The Physics Factbook™
Edited by Glenn Elert -- Written by his students
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|Bibliographic Entry||Result |
|Brown, Theodore L. LeMay, Eugene, Bursten, Jr., Bruce. Chemistry: the Central Science. New Jersey: Prentice-Hall, 1997.||"A 12 V lead-storage battery consists of six cells, each producing 2 V."||12 V|
|Andrea, J. David, Flynn, Michael S. "Automobile." World Book. Chicago: World Book, 1998: Vol. 1, 954.||"A 12 volt battery"stores energy for the starter, which begins the operation of the electrical system by cranking the engine to life."||12 V|
|"Hints & Kinks." QST. December 1997: 69.||"The most convenient power source is usually the 12 V battery in the vehicle that gets us there, and modern solid-state devices work fine at 12 V, or less."||12 V|
|Giancoli, C. Douglass. Physics: Principles with Applications. New Jersey: Prentice-Hall, 1980.||"Thus the voltage between the ends of the 2 flashlight batteries in Figure 15-5 a is 3 V while the six 2 V cells of the storage battery in part b give 12 V."||12 V|
|Cutnell, John D., Johnson, Kenneth W. Physics. New York: Wiley, 1995.||"The voltage rises by 12.0 V due to the battery's emf. However, the voltage drops by 0.10 V because of the potential difference across the internal resistance. Therefore, the terminal voltage is 12.0 V–0.10 V = 11.9 V"||11.9 V |
(at 10 A)
|"When the current through the battery is 100.0 A, the amount of voltage needed to make the current go through the internal resistance is V= (100 A)(0.01 ohm) = 1.0 V. The terminal voltage of the battery now decreases to 12.0 V–1.0 V = 11.0 V."||11 V |
(at 100 A)
One of the most common and useful batteries is the lead-storagebattery used in automobiles. The cell of the lead storage batteryconsists of alternate plates of lead (cathode) and lead coatedwith lead dioxide (anode) immersed in an electrolyte of sulfuricacid solution. A 12 V lead-storage battery consists of sixcells, each producing approximately 2 V. The actual standardcell potential is obtained from the standard reduction potentials.
E = E (cathode)–E (anode) = (+1.685 V)–(-0.356 V) = + 2.041 V
6 cells x 2.041 V/cell = 12.246 V
Because of the positive and negative charges on the batteryterminals, an electric potential difference exists between them.This potential difference is called the electromotive force (emf)of the battery. This is a poor term because emf is not a forcebut an energy per unit charge quantity, like potential. The SIunit of emf is the volt (V = J/C = joule/coulomb).
A car battery is an example of a source of emf. An ideal sourceof emf maintains a constant potential difference between its terminals,independent of the current, I, through it or the resistance,R, across it. The formula for an ideal source of emf isV= IR, which is known as Ohm's Law. The potentialdifference across a real source in a circuit, however, is notequal to the ideal emf. The reason is that charge moving throughthe material of any real source encounters an internal resistancer and experiences a drop in potential difference equalto Ir. Thus the equation for a source with internal resistanceis V = emf - Ir and this potential is called the terminal voltage.Therefore the voltage in a car battery is always less than 12 Vwhile it is producing a current.
Thi Meagan Le -- 2001
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