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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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But in our discussions of where to put wiring closets, where to run cable, which backbone cabling to use, and others, electrical issues play an important role.</p> </span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table><p>Electricity is a fact of modern life. It is used to perform a variety of tasks. It is brought into homes, schools, and offices by power lines that carry it in the form of alternating current (AC). Another type of current called direct current (DC), is the kind found in a flashlight, car battery, and in the motherboard of a computer.</p><p>It is important to understand the difference between these two types of current flow. DC has constant voltage. To see how this works, refer to Figure <img border="0" src="../../../../../CHAPID=knet-v214aCH47508/RLOID=knet-v214aRLO47689/RIOID=knet-v214aRIO121739/knet/v214adataimage1/1.gif" width="12" height="12">. As illustrated, the battery supplies current during a given period of time at a constant level of current flow.</p><p>AC rises and falls in current values as power companies manufacture it. This rise and fall can be explained by the series of graphics as described below.</p><p>Figure <img border="0" src="../../../../../CHAPID=knet-v214aCH47508/RLOID=knet-v214aRLO47689/RIOID=knet-v214aRIO121739/knet/v214adataimage2/2.gif" width="12" height="12"> depicts the rise to the peak of current flow as the south pole moves across the core of the coil.</p><p>Figure <img border="0" src="../../../../../CHAPID=knet-v214aCH47508/RLOID=knet-v214aRLO47689/RIOID=knet-v214aRIO121739/knet/v214adataimage3/3.gif" width="12" height="12"> depicts the fall to 0 current flow as the two poles straddle the core and balance current flow to 0 value.</p><p>Figure <img border="0" src="../../../../../CHAPID=knet-v214aCH47508/RLOID=knet-v214aRLO47689/RIOID=knet-v214aRIO121739/knet/v214adataimage4/4.gif" width="12" height="12"> depicts the rise to opposite polarity peak (a negative value) as the north pole moves across the core of the coil.</p><p>Figure <img border="0" src="../../../../../CHAPID=knet-v214aCH47508/RLOID=knet-v214aRLO47689/RIOID=knet-v214aRIO121739/knet/v214adataimage5/5.gif" width="12" height="12"> depicts the fall to 0 current flow as the magnet exits the coil area. AC power as manufactured for delivery to homes uses this concept.</p></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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