Fundamentals of Electronics

Current (I)

Current is the quantity of electrons passing a given point. The unit of current is the Ampere. One Ampere is 6,280,000,000,000,000,000 electrons passing a point in one second. Electrical current flows from a region of high charge or potential to a region of low potential.

To make confusion worse there exist two notions about the direction in which current flows:

 * Conventional Current assumes that current flows out of the positive terminal, through the circuit and into the negative terminal of the source.

 * Electron Flow is what actually happens and electrons flow out of the negative terminal, through the circuit and into the positive terminal of the source.

Voltage (V or E)

Voltage is electrical pressure or force. Voltage is sometimes referred to as Potential. Voltage Drop is the difference in Voltage between the two ends of a conductor through which current is flowing.

Resistance (R)

Conductors are not perfect. They resist to some degree the flow of current. The unit of resistance is the Ohm.

Load

The part of the circuit which performs work (e.g. a motor, a light bulb or a LED, etc.) is called Load.

Ohm's Law

A set of rules that show the relationships among Current, Voltage, Power and Resistance. Given any two of the above, one is able to calculate the other two using the following formulas:

E = I x R

I = E / R

R = E / I 

P = E x I

Power (P)

        The work performed by an electrical current (or) the rate of energy consumption is called Power. The unit of Power is the watt (W)..

Power can be calculated as follows:

»P = I x E

Since E = I x R, you can also say:

»P = I2 x R

Since I = E / R, you can also say:

»P = E2 / R

Direct Current Electricity

An electrical current can flow in either of two directions through a conductor. If it flows in only one direction whether steadily or in pulses, it is called direct current (DC).

Electronics and Electronic Components

Electronics is the processing of electrical charges as information. Nam June Paik makes this distinction very clear by commenting on "electricity" and "electronics":

“Electricity deals with mass and weight,

Electronics deals with information.

One is muscle, the other is nerve."

Wires and Cables

Wires and cables are used to carry an electrical current. Most wire is protected by an insulating covering of plastic or rubber. A wire can be either solid or stranded. Cables have one or more conductors and more insulation than ordinary wire.

Diodes

A diode is an electronic device that allows current to flow through it in one direction only. It is a one-way turnstile for electrons. There are many different classes of diodes for many different purposes:

• Small signal diodes

• Rectifiers (power) diodes (e.g. in power supplies)

• switching diodes

• Zeners

• Light Emitting Diodes (LED)

Capacitors

Capacitors are electronic devices that store electrons. The simplest capacitor is two conductors separated by an insulating material called dielectric. The minus side of the capacitor is charged with electrons. These electrons in the charged capacitor will gradually leak through the dielectric until both conductor plates have an equal charge. The capacitor is then discharged. The ability to store electrons is called capacitance.

* Capacitance is specified in Farads.

Once a capacitor has reached its maximum charge, it blocks DC voltage. This is used in electronic circuits to allow an alternating current (AC) signal to flow through a capacitor while it blocks DC.

Sometimes capacitors are also used as smoothing or filtering device. Putting a capacitor across the plus and minus pole of a component filters out voltage spikes. Yet another use of capacitors makes use of their ability to store charge for high-speed use. This feature is applied for example in a photo flash.

Transistors

A transistor can be used as a switch and signal amplifier. It is an electronic device with three contacts: the emitter (E), base (B) and collector (C). A very small current on the transistor's base can control a much larger current flowing through a passage between collector and emitter.

Power transistors allow a small signal to switch a larger load. Low power transistors which do small switching functions are called signal transistors. Transistors come in several types:

• Bipolar
• Field effect (FET)
•  Uni-junction transistors, etc.

 Bipolar transistors are most commonly used, they come in two types: NPN and PNP.