Electricity

What is electricity?

The entity of electricity is the electron.
It is said that electricity flows from positive (+) to negative (-), but actually, electrons move from negative to positive. When this was first discovered, the world was already used to the "positive to negative" idea, so to avoid confusion, scientists introduced a more specific definition: "Current flows from positive to negative, and electrons flow from negative to positive."



Electrons are included in all substances (solids, liquids and gases). The atoms that compose a substance consist of protons (+) and neutrons that form the nucleus, and electrons (-) that surround the nucleus. Electricity is formed when the electrons of an atom are flied off by external pressure, etc. Although there ought to be the same number of protons as electrons, atoms from which electrons (-) have flown off have electrically an excess of protons (+), and so become positive ions. Conversely, atoms into which electrons (-) have entered have electrically an excess of electrons (-), and so become negative ions.

For example, the sodium atom (Na: atomic number 11) contains 11 electrons, 11 protons, and 12 neutrons.



Here, there is one electron on the outermost shell, so if this electron were to fly off, the atom would stabilize.
Another example is chlorine (Cl: atomic number 17). The chlorine atom contains 17 electrons, 17 protons, and 18 neutrons.



Here, there are seven electrons on the outermost shell, so if one electron were to enter, the atom would stabilize.
Therefore, the sodium (Na) and chlorine (Cl) atoms easily form an ion bond, and become the compound NaCl (salt). If this compound is then dissolved in water, the stable sodium Na⁺ and chlorine Cl^- ions will electrolytically dissociate (ionize), creating salt water. Sodium is an alkali metal, so water that contains the sodium ion Na⁺ is called alkali ion water.
Assuming positive or negative properties is known as "becoming charged", which means the atom has either a positive electric charge or a negative electric charge (electric charge (Q) is measured in units of coulomb [C]). The quantity of electric charge of one electron is e^- = 1.6 × 10^-19 [C].
When atoms form a compound such as in the case of salt, the electrons remain in an internally stable state; but once an electron flies off the atom, it becomes a free electron. When these electrons move to places where there are insufficient electrons, they become electric current. If there is no place for the electrons to go, and they remain in a free state, they become static electricity.
Lightening is an example of electricity in nature. Lightening occurs when electrons from negatively charged clouds (water vapor) are discharged to the earth's surface or positively charged clouds.

[Tea Break] One of the reasons electrons fly off atoms is ultraviolet rays from the sun. Ozone depletion is currently a hot topic. Ozone depletion means the destruction and loss of ozone in the stratosphere about 10 to 50 kilometers above the earth's surface (the stratosphere contains about 90% of the ozone in the atmosphere). The naked eye can see optical wavelengths of 400 to 750 nm — the colors in the rainbow (violet to red). Wavelengths longer than red are known as infrared rays and those shorter than violet are known as ultraviolet rays. Ultraviolet rays can be divided into three categories according to their effect on living organisms: UV-A (400 to 315 nm), UV-B (315 to 280 nm) and UV-C (280 to 100 nm). UV-A (A rays): These rays, most of which reach the earth's surface, cause the skin to wrinkle and sag. UV-B (B rays): These rays, only some of which reach the earth's surface, cause sunburn and skin cancer, as well as wrinkles and freckles. UV-C (C rays): These rays are the most harmful to living organisms; however they are absorbed in the ozone layer and the atmosphere, and therefore do not reach the earth's surface. Due to the destruction of the ozone layer, we are receiving the negative effect of increased exposure to UV-B. A 1% decrease in the ozone layer translates to a 1.5% increase in the amount of UV-B that reaches the earth's surface. Although the ozone layer repeatedly decays and is regenerated as part of a natural cycle, gases in the atmosphere such as chlorofluorocarbons, halons and methyl bromides react with ultraviolet rays, causing the ozone molecules to break up. This leads to the destruction of the ozone layer. The reason this destruction is occurring so rapidly is that a single chlorine or bromine atom can react chemically with ozone causing a chain reaction that breaks up thousands of ozone molecules. Take chlorofluorocarbons for example. Chlorofluorocarbons are compounds that consist of carbon, hydrogen, fluorine, chlorine, etc. (a certain group of chlorofluorocarbons is also known internationally as Freon, a trade name of DuPont). If a chlorine molecule is released from a chlorofluorocarbon molecule that has been broken up by ultraviolet rays and comes into contact with an ozone molecule, the following catalyzed reaction will occur. Cl2 + 2O3→2ClO + 2O2→Cl2 + 3O2 In other words, two ozone molecules (2O3) become three oxygen molecules (3O2), effectively causing the ozone molecules to disappear. Since ozone has very strong antibacterial properties and does not pollute the environment, it is often used in disinfecting systems. But is it really good for us? Ozone (O3) is bonded after oxygen (O2) is broken up by ultraviolet rays. In other words, ozone is a type of radical oxygen (free radical). Although free radicals are generated in our bodies, a large amount of them may cause cancer. We want to keep protected from ultraviolet rays by Ozone which is in the stratosphere in the future.

(2006/03)

Please explain the meanings of the units used to measure electricity.

The basic parameters used for quantifying electricity are voltage (V; unit: volts [V]), current (I; unit: amperes [A]), resistance (R; unit: ohms [Ω]), power (P; unit: watts [W]) and frequency (F; unit: hertz [Hz]).

(1)Voltage
Voltage is the potential energy of an electric charge. Consequently, the degree of voltage is expressed as high or low. Taking water as an example, the water pressure becomes higher at the deeper point in the water, and the energy of the water flow becomes greater when the gap between the high and low positions is larger.
When voltage is added to a substance, it is known as "applying voltage".
Note that in terms of electricity, there are two types of current: alternating current (AC), in which the polarity (±) changes over time, and direct current (DC), in which the polarity does not change. In Japan, a 100 V AC home power line uses alternating current in the form of a sine wave and has an RMS (root mean square) value of ±100 V, with a peak value of ±141 V. On the other hand, the output of a power supply adapter is direct current, such as a value of 4.5 V DC.



Voltage is a relative concept. For example, when supplying power between the V_DD and GND pins of a semiconductor IC, considering that GND = 0 V, V_DD = 3.3 V means that a voltage that is 3.3 V higher than GND is applied. Absolute voltage is defined as potential which is difference from ground being 0 V. The GND in the previous example is the potential of the equipment's chassis (chassis ground), which is not necessarily 0 V potential being earth ground. The voltage between two points is the difference in potential, and voltage, which is a generally used term, refers to such difference in potential.





(2)Current
Current expresses the amount of electricity (electric charge: Q) flowing per unit time.

Current I = dQ/dt

The higher the voltage, the larger the amount of current.



A 1 A current passing through the human body is said to be fatal. This 1 A current can be illustrated as follows.

A force of 2 × 10^-7N (Newton) per meter exists between two 1 A currents that travel in parallel at a distance to each other of 1 meter.

The terms "current consumption" and "to consume current" are incorrect. (See (4) Power.)

(3)Resistance
Resistance indicates how difficult it is for current to flow. Even when the voltage is the same, the lower the resistance, the larger the amount of current that flows.



Ohm's law is one of the fundamental principles of electricity.

Ohm's law: Voltage V (V) = Current I (A) × Resistance R (Ω)

(4)Power
Power is the value of voltage multiplied by current.

Power P (W) = Voltage V (V) × Current I (A)

For example, a current of 0.4 A (= 40 ÷ 100) flows to a 40 W light bulb in a lamp connected to a 100 V AC home power line in Japan.
In the statement you receive from your power company, you'll notice they use the unit "kWh". This is the integral power consumption; i.e., an accumulation of the power consumed per hour. For example, a 40 W light bulb used for one hour would consume 40 Wh of power, and a 1500 W heater used for three hours would consume 4.5 kWh of power.
Note that the term "consume" is used when referring to the amount of power used. The term "current consumption" is a misnomer because current is not "consumed", i.e., it either loops around to its source or arrives at a certain destination. In principle, the term consumption should only be used for power (power consumption). Current should be referred using terms such as "rated current", "power supply current", and "operating current".

[Tea Break] The common practice is to obtain an average value for changes on the time axis as the power value in the case of AC electricity. The effective value refers to the notation method for the voltage and current consuming the same average power as DC, when supplying AC current to resistance load R. The power value at each instant using AC current i(t) is expressed as Ri(t)2and the average value is the average of Ri(t)2, with DC current I defined as follows. Based on this relationship, the effective value is expressed as the root of the mean of the square of that instant value. From this, Vrms and Irms use the subscript "rms" (root mean square) to indicate the fact that the value is the effective value. In this manner, alternating current voltage and current are expressed as effective values, which makes it possible to perform power calculations in the same way as for DC. Let us perform calculations using a sine wave of alternating current with peak voltage and current values Vp and Ip. Current i(t) = Ip · sinωt Voltage v(t) = R · Ip · sinωt Power P(t) = R · i(t)2 = R · Ip2 · sin2ωt = R · Ip2 · (1/2)(1-cos2ωt) The average power consumption is calculated by integrating the value of one period T and dividing the result by the period T. ωt for one period is 2π, and the second term becomes 0 after integration. Therefore: The equation for calculating the direct current is P = V · I Therefore, by defining Vrms and Irms (RMS values) as Vp and Ip divided by the square root of 2, the expression becomes the same as that for direct current.

(5)Frequency
Frequency refers to the number of oscillations per second in an alternating current element that changes with a fixed period. The frequency and period have an inverse relationship.

Frequency f (Hz) = 1/period T (s)

[Tea Break] In Japan, the frequency of commercially transmitted power is 50 Hz in eastern Japan and 60 Hz in western Japan. This is an anomaly that occurred due to the difference of power generator introduced in each region. In 1883, the year after Thomas Edison created the world's first power supply system, the Tokyo Electric Light Company (currently The Tokyo Electric Power Company (TEPCO)) was established and, riding the wave of cultural enlightenment, pushed for the complete electrification of Japan. Initially, Tokyo used direct current and Osaka alternating current. However, in 1895, Tokyo also switched to alternating current, and a 50 Hz alternating current generator from a German company, Allgemeine Elektrizitaets Gesellshaft (AEG), was installed at the thermal power station in Asakusa. The Osaka Electric Light Company, on the other hand, first purchased a 125 Hz generator from an American company, Thomson-Houston (which later merged with General Electric (GE)), but switched to a GE 60 Hz generator in 1897. Subsequently, the electric power companies in Kobe, Kyoto and Nagoya also started using GE 60 Hz generators. This is why the frequency of power in western Japan became 60 Hz. When an alternating current motor is used in 50 Hz and 60 Hz systems, the number of revolutions differs 20% since the motor revolution is frequency-dependent, and a function to switch the frequency would be then required. For example, the Tokaido railway line switches frequencies when it passes the Fuji River. Recently, however, the increasing use of DC motors and inverter control has reduced the need to worry about frequency issues.

(2007/11)