The atom is comprised of:

1. The atom is comprised of: • Electrons – Particles with a negative charge that orbit the nucleus • Nucleus – The center part of the atom, composed of protons and neutrons • Protons – Particles with a positive charge • Neutrons – Particles with no charge (neutral)

3. Electrons in certain atoms, such as metals, can be pulled free from the atom and made to flow • Electricity is a free flow of electrons

4. Loosened electrons that stay in one place, without moving, and with a negative charge, are called static electricity • ESD, though usually harmless to people, can create serious problems for sensitive electronic equipment.

5. Atoms, or groups of atoms called molecules, can be referred to as materials. Materials are classified as belonging to one of three groups depending on how easily electricity, or free electrons, flows through them.

6. The basis for all electronic devices is the knowledge of how insulators, conductors and semiconductors control the flow of electrons and work together in various combinations.

7. Voltage • Voltage is sometimes referred to as electromotive force (EMF) • Voltage can also be created in three other ways. The first is by friction, or static electricity. The second way is by magnetism, or electric generator. The last way that voltage can be created is by light, or solar cell.

8. The unit of measurement for voltage is volt (V). • Volt is defined as the amount of work, per unit charge, needed to separate the charges.

9. Resistance and impedance • The materials through which current flows offer varying amounts of opposition, or resistance to the movement of the electrons.

10. Conductors • The materials that offer very little, or no, resistance • Insulators • The materials that do not allow the current to flow • Semiconductors, • The materials that the flow of electrons can be controlled.

11. The letter R represents resistance. The unit of measurement for resistance is the ohm (Ω ).

13. Current • Electrical current is the flow of charges created when electrons move. • In electrical circuits, the current is caused by a flow of free electrons.

14. The negative terminal repels the electrons and the positive terminal attracts the electrons. • The letter “I” represents current. • The unit of measurement for current is Ampere (Amp).

15. Ohms law V = IR • Power = IV • A watt is how much power a device consumes or produces. • The current does all the work in a circuit

16. Curcuit • Curcuit : Current flows in closed loops called circuits. The circuit must be composed of conducting materials, and must have a source of voltage • Voltage causes current to flow while resistance and impedance oppose it

17. Impedance: In an AC circuit the amount of current depends on the impedance • Resistance: In a DC circuit the amount of current depends on the resistance

18. Two ways in which current flows are Alternating Current (AC) and Direct Current (DC). Alternating current (AC) and voltages vary over time by changing their polarity, or direction. AC flows in one direction.

20. Cable specifications • What speeds for data transmission can be achieved using a particular type of cable? • What kind of transmission is being considered? • How far can a signal travel through a particular type of cable before attenuation of that signal becomes a concern?

21. Some examples of Ethernet specifications which relate to cable type include: • 10BASE-T • 10BASE5 • 10BASE2

23. Coaxial cable

24. For LANs, coaxial cable offers several advantages. It can be run longer distances than shielded twisted pair, STP, and unshielded twisted pair, UTP, cable without the need for repeaters. • Coaxial cable is less expensive than fiber-optic cable, and the technology is well known

25. Poor shield connection is one of the biggest sources of connection problems in the installation of coaxial cable. • Connection problems result in electrical noise that interferes with signal transmittal on the networking media. • The metallic braid in coaxial cable comprises half the electric circuit resulting in poor grounding

26. STP cable

33. Optical Media • An important property of any energy wave is the wavelength.

34. Human eyes were designed to only sense electromagnetic energy with wavelengths between 700 nanometers and 400 nanometers (nm). • Electromagnetic energy with wavelengths between 700 and 400 nm is called visible light.

35. Wavelengths that are not visible to the human eye are used to transmit data over optical fiber • The wavelength of the light in optical fiber is either 850 nm, 1310 nm, or 1550 nm. These wavelengths were selected because they travel through optical fiber better than other wavelengths.

36. The light energy in the incident ray that is not reflected will enter the glass. • The refracted ray is the entering ray that will be bent at an angle from its original path.

37. The ratio of the speed of light in a material to the speed of light in a vacuum is called the Index of Refraction.

39. The following two conditions must be met for the light rays in a fiber to be reflected back into the fiber without any loss due to refraction:

40. The core of the optical fiber has to have a larger index of refraction (n) than the material that surrounds it. The material that surrounds the core of the fiber is called the cladding. • The angle of incidence of the light ray is greater than the critical angle for the core and its cladding

42. Optical Media

44. If the diameter of the core of the fiber is large enough so that there are many paths that light can take through the fiber, the fiber is called “multimode” fiber.

45. Single-mode fiber has a much smaller core that only allows light rays to travel along one mode inside the fiber.

46. Usually, five parts make up each fiber-optic cable. The parts are the core, the cladding, a buffer, a strength material, and an outer jacket.

47. Infrared Light Emitting Diodes (LEDs) or Vertical Cavity Surface Emitting Lasers (VCSELs) are two types of light source usually used with multimode fiber. Use one or the other. LEDs are a little cheaper to build and require somewhat less safety concerns than lasers. However, LEDs cannot transmit light over cable as far as the lasers. Multimode fiber can carry data distances of up to 2000 meters (6,560 ft).

48. The major difference between multimode and single-mode fiber is that single-mode allows only one mode of light to propagate through the smaller, fiber-optic core. The single-mode core is eight to ten microns in diameter.

49. Because of its design, single-mode fiber is capable of higher rates of data transmission (bandwidth) and greater cable run distances than multimode fiber. Single-mode fiber can carry LAN data up to 3000 meters.

50. Warning: The laser light used with single-mode has a longer wavelength than can be seen. The laser is so strong that it can seriously damage eyes. Never look at the near end of a fiber that is connected to a device at the far end. Never look into the transmit port on a NIC, switch, or router. Remember to keep protective covers over the ends of fiber and inserted into the fiber-optic ports of switches and routers. Be very careful.