Electrical Energy
It is important to notice that no work is accomplished unless the force applied causes a change in the position of a stationary object or a change in the velocity of a moving object.
Energy
energy as the ability to do work.
The energy contained by an object due to its motion is called kinetic energy.
The energy contained by an object due to its position is called potential energy.
Electrical Charges
The practical unit adopted for measuring charges is the coulomb, named after the scientist Charles Coulomb. One coulomb is equal to the charge of 6,280,000,000,000,000,000 (six quintillion two hundred and eighty quadrillion) or 6.28 x 10^18 electrons. When a charge of one coulomb exists between two bodies, one unit of electrical potential energy exists, which is called the difference of potential between the two bodies. This is referred to as electromotive force, or voltage, and the unit of measure is the volt.
however, one body is deficient of 6 coulombs(representing 6 volts), and the other is deficient by 12 coulombs (representing 12 volts), there is a difference of potential of 6 volts. The body with the greater deficiency is positive with respect to the other.
the potentials at various points in a circuit are generally measured with respect to the metal chassis on which all parts of the circuit are mounted. The chassis is considered to be at zero potential and all other potentials are either positive or negative with respect to the chassis. When used as the reference point, the chassis is said to be at ground potential.
When a difference in potential exists between two charged bodies that are connected by a conductor, electrons will flow along the conductor. This flow is from the negatively charged body to the positively charged body until the two charges are equalized and the potential difference no longer exists.
An analogy of this action is shown in the two water tanks connected by a pipe and valve in figure
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| An analogy of the potential difference |
A fundamental law of electricity is that the electron flow is directly proportional to the applied voltage. If the voltage is increased, the flow is increased. If the voltage is decreased, the flow is decreased.
Electric Current
Electron flow
The direction of electron movement is from a region of negative potential to a region of positive potential.
Conventional Current Flow
In the UK and Europe, conventional current flow is said to be from positive to negative potential - the opposite way to the actual flow of electrons.
Random Drift
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 drifts about the material in a haphazard manner. Consequently, such a movement is termed random drift.
It is important to emphasize that the random drift of electrons occurs in all materials. The degree of random drift is greater in a conductor than in an insulator.
Directed Drift
The directed migration of mobile electrons due to the potential difference is called directed drift.
The magnitude of Current Flow
Electric current has been defined as the directed movement of electrons.
current flow is the terminology most commonly used in indicating a directed movement of electrons.
If the potential difference is increased, the electric field will be stronger, the amount of energy imparted to a mobile 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 the 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 electrons.
The device used to measure current is called an ammeter.
Electrical Resistance
A conductor has one ohm of resistance when an applied potential of one volt produces a current of one ampere. The symbol used to represent the ohm is the Greek letter omega (Ω).
Conductance
The term that is the opposite of resistance is conductance. Conductance is the ability of a material to pass electrons. The factors that affect the magnitude of resistance are exactly the same for conductance, but they affect conductance in the opposite manner.
The unit of conductance is the mho (G), which is ohm spelled backward. Recently the term mho has been redesigned siemens (S).
Electrical Laws
Faraday's Law
Faraday's law of induction states that the induced electromotive force in a closed loop of wire is directly proportional to the time rate of change of magnetic flux through the loop.
Ohm's Law
An electrical circuit, the current passing through a conductor between two points is directly proportional to the potential difference (i.e. voltage drop or voltage) across the two points, and inversely proportional to the resistance between them.
Kirchhoff's Laws
Current Law
At any point in an electrical circuit where charge density is not changing in time, the sum of currents flowing towards that point is equal to the sum of currents flowing away from that point.
Voltage Law
The directed sum of the electrical potential differences around any closed circuit must be zero.
Lens's Law
The induced current in a loop is in the direction that creates a magnetic field that opposes the change in magnetic flux through the area enclosed by the loop. That is, the induced current tends to keep the original magnetic flux through the field from changing.
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