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Electricity : Part 3



Continued from Electricity - Part 2...

Electric Current

It has been proven that electrons (which are negative charges) move through a conductor in response to an electric field.

Electric Current is defined as the directed flow of electrons. The direction of electron movement is from a region of negative potential to a region of positive potential. Therefore, electric current can be said to flow from negative to positive.

The direction of current flow in a material is determined by the polarity of the applied voltage.


Random Drift

All materials are composed of atoms, each of which is capable of bing ionized. If some form of energy, such as heat, is applied to a material, some electrons acquire sufficient energy to move to a higher energy level. As a result, some electrons are freed from their parent atoms, which then becomes ions. Other forms of energy, particularly light or an electric field, will cause ionization to occur.

The number of free electrons resulting from ionization is dependent upon the quantity of energy applied to a material, as well as the atomic structure of the material. At room temperature some materials, classified as conductors, have an abundance of free electrons. Under a similar condition, materials classified as insulators have relatively few free electrons.

Conductors are made up of atoms that contain loosely bound electrons in their outer orbits. Due to the effects of increased energy, these outermost electrons frequently break away from their atoms and freely drift throughout the material. The free electrons, also called mobile electrons, take a path that is not predictable and drift about the material in a haphazard manner. Consequently, such a movement is termed Random Drift.

It should be noted and emphasized that even though the degree of random drift is much greater in a conductor than it is in an insulator, that all materials still have some amount of random drift of electrons occurring within them.

Directed Drift

Every charged body will have an electrostatic field associated with it. Bodies that are charged alike will repel one another (like charges repel), while bodies with unlike charges attract each other. An electron will be affected by an electrostatic field in exactly the same manner as any negatively charged body. It is repelled by a negative charge and is attracted to or by a positive charge.

If a conductor has a difference in potential impressed across it, a direction is imparted to the random drift. This causes the mobile (free) electrons to be repelled away from the negative terminal and attracted toward the positive terminal. This results in a general migration of electrons to occur moving from one end of a conductor to the other end.

The directed migration of mobile electrons due to the potential difference is called Directed Drift.

Even though the directed movement of the electrons occur at a relatively low velocity (rate of motion in a particular direction), the effect of this directed movement is felt almost instantaneously. This is because as an electron moves into the conductor at one end, an electron is leaving the conductor at the other end at that exact same moment in time, taking place at approximately the speed of light (which is approximately 186,271.7 miles per second, which is the distance at which a photon of light travels in one second of time within a vacuum of space).


Magnitude of Current Flow

Electric current has been defined as the directed movement of electrons. Directed drift, therefore, is current and the terms can be used interchangeably. The expression directed drift is particularly helpful in differentiating between the random and directed motion of electrons. However, Current Flow is the terminology most commonly used in indicating a directed movement of electrons.

The magnitude of current flow is directly related to the amount of energy that passes through a conductor as a result of the drift action. An increase in the number of free electrons or an increase in the energy of the existing free electrons would provide an increase in current flow.

When an electric potential is impressed across a conductor, there is an increase in the velocity of the free electrons, causing an increase in the energy of them. There is also the generation of an increased number of electrons providing added carriers of energy (free electrons acting as carriers of energy). The additional number of free electrons is relatively small, and as such the magnitude of current flow is primarily dependent on the velocity of the existing free electrons motion.

The magnitude of current flow is affected by the difference of potential in the following manner. Initially, free electrons are given additional energy because of the repelling and attracting electrostatic field. If the potential difference is increased, the electric field will be stronger, the amount of energy imparted to a free electron will be greater, and the current will be increased. If the potential difference is decreased, the strength of the field is reduced, the energy supplied to the electron is diminished, and the current is decreased.


Measurement of Current

The magnitude of current is measured in Amperes.

A current of one ampere is said to flow when one coulomb of charge passes a point in one second. Remember, one coulomb is equal to the charge of 6.28 x 10^18 (that is, 6.28 times 10 to the 18th power) electrons.

Frequently, the ampere is much too large of a unit for measuring current. Therefore, the Milliampere (mA) which is one-thousandth of an ampere, or the Microampere (µA) which is one-millionth of an ampere, is used.

Most computer components and cellphone electronics actually only use a few µA or mA at any one moment of time, but over the course of an entire day then they can consume and use several Amperes (Amps) worth of current, which is why a cellphone battery that provides several Amps worth of current will only last a day or two before it needs to be recharged.

In contrast, a standard four bedroom residential house, containing a central heating and air conditioning unite, multiple ceiling fans, TV('s), lights, computer('s), Internet modems, cell phone battery recharging stations, kitchen appliances, etc... can easily consume and use several thousand Amps (several kA) per day.

Final Thoughts

Thank you for reading, I hope you found this blog post educational and helpful in some way.



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