ElectricityFundamentals


By Maduranga Jayasinghe | 2017, August 31  Views : 213












මෙම පිටුව යාවත්කාලීන කරමින් පවතී...











To put it simply, Electricity is the movement of electrons from through a conductor. More specifically, Electricity is a type of energy that can build up in one place or flow from one place to another. When electricity gathers in on place it is known as Static Electricity (the word static means something that does not move). Electricity that move from one place to another is called Current Electricity.

♔ Static Electricity


Static electricity often happens when you rub things together. If you could go back to your school period, you would remember that you have done some scientific things for fun in your science laboratory or class room. Have you ever rubbed a balloon against your pullover 30 or 40 times and have you see what happens? you can find the balloon stick to you. How this happens? This happens because rubbing the balloon gives it an electric charge(a small amount of electricity). That charge makes it stick to your pullover like a magnet, because your pull over gains an opposite electric charge. So your pullover and the balloon attract one another like the opposite ends of two magnets.

Have you ever felt a sharp pain in your hand when touch something metal like a door knob? That is an example of an Electric Shock. When you touch metal, the charge runs instantly to Earth and that's the shock you feel. When you handling electronic circuit board you must be more careful. Circuit boards are made up of very sensitive components, and handling them with naked hand is an almost surefire way of ensuring the board is damaged. Putting pressure on one of the small components can cause serious damage, while even a small amount of static electricity can completely destroy the board. The best way to prevent damage to a circuit board is by keeping the possible generation of static electricity to a minimum, discharging any static electricity that has built up and handling the circuit with care.

Put on rubber soled shoes to ground yourself prior to handling a circuit board. This helps prevent a buildup of static electricity that could severely harm the board. Touch a piece of metal for two seconds before handling the circuit to discharge any residual electricity stored in your body.

♔ Current electricity


When electrons move, they carry electrical energy from one place to another. This is called current electricity or an electric current. A lightning bolt is one example of an electric current, although it does not last very long. Electric currents are also involved in powering all the electrical appliances that you use, from washing machines to flashlights and from telephones to MP3 players. These electric currents last much longer.

Have you heard of the terms potential energy and kinetic energy? Potential energy means energy that is stored somehow for use in the future. A car at the top of a hill has potential energy, because it has the potential (or ability) to roll down the hill in future. When it's rolling down the hill, its potential energy is gradually converted into kinetic energy (the energy something has because it's moving). 

Static electricity and current electricity are like potential energy and kinetic energy. When electricity gathers in one place, it has the potential to do something in the future. Electricity stored in a battery is an example of electrical potential energy. You can use the energy in the battery to power a flashlight, for example. When you switch on a flashlight, the battery inside begins to supply electrical energy to the lamp, making it give off light. All the time the light is switched on, energy is flowing from the battery to the lamp. Over time, the energy stored in the battery is gradually turned into light (and heat) in the lamp. This is why the battery runs flat.

♔ Electric circuits


For an electric current to happen, there must be a circuit. A circuit is a closed path or loop around which an electric current flows. A circuit is usually made by linking electrical components together with pieces of wire cable. Thus, in a flashlight, there is a simple circuit with a switch, a lamp, and a battery linked together by a few short pieces of copper wire. When you turn the switch on, electricity flows around the circuit. If there is a break anywhere in the circuit, electricity cannot flow. If one of the wires is broken, for example, the lamp will not light. Similarly, if the switch is turned off, no electricity can flow. This is why a switch is sometimes called a circuit breaker.

You don't always need wires to make a circuit, however. There is a circuit formed between a storm cloud and the Earth by the air in between. Normally air does not conduct electricity. However, if there is a big enough electrical charge in the cloud, it can create charged particles in the air called ions (atoms that have lost or gained some electrons). The ions work like an invisible cable linking the cloud above and the air below. Lightning flows through the air between the ions.

♔ How electricity moves in a circuit


All the solid-state materials that don't allow electricity to pass through. These materials can be classified into three groups.

    1.  insulators
    2. conductors
    3. semiconductors

1.) insulators

The materials that electricity cannot pass is called insulators. Plastic, glass, wood etc are the example of insulators.

2.) conductors

Most of the conductors used in electronics are metals like copper, aluminium and steel. Conductors are materials that obey Ohm's law and have very low resistance. They can therefore carry electric currents from place to place without dissipating a lot of power. As a result, metals are useful as connecting wires to carry electrical signals from place to place. They help ensure that most of the signal's power reaches it's destination instead of warming up the wires in between!

In fact, although it sounds odd, modern resistors are also made of conductor materials. However, they use very thin pieces of conductor which don't pass current too easily.

3.) semiconductors

All the transistors, diodes, integrated circuits, etc. used in modern electronics are built using a range of semiconductors. The basic property of a semiconductor is given away by its name - it 'conducts a little bit'. A semiconductor will carry electric current, but not as easily as a normal conductor.

♔ Difference between Conductor Semiconductor and Insulator


CHARACTERISTICS
INSULATOR
CONDUCTOR
SEMI-CONDUCTOR
ConductivityLowHighModerate
ResistivityVery HighLowModerate
Forbidden gapLarge forbidden gapNo forbidden gapSmall forbidden gap
Temperature coefficientNegativePositiveNegative
ConductionModerate number of electrons for conductionLarge number of electrons for conductionVery small number of electrons for conduction
Conductivity valueNegligible like 10-13mho/m10-13mho/mVery high 10-7mho/m10-7mho/mBetween those of conductors and insulators i.e. 10-7mho/m10-7mho/m to 10-13mho/m10-13mho/m
Resistivity valueVery high; more than 105 Ω-m105 Ω-mNegligible; less than 10-5 Ω-m10-5 Ω-mBetween those of conductors and insulators i.e. 10-5 Ω-m10-5 Ω-m to 105 Ω-m105 Ω-m
Current flowDue to negligible free electronsDue to free electronsDue to holes and free electrons
Number of current carriers at normal temperatureNegligibleVery highLow
Band overlapBoth bands are separated by an energy gap of 6eV to 10eVBoth conduction and valence bands are overlappedBoth bands are separated by an energy gap of 1.1eV
0 Kelvin BehaviorActs like an insulatorActs like a superconductorActs like an insulator
FormationFormed by ionic bondingFormed by mettalic bondingFormed by covalent bonding
Valence ElectronsEight valence electron in outermost shellOne valence electron in outermost shellFour valence electron in outermost shell
ExamplesWood, Rubber, Mica, PaperCopper, mercury, aluminum, silverGermanium, Silicon

♔ Electrical Voltage ( V )


Voltage, ( V ) is the potential energy of an electrical supply stored in the form of an electrical charge. Voltage can be thought of as the force that pushes electrons through a conductor and the greater the voltage the greater is its ability to “push” the electrons through a given circuit. As energy has the ability to do work this potential energy can be described as the work required in joules to move electrons in the form of an electrical current around a circuit from one point or node to another.

img:(Voltage Symbols)

♔ Electrical Current ( I )


Electrical Current, ( I ) is the movement or flow of electrical charge and is measured in Amperes. It is the continuous and uniform flow (called a drift) of electrons (the negative particles of an atom) around a circuit that are being “pushed” by the voltage source. In reality, electrons flow from the negative (-ve) terminal to the positive (+ve) terminal of the supply and for ease of circuit understanding conventional current flow assumes that the current flows from the positive to the negative terminal.

Generally in circuit diagrams the flow of current through the circuit usually has an arrow associated with the symbol, I, or lowercase i to indicate the actual direction of the current flow. However, this arrow usually indicates the direction of conventional current flow and not necessarily the direction of the actual flow

1. Conventional Current Flow

Conventionally this is the flow of positive charge around a circuit, being positive to negative. The diagram at the left shows the movement of the positive charge (holes) around a closed circuit flowing from the positive terminal of the battery, through the circuit and returns to the negative terminal of the battery. This flow of current from positive to negative is generally known as conventional current flow.

(IMG)
2. Electron Flow

The flow of electrons around the circuit is opposite to the direction of the conventional current flow being negative to positive.The actual current flowing in an electrical circuit is composed of electrons that flow from the negative pole of the battery (the cathode) and return back to the positive pole (the anode) of the battery.

(IMG)

♔ Resistance ( R )


Resistance, ( R ) is the capacity of a material to resist or prevent the flow of current or, more specifically, the flow of electric charge within a circuit. The circuit element which does this perfectly is called the “Resistor”.

Resistance is a circuit element measured in Ohms, Greek symbol ( Ω, Omega ) with prefixes used to denote Kilo-ohms ( kΩ = 103Ω ) and Mega-ohms ( MΩ = 106Ω ). Note that resistance cannot be negative in value only positive.
(IMG)

♔ Power


Power (P) represents the work performed by an electrical current.

♔ Simulation


1. Power Drain

If you had a water tower with a nozzle on it that released water on to a turbine which spins then : Voltage = the amount of water in the tower, Current = The amount of water passing from the nozzle, Resistance = The size of the nozzle, Power = The spinning of the turbine. Power is drain with time. For example, Suppose that you are using your fully charged laptop without connect to the power supply. With the time it drain its power.

(IMG)

2. Recharge and Consume

After power drain, you can close the tap re-fill the tank and use the power again to spin the turbine. For example, After drain you laptop battery suppose that you shutdown your laptop connected to the power supply for charging. After completing, you can use the power until it drain.

(IMG)

3. Consume Power While Charging

You can fill the tank with water while spinning of the turbine. This will continue the constant power until you close the water supply to the tank. Some thing like this happen while you use laptop connected to the power supply.

(IMG)

♔ Resistor


A resistor reduce the flow of current and voltage. You can figure out their value by turning them so the gold or silver strip is on the right. Silver means the value is accurate within 10%. Gold means it is accurate to within 5%. If there is no gold or silver strip turn the resistor so that the strips are on the left side. 


Some resistors have an additional strip that provides for more accuracy and in that case the 4th strip represents the number of zeros.












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