The circuit e text main menu textbook table of

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ly made from metallic alloys and carbon compounds. The circuit | e-Text Main Menu | Textbook Table of Contents | Problem Solving Workbook Contents CHAPTER 2 Basic Laws 29 symbol for the resistor is shown in Fig. 2.1(b), where R stands for the resistance of the resistor. The resistor is the simplest passive element. Georg Simon Ohm (1787–1854), a German physicist, is credited with finding the relationship between current and voltage for a resistor. This relationship is known as Ohm’s law. Ohm’s law states that the voltage v across a resistor is directly proportional to the current i flowing through the resistor. That is, v∝i (2.2) Ohm defined the constant of proportionality for a resistor to be the resistance, R . (The resistance is a material property which can change if the internal or external conditions of the element are altered, e.g., if there are changes in the temperature.) Thus, Eq. (2.2) becomes v = iR (2.3) which is the mathematical form of Ohm’s law. R in Eq. (2.3) is measured in the unit of ohms, designated . Thus, The resistance R of an element denotes its ability to resist the flow of electric current; it is measured in ohms ( ). We may deduce from Eq. (2.3) that R= v i + v=0 R=0 so that 1 − = 1 V/A To apply Ohm’s law as stated in Eq. (2.3), we must pay careful attention to the current direction and voltage polarity. The direction of current i and the polarity of voltage v must conform with the passive sign convention, as shown in Fig. 2.1(b). This implies that current flows from a higher potential to a lower potential in order for v = iR . If current flows from a lower potential to a higher potential, v = −iR . Since the value of R can range from zero to infinity, it is important that we consider the two extreme possible values of R . An element with R = 0 is called a short circuit, as shown in Fig. 2.2(a). For a short circuit, v = iR = 0 v v | e-Text Main Menu | Textbook Table of Contents | (a) + v i=0 R=∞ − (2.5) showing that the voltage is zero but the current could be anything. In practice, a short ci...
View Full Document

This note was uploaded on 07/16/2012 for the course KA KA 2000 taught by Professor Bkav during the Spring '12 term at Cambridge.

Ask a homework question - tutors are online