vectorp | = α vextendsingle vextendsingle vextendsingle vector E vextendsingle vextendsingle vextendsingle ⇒ p = αE. Since we also know that p = qs , we can use substitution to solve for the separation: p = αE s = αE q s = parenleftBig 1 × 10- 40 C · m N / C parenrightBig (4 . 5 × 10 6 N / C) 1 . 6 × 10- 19 C = 2 . 8125 × 10- 15 m . 002 10.0 points Which of the following statements are true. List all that apply separated by commas. If none of the statements is true, type “none”. A. A neutral atom is composed of both pos- itively and negatively charged particles. B. The positively charged particles in the nucleus are positrons. C. The electrons are attracted to the posi- tively charged nucleus. D. Positively charged protons are located in the tiny, massive nucleus. E. The radius of the electron cloud is twice as large as the radius of the nucleus. F. The negatively charged electrons are spread out in a “cloud” around the nu- cleus. Correct answer: A, C, D, F. Explanation: The first statement is true, because in order for an atom to be neutral, it must have equal amounts of positive and negative charge. The second statement is false. The positron is the antiparticle of the electron, which is not ordinarily observed outside of careful experi- ments. The positively charged particle in the nucleus is the proton. Statement C is true. Opposite charges at- tract, while like charges repel. Statement D is also true. The nucleus contains all the positive charge of the atom, and the electron cloud contains the negative charge. Statement E is false. The order of mag- nitude of the radius of the electron cloud is 10- 10 m, while the order of magnitude of that of the nucleus is 10- 15 m. The electron cloud is far larger than the nucleus. Statement F is true. In the semiclassi- cal description, an electron is moving along an orbit, while in the quantum mechanical description, the motion of an electron is de- scribed by a probability wave function. Thus the electron’s charge is spread out in a prob- ability distribution about the orbit called an “electron cloud.” 003 10.0 points There is a region where an electric field points to the right, due to charged particles some- where. A neutral carbon atom is placed inside this region. Draw a diagram of the situation, and use it to determine whether the following...
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This note was uploaded on 12/01/2011 for the course PHY 303L taught by Professor Turner during the Fall '08 term at University of Texas.
- Fall '08