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The Only Authorized Textbook for the Cisco Networking Academy Program
Cisco Networking Academy Program: First-Year Companion Guide, Second Edition is the Cisco-approved textbook for the first and second semesters of the Cisco Networking Academy Program.
This book supports and reinforces the Web-based curriculum for the Cisco Networking Academy Program, while reinforcing concepts pertaining to CCNA certification. The first-year guide provides an in-depth discussion of the OSI reference model layers and path determination, in addition to the configuration details for IP routing and addressing, subnetting topics, and basic router configuration and operation.
The instructional materials for the First-Year Companion Guide follow the instructional style and format that Cisco Systems has created for the Cisco Networking Academy Program and is the only print companion that Cisco Systems reviewed and endorses for the Cisco Networking Academy Program
After reading this chapter, you will be able to
In this chapter, you learn about the basic theory of electricity, which provides a foundation for understanding networking at the physical layer of the OSI model. You also learn how data is transmitted through physical media, such as cables and connectors. Last, you learn about the different factors that affect data trans-mission, such as alternating current (AC) power line noise.
The names of the parts of the atom are
Figure 4-1 The Periodic Table of Elements....
...The Danish physicist, Niels Bohr, developed a simplified model to illustrate atoms. Figure 4-2 shows the model for a helium atom. Notice the scale of the parts. If the protons and the 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 outermost seats of the stadium. The only thing larger than the soccer ball would be the space inside the atom, which would be the size of the soccer field.
Figure 4-2 The helium atom has two protons, two electrons, and two neutrons....
Examine Bohr’s model of the helium atom. If Coulomb’s Law is true, and if Bohr’s model describes helium atoms as stable, other laws of nature must be at work. How can they both be true?
Coulomb’s Law—Opposite charges attract.
Bohr’s model—Protons are positive charges, and electrons are negative charges.
Question 1: Why don’t the electrons fly in toward the protons?
1. Coulomb’s Law—Like charges repel.
2. Bohr’s model—Protons are positive charges. There is more than one proton in the nucleus.
Question 2: Why don’t the protons fly away from each other?
The answer to these questions is that other laws of nature must be consid-ered. Following are the answers to each of the above questions.
Answer 1: The electrons stay in orbit, even though they are attracted by the protons. They have just enough velocity to keep orbiting, just like the moon around the Earth, and to not let themselves be pulled into the nucleus.
Answer 2: The protons do not fly apart from each other because of a nuclear force that is associated with neutrons. The nuclear force is an incredibly strong force that acts as a kind of glue to hold the protons together.
The protons and neutrons are bound together by a powerful force; however, the force that binds electrons to their orbit around the nucleus is weaker. Figure 4-3 illustrates these forces. Electrons in certain atoms can be pulled free from the atom and made to flow. This is electricity—a free flow of electrons.
Posted April 22, 2003
This book is part of the curriculum for the Cisco Networking Academy Program. However, I would also look into buying several more books from the CCNA to CCNP level to cover any blank spots on Cisco networking...Was this review helpful? Yes NoThank you for your feedback. Report this reviewThank you, this review has been flagged.