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Unformatted text preview: soto (rrs946) Homework 5 Hoffmann (56605) 1 This print-out should have 10 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points A 43 m length of coaxial cable has a solid cylindrical wire inner conductor with a di- ameter of 3 . 558 mm and carries a charge of 12 . 34 C. The surrounding conductor is a cylindrical shell and has an inner diameter of 11 . 188 mm and a charge of- 12 . 34 C. Assume the region between the conductors is air. The Coulomb constant is 8 . 98755 10 9 N m 2 / C 2 . What is the capacitance of this cable? Correct answer: 2 . 08808 nF. Explanation: Let : k e = 8 . 98755 10 9 N m 2 / C 2 , Q = 12 . 34 C , = 43 m , a = 3 . 558 mm , and b = 11 . 188 mm . The charge per unit length is Q . V =- integraldisplay b a vector E dvectors =- 2 k e integraldisplay b a dr r =- 2 k e Q ln parenleftbigg b a parenrightbigg . The capacitance of a cylindrical capacitor is given by C Q V = 2 k e 1 ln parenleftbigg b a parenrightbigg = 43 m 2 (8 . 98755 10 9 N m 2 / C 2 ) 1 ln parenleftbigg 11 . 188 mm 3 . 558 mm parenrightbigg parenleftbigg 1 10 9 nF 1 F parenrightbigg = 2 . 08808 nF 002 10.0 points A parallel-plate capacitor is charged by con- necting it to a battery. If the battery is disconnected and then the separation between the plates is increased, what will happen to the charge on the capac- itor and the electric potential across it? 1. The charge increases and the electric po- tential decreases. 2. The charge increases and the electric po- tential remains fixed. 3. The charge and the electric potential de- crease. 4. The charge and the electric potential in- crease. 5. The charge remains fixed and the electric potential increases. correct 6. The charge decreases and the electric po- tential increases. 7. The charge remains fixed and the electric potential decreases....
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This note was uploaded on 11/10/2011 for the course PHYSICS 303L taught by Professor Hoffman during the Fall '11 term at University of Texas at Austin.
- Fall '11