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<html> <head> <meta content="en-us" http-equiv="Content-Language"> <meta content="text/html; charset=UTF-8" http-equiv="Content-Type"> <link type="text/css" rel="stylesheet" href="../../../../../css/ccna.css"> <script src="../../../../../js/framesetHelper.js" language="JavaScript"></script><script language="JavaScript"> window.scrollTo(0,0); function newPage(pageID) { alert("COMMING SOON!!\nThis feature is currently in development."); } function launchMoreInfo(oid) { dash = oid.indexOf('-'); sub1 = oid.substring(0,dash); sub2 = oid.substring(dash+1); // this is an URL base on the // system that generated the static // download of the curriculum. httpref = "http://nomar.sdf.cisco.com/servlet/org.cli.delivery.rendering.servlet.MIServlet/Static=true,LMSID=DTUI,Engine=dynamic,Theme=cnamstheme,Style=ccna,Language=en,Version=2,RootID=knet-v214aCV47051/CHAPID=null/RLOID=null/RIOID=null/"; newref = httpref + sub1 +"/"+ sub2 +"/moreinfoframeset.html"; //alert("new newref :\n" + newref); window.open(newref,'MoreInfo','toolbar=no,status=yes,menubar=no,location=no,scrollbars=yes,height=442,width=756,left=20,top=20,resizable=yes') } function launchContentResource(contentID) { top.currentSupport = 0; 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Simply put, most of the devices and processes involved in networking are electronic. While it is impossible to properly teach electronics in one chapter, we believe it essential to introduce some basic vocabulary. For some students, covering electronics will engage their prior experiences. For others, it may provide a point of focus for their future networking studies (many part-time jobs for younger students involve cable installation). Any discussion of copper-based media, for example, must involve some discussion of the media electrical properties. By performing some electronics labs, the students have an enjoyable, hands-on, effective way of learning such basic concepts as continuity and circuits. Anyone installing cable must have an awareness of conducting paths, short circuits, and open circuits. Also, much of Layer 1 and Layer 2 assumes a knowledge of electronics. Finally, the extensive use of frame, packet, and segment format diagrams (where the fields of these PDUs are discussed) is based, on a fundamental level, on the voltage versus time diagrams of an oscilloscope or logic analyzer displaying bit patterns.</p> <p>We view the Cisco Networking Academy Program (CNAP) as educating the future networking professionals of the world, not simply training them to pass a given test. We believe an educated networking professional understands some basic electronics [for example, most of the landmark texts in networking - for example, Computer Networks (by Tannenbaum) and Computer Networks (by Peterson and Davie) -- has substantial discussions of networking signals.</p> <p>There are two specific purposes to this target indicator. First, to relate what the student is about to learn (electrical signals) to prior knowledge from science classes. Secondly, to establish the foundation for understanding that electricity is comprised of electrons.</p> </span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table><p>All matter is composed of atoms. <i>"The Periodic Table of Elements"</i><img border="0" src="../../../../../CHAPID=knet-v214aCH47504/RLOID=knet-v214aRLO47542/RIOID=knet-v214aRIO121147/knet/v214adataimage1/1.gif" width="12" height="12">, lists all known types of atoms and their properties. The parts of the atom have several different names: </p><ul type="disc"><li> <i>nucleus</i> is the center part of the atom, formed by protons and neutrons </li><li> <i>protons</i> are particles that have a positive charge , and along with neutrons, form the nucleus </li><li> <i>neutrons</i> are particles that have no charge (neutral), and along with protons, form the nucleus </li><li> <i>electrons</i> are particles that have a negative charge, and orbit the nucleus</li></ul><p>To help you understand the electrical properties of elements/materials, locate "helium" on the periodic chart. It has an atomic number of 2, which means that it has 2 protons and 2 electrons. It has an atomic weight of 4. By subtracting the atomic number (2) from the atomic weight (4) you learn that helium also has 2 neutrons <img border="0" src="../../../../../CHAPID=knet-v214aCH47504/RLOID=knet-v214aRLO47542/RIOID=knet-v214aRIO121147/knet/v214adataimage2/2.gif" width="12" height="12">.</p><p>The Danish physicist Niels Bohr developed a simplified model to illustrate atoms. This illustration shows the model for a helium atom. Notice the scale of the parts. If the protons and neutrons of this atom were the size of a soccer ball, in the middle of a soccer field, the only thing smaller than the ball would be the electrons. They would be the size of cherries, and would be orbiting near the outer-most seats of the stadium. The only larger thing would be the space inside the atom, which would be the size of the soccer field.</p><table cellpadding="0" cellspacing="4" width="63%" border="0" xmlns:java="http://xml.apache.org/xslt/java"> <tr> <td valign="middle" width="8%"><img height="23" width="23" src="../../../../../images/ccna/common/icon2.gif"></td><td valign="middle" width="92%"><span class="cstitle">Web Links</span></td> </tr> <tr> <td valign="middle" width="8%"> </td><td valign="middle" width="92%"><span class="smtext"><a target="_blank" href="http://www.webelements.com/webelements/elements/text/He/key.html">Helium</a></span></td> </tr> </table></td> </tr> </table> </td> </tr></table> <p> </p> <table width="100%" cellspacing="0" cellpadding="2" border="0" valign="bottom"> <tr> <td></td> </tr> </table> </body></html>⌨️ 快捷键说明
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