basic elebasic electricity

7/29/2019 Basic EleBasic Electricity

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Current : Charge is mobile and can flow freely in certain materials, called conductors.Metals and a few other elements and compounds are conductors. Materials that chargecannot flow through are called insulators. Air, glass, most plastics, and rubber areinsulators, for example. And then there are some materials called semiconductors, thatseemed to be good conductors sometimes but much less so other times. Silicon andgermanium are two such materials.

There is a force between them, the potential for work, and thus a voltage. Now weconnect a conductor between them, a metal wire. On the positively charged sphere,positive charges rush along the wire to the other sphere, repelled by the nearby similarcharges and attracted to the distant opposite charges. The same thing occurs on theother sphere and negative charge flows out on the wire. Positive and negative chargescombine to neutralize each other, and the flow continues until there are no chargedifferences between any points of the entire connected system.

There may be a net residual charge if the amounts of original positive and negativecharge were not equal, but that charge will be distributed evenly so all the forces arebalanced. If they were not, more charge would flow. The charge flow is driven by voltageor potential differences. After things have quieted down, there is no voltage differencebetween any two points of the system and no potential for work. All the work has beendone by the moving charges heating up the wire.

Current


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The flow of charge is called electrical current. Current is measured in amperes (a),amps for short (named after another French scientist who worked mostly withmagnetic effects).

An ampere is defined as a flow of one Coulomb of charge in one second past somepoint. While a Coulomb is a lot of charge to have in one place, an ampere is acommon amount of current; about one ampere flows through a 100 watt

incandescent light bulb, and a stove burner or a large motor would require ten ormore amperes. On the other hand low power digital circuits use only a fraction of anampere, and so we often use units of 1/1000 of an ampere, a milliamp, abbreviatedas ma, and even 1/1000 of a milliamp, or a microamp, a .

Two spheres with opposite charges are connected by a conductor, allowing charge to flow


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A resistor is an electrical component that limits or regulates the flow ofelectrical current in an electronic circuit. Resistors can also be used toprovide a specific voltage for an active device such as a transistor.

Resistor


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A capacitor (formerly known as condenser) is a passive two-terminal electrical component used to store energy in an electric field. Theforms of practical capacitors vary widely, but all contain at leasttwo electrical conductors separated by a dielectric (insulator); for example,one common construction consists of metal foils separated by a thin layer ofinsulating film. Capacitors are widely used as parts of electrical circuits in

many common electrical devices.

Capasitor


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A transistor is a semiconductor device used to amplify and switch electronic signalsand power. It is composed of a semiconductor material with at least three terminalsfor connection to an external circuit. A voltage or current applied to one pair of thetransistor's terminals changes the current flowing through another pair of terminals.Because the controlled (output) power can be much more than the controlling(input) power, a transistor can amplify a signal. Today, some transistors are packaged

individually, but many more are found embedded in integrated circuits.

Transistor

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