Wave Propagation and Types of Wave Motion Quiz

Study Notes

Three primary characteristics of electromagnetic waves are:
- Wave velocity
- Frequency (the rate at which the wave repeats itself)
- Wavelength (distance of one cycle)

λ = c / f
- where λ is the wavelength (meter per cycle)
- c is the velocity of light (3 x 10^8 m/s)
- f is the frequency (hertz)

Balanced transmission lines:
- Have two wires, both conductors carry current
- One conductor carries signal while the other is a return path
- Signal that travels in opposite direction (metallic circuit current)
- Signal that travels in the same direction (longitudinal current)
Unbalanced transmission lines:
- One wire is at ground potential, other wire at signal potential
- Advantage: Requires only one wire for each signal
- Disadvantage: Less immunity to noise

Comprised of two or more metallic conductors separated by non-conductive insulating material (dielectric)
- Examples: air, rubber, propylene

It is the current level, not the voltage, that is responsible for effects
According to Ohm's Law, a certain voltage is required to cause the necessary currents to flow
Values vary depending on the body

Open Wire Transmission Line:
- Two parallel wires, closely spaced, separated by air
- Distance between two conductors is generally between 2 to 6 inches
- Dielectric is air
- Radiation losses are high
- Crosstalk is present
- Used for standard voice grade telephone
Twin Lead Transmission Line:
- Same as open wire transmission line, except the insulating material is a solid dielectric
- Commonly used to connect TV to rooftop antenna
Twisted Pair Transmission Line:
- Formed by twisting two insulated conductors around each other
- Mostly stranded in units, the units are cabled into cores containing up to 3000 pairs of wire
- Covered by sheaths
- Neighboring pairs are sometimes twisted with different pitches to reduce EMI and RFI from external sources
- The higher the gauge, the smaller the diameter and the higher the resistance
- Twisting the wires also reduces crosstalk between cable pairs
- Used in telephone networks
- Simple to install and relatively inexpensive

Propagation: movement through a medium
Wave: disturbance that moves through a medium
Wave motion: recurring disturbance advancing through space with or without a medium
Wave propagation: the travel of electromagnetic waves or sound waves through a medium, or the travel of a sudden electric disturbance along a transmission line

Transverse waves: travels at right angles to the direction of propagation
Longitudinal waves (compression waves): travels back and forth in the same direction as the wave motion

Two categories:
- Guided (wired system): uses conductor that provides a conduit in which electromagnetic signals are contained
- Unguided (wireless system): emitted then radiated through air or a vacuum
Examples:
- Guided: copper cables, pair of wire, coaxial cable, fiber optic
- Unguided: Earth's Atmosphere, Free Space (Vacuum)

Transmission media: something (solid, liquid, gas, or plasma) that can transmit energy
Transmission line: metallic conductor system that is used to guide or transfer electrical energy from one point to another
Metallic transmission lines: metallic conductor system used to transfer electrical energy from one point to another using electrical current flow
Transverse Electromagnetic Waves (TEM): a TEM propagates primarily in non-conductor (dielectric) that separates the two conductors