Review of UNits

UNits of Measurement

This course will analyze fundamental systems in computing and telecommunications. These systems operate in the physical world and are subject to the principals of physics and electromagnetism. These fundamental scientific and engineering concepts, therefore, require us to speak a common language. Having a good understanding of basic units, scaling, and prefixes is important to the study of cyber engineering.

Electrical/Computer/Cyber Engineering is a profession that deals with the study, design, and application of devices and systems that utilize electricity, electrons, and electromagnetism. Electrical and Computer Engineers are involved in developing technologies such as: cell phones, computers, motors, generators, batteries, the power grid, robots, video games, electric cars, ships, aircraft, and more.

This page is meant as a review of concepts from SY110 (Cyber 1) and SP212 (Physics 2).

Scaling & PrefIxes

The SI system is a universally accepted standard for scientific measurements. It ensures uniformity and accuracy in expressing physical quantities. An integral part of this system is the use of prefixes, which modify the magnitude of base units, making it easier to handle very large or very small numbers.

Understanding Proportions: Recognize that each prefix represents a power of ten. This exponential relationship aids in quick conversion and calculation.
Comparing Magnitudes: Use prefixes to compare the sizes of different quantities efficiently. This provides a clear understanding of how one quantity relates to another in terms of scale.

https://www.nist.gov/pml/owm/metric-si-prefixes

Time and Frequency

A unit of time refers to any specific time interval, used as a standard way of measuring or expressing duration. The base unit of time in the International System of Units (SI), and by extension most of the Western world, is the second [s].

The number of periods or cycles per second is called frequency (f). The SI unit for frequency is the hertz [Hz]. One hertz is the same as one cycle per second.

Common in the study of telecommunications and cyber engineering, is the analysis of electromagnetic waves. We will see this a lot in this course. The wave (as in physics) can be modeled as a sinusoid and can be expressed in either time or space. An example of a wave in time is below, where the distance between peaks is a time period (T) and measured in the SI unit of seconds.

Space

A unit of length refers to any arbitrarily chosen and accepted reference standard for measurement of length. The base unit in the International System of Units (SI) is the meter [m], defined as "the length of the path travelled by light in vacuum during a time interval of 1⁄299792458 seconds.

Below is an example of an electromagnetic wave in space, where the distance between peaks is the wavelength and is measured in the SI unit of distance, the meter. Because a wave can be expressed in either time or space, we have to be able to convert between these dimensions. To do this we use the speed at which energy travels in the electromagnet spectrum, the speed of light. All forms of electromagnetic radiation, including visible light, travel at the speed of light, commonly denoted c, which is a universal physical constant that is exactly 299,792,458 meters per second or approximately 3x10^8 m/s.

Energy

Electric Charge:

What is electric charge? Electric charge is the property of fundamental particles (electrons, protons, and neutrons) that determines how they react to electric and magnetic fields. Electric charge is expressed in units of Coulombs (C).

Voltage:

What is voltage? Voltage is the amount of work required to move an electric charge from some reference point to another point in space. Voltage is expressed in units of Volts (V). To better comprehend voltage, consider another phenomenon: magnetic attraction. The North pole of one magnet is attracted to the South pole of another magnet, just as positive electric charges are attracted to negative electric charges. As you have likely experienced, it takes some effort to pull two magnets apart and, likewise, it takes some effort to pull a positive and negative charge apart. The amount of effort, or work, required to pull the negative charge away from the positive charge is what we call voltage.

Current:

What is current? Current is the rate at which electrical charges move (or flow) through an area. Current is expressed in units of Amperes or Amps (A). Just as we might measure the rate at which water flows through a sluice gate, we can also measure electric charges in the same way.

Power

Power is the amount of energy transferred or converted per unit time. In the International System of Units, the unit of power is the watt, equal to one joule per second.

Power vs. Energy:

Recall that the power supplied/consumed by something is equivalent to the amount of energy supplied/consumed by the same thing, but over a period of time : so, Power = Energy/Time.

Power gain of an electrical network is the ratio of an output power to an input power.

Communication systems transmit electrical (EM) signals to convey information. The strength of a signal is based on its electrical power, and the transmit power is an important consideration in how far a signal can be transmitted through the atmosphere. In addition, the received power is important factor in how accurately an information signal can be recovered; if the received power is not high enough to overcome the noise present, then information will be lost.

Decibels

As engineers, we just want our lives to be as easy as possible. So rather than work with these terribly tedious numbers, we often convert the numbers into decibels (dB). The decibel is a logarithmic measure that provides more convenient gain and attenuation values by changing them to a logarithmic scale. The benefit of a log scale is that it can map a very large range of decimal values into a small range of decibel values.

To convert a decimal value X into decibel value XdB use the following rule:

If X is a value greater than 1.0, then XdB will be a positive value, and if X is a value less than 1.0, XdB will be a negative value. The decibel value of zero is negative infinity, and the decibel is undefined for negative values.