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Unformatted text preview: pan (zp695) – Ch15-h2 – chiu – (56565) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 (part 1 of 2) 10.0 points A positively charged sphere is placed near a neutral block of nickel, as shown in the following figure. + + + + + + + + Neutral nickel block Charged sphere Which of the diagrams below best repre- sents the equilibrium distribution of charge on the neutral nickel block? C A D B-------- + + + + + + + + +- +- +- +- Correct answer: B. Explanation: The mobile electrons are attracted by the positively charged sphere at the right. Here E block due to the charges on the block is to the right, which is to be canceled by the field of the positive sphere, E sphere , pointing to the left. Among the four blocks illustrated, B has the best chance for the cancellation of net field inside of the block, leading to E block + E sphere = 0 , i.e. , in equilibrium condition. 002 (part 2 of 2) 10.0 points At location P inside the nickel block the elec- tric field due to the charged sphere is E =- 625 , , N / C . At equilibrium, which of the following state- ments must be true? A. It is not possible to determine the electric field at location P due only to charges surface of the nickel block. B. The electric field at location P due only to charges on the surface of the nickel block is E = , , N / C C. Because the net electric field at location P is E = , , N / C , the field at P due only to charges on the surface of the polarized nickel block must be E = 625 , , N / C . Correct answer: C. Explanation: The first statement is incorrect since once the charges are given, the field contributed by that charge can always be uniquely de- termined. The second statement is incorrect also. We know that E block + E sphere = 0 . However, here, E block is not zero. By in- spection it should be pointing to the right. The third statement is the correct one. From above it is given that E sphere =- 625 , , N / C . With E block + E sphere = 0 , we have E block = 625 , , N / C . 003 10.0 points You run your finger along the slick side of pan (zp695) – Ch15-h2 – chiu – (56565) 2 a positively charged tape, and then observe that the tape is no longer attracted to your hand. Which of the following are not plausible explanations for this observation? List all that apply, separated by commas. If none apply, type “none”. A. Sodium ions (Na + ) from the salt water on your skin move onto the tape, leaving the tape with a zero (or very small) net charge. B. Electrons from the mobile electron sea in your hand move onto the tape, leaving the tape with a zero (or very small) net charge....
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This note was uploaded on 02/21/2012 for the course PHY 303K taught by Professor Turner during the Spring '08 term at University of Texas.
- Spring '08