TAILIEUCHUNG - CCNA 1 and 2 Companion Guide, Revised (Cisco Networking Academy Program) part 16

Cisco Networking Academy Program CCNA 1 and 2 Companion Guide, Revised part 16 is the Cisco approved textbook to use alongside version of the Cisco Networking Academy Program CCNA 1 and CCNA 2 web-based courses. The topics covered provide you with the necessary knowledge to begin your preparation for the CCNA certification exam (640-801, or 640-821 and 640-811) and to enter the field of network administration. | Page 119 Tuesday May 20 2003 2 53 PM Measuring Electricity 119 Voltage Because electrons and protons have opposite charges they are attracted to each other with a force similar to the attractive force of the north and south poles of two magnets. When the charges are separated this separation creates an attractive force or pressure field between the charges. This force is voltage. The force that is created pulls toward the opposite charge and pushes away from the like charge. This process occurs in a battery where chemical action causes electrons to be freed from the battery s negative terminal and to travel to the opposite or positive terminal through an external circuit not through the battery itself. The separation of charges results in voltage. Voltage can also be created by friction static electricity by magnetism electric generator or by solar energy. Voltage is represented by the letter V. The unit of measurement for voltage is the volt and it is also represented with the letter V for example 12 V 12 volts . Two kinds of voltage exist Direct-current DC voltage A battery is an example of a DC voltage source. The movement of electrons in a DC circuit is always in the same direction from negative to positive. Alternating-current AC voltage In an AC circuit the positive and negative terminals of the AC voltage source regularly change to negative and positive and back again as shown in Figure 3-3. This change makes the direction of electron movement change or alternate with respect to time. Figure 3-3 Alternating Current Lab Activity Safe Handling and Use of a Multimeter In this lab you learn how to use or handle a multimeter correctly. Lab Activity Voltage Measurements In this lab you demonstrate the ability to measure voltage with the multimeter. Page 120 Tuesday May 20 2003 2 53 PM 120 Chapter 3 Networking Media Current Electrical current is the flow of charges that is created when electrons move. When voltage electrical pressure is applied

• Chứng chỉ quốc tế
• Luyện thi CCNA
• kỹ năng xử lý sự cố
• chương trình học viện mạng Cisco
• làm quen với quản trị mạng
• công nghệ Ethernet
• TCP IP
• phương tiện truyền thông mạng IP
• địa chỉ IP
• định tuyến giao thức
• chứng chỉ CCNA
• trắc nghiệm CCNA
• bài tập CCNA
• tài liệu CCNA
• Giáo trình CCNA
• Phần mềm CISCO
• Lập trình mạng
• CCNA1 Practice Final
• quản trị mạng
• luyện thi chứng chỉ quốc tế
• chương trình Cisco