The negative electrons, orbiting the positively charged nucleus of an atom, all try to get as close to the nucleus as they can. This is because opposite charges tend to attract each other. However, though no-one knows why, Quantum mechanics forces them to sit at fixed, or quantised, distances from the nucleus and only allow a limited number in each orbit level. Because of the link between the orbit and the energy, we tend to talk about the electrons sitting at various energy levels in the atom. The energy level furthest from the atom which still holds a fair number of electrons is called the valence level. This is because these are the electrons which provide most of the forces which 'stick together' solids and liquids, and control most chemical reactions. The level just above the valence level is called the conduction level. This is because electrons here help a material to be able to conduct electricity. When we remove an electron from the valence level (or one of the lower levels - nearer to the nucleus) we leave a hole. The atom now has an overall positive charge, so it looks a bit like we've added a positively charged particle to the atom. When we try to understand semiconductors, holes are very important. Engineers and solid-state physicists tend to talk about "holes moving from place to place" and "the velocity of the holes", etc. The holes don't really exist, but materials behave just as if they did. When a hole moves from atom A to atom B what actually happens is an electron moves from B to A. It looks just as though something positively charged went from A to B. 


Electricity is the movement of electrons through a conductor. Electrons are attracted to protons. Since we have excess electrons on the other end of the conductor, we have many electrons being attracted to the protons. This attraction sort of pushes the electrons toward the protons. This push is normally called electrical pressure. The amount of electrical pressure is determined by the number of electrons that are attracted to protons.

The electrical pressure or electromotive force (EMF) attempts to push an electron out of its orbit and toward the excess protons. If an electron is freed from its orbit, the atom acquires a positive charge because it now has one more proton than it has electrons. The unbalanced atom or ion attempts to return to its balanced state so it will attract electrons from the orbit of other balanced atoms. This starts a chain reaction as one atom captures an electron and another releases an electron. As this action continues to occur, electrons will flow through the conductor. A stream of free electrons forms and an electrical current is started.

This does not mean a single electron travels the length of the insulator, it means the overall effect is electrons moving in one direction. All this happens at the speed of light. The strength of the electron flow is dependant on the potential difference or voltage.

An electron hole is the conceptual and mathematical opposite of an electron, useful in the study of physics, chemistry, and electrical engineering. The concept describes the lack of an electron at a position where one could exist in an atom or atomic lattice. It is different from the positron, which is the antimatter analogue of the electron.

The electron hole was introduced into calculations for the following two situations:

1. If an electron is excited into a higher state it leaves a hole in its old state. This meaning is used in Auger electron spectroscopy (and other x-ray techniques), in computational chemistry, and to explain the low electron-electron scattering-rate in crystals (metals, semiconductors).
2. In crystals, band structure calculations lead to an effective mass for the charge carriers, which can be negative. Inspired by the Hall effect, Newton's law is used to attach the negative sign onto the charge.

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Digital circuits are electric circuits based on a number of discrete voltage levels. Digital circuits are the most common physical representation of Boolean algebra and are the basis of all digital computers. To most engineers, the terms "digital circuit", "digital system" and "logic" are interchangeable in the context of digital circuits. Most digital circuits use two voltage levels labeled "Low"(0) and "High"(1). Often "Low" will be near zero volts and "High" will be at a higher level depending on the supply voltage in use. Ternary (with three states) logic has been studied, and some prototype computers made.

Digital circuits are electric circuits based on a number of discrete voltage levels. Digital circuits are the most common physical representation of Boolean algebra and are the basis of all digital computers. To most engineers, the terms "digital circuit", "digital system" and "logic" are interchangeable in the context of digital circuits. Most digital circuits use a binary system with two voltage levels labeled "0" and "1". Often logic "0" will be a lower voltage and referred to as "Low" while logic "1" is referred to as "High". However, some systems use the reverse definition ("0" is "High") or are current based. Ternary (with three states) logic has been studied, and some prototype computers made. Computers, electronic clocks, and programmable logic controllers (used to control industrial processes) are constructed of digital circuits. Digital Signal Processors are another example.

digital circuit, electronic circuit that can take on only a finite number of states. That is contrasted with analog circuits, whose voltages or other quantities vary in a continuous manner. Binary (two-state) digital circuits are the most common. The two possible states of a binary circuit are represented by the binary digits, or bits, 0 and 1. The states are also commonly referred to as "on" and "off" or "high" and "low" (see information theory). The simplest forms of digital circuits are built from logic gates, the building blocks of the digital computer. Since most of the physical variables encountered in the real world, e.g., position and temperature, exist in analog form, they are represented electrically by continuously varying currents and voltages in analog circuits. To make digital and analog circuits compatible special converters are used-either analog-to-digital or digital-to-analog depending on the direction of information flow. Digital circuits simulate continuous functions with strings of bits; the more bits that are used, the more accurately the continuous signal can be represented. For example, if 16 bits are used to represent a varying voltage, the signal can be assigned one of more than 65,000 different values. Digital circuits are more immune to noise than analog circuits, and digital signals can be stored and duplicated without degradation (see compact disc). Digital circuits can often manipulate signals more effectively-and less expensively-than analog circuits. Those reasons helped digital systems to succeed over all analog contenders for proposed high-definition television in the United States.

A digital circuit is a circuit where the signal must be one of two discrete levels. Each level is interpreted as one of two different states (for example, on/off, 0/1, true/false). Digital circuits use transistors to create logic gates in order to perform Boolean logic. This logic is the foundation of digital electronics and computer processing. Digital circuits are less susceptible to noise or degradation in quality than analog circuits. It is also easier to perform error detection and correction with digital signals. To automate the process of designing digital circuits, engineers use electronic design automation (EDA) tools, a type of software that optimizes the logic in a digital circuit.

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Electronic vs. Electrical: For a device to be considered electronic it must meet the criteria of having a device that uses electricity to control electricity. Therefore must contain a device such as a transistor, thrysistor, etc. A device such as a desktop light with mechanical on/off switch would NOT be considered electronic, though it is considered electrical. Electronic systems are an arrangement of passive and active components with a specified input signal producing a defined output signal. Common signal processes include:

1. Amplification (magnification)
2. Integration
3. Differentiation
4. Filtering: Changing the relative magnitude of different frequency components of a signal.
5. Rectification: Selection/rejection of a particular part of a signal on polarity basis.

 Electronics is the branch of science and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits. The nonlinear behaviour of these components and their ability to control electron flows makes amplification of weak signals possible, and is usually applied to information and signal processing. Electronics is distinct from electrical and electro-mechanical science and technology, which deals with the generation, distribution, switching, storage and conversion of electrical energy to and from other energy forms using wires, motors, generators, batteries, switches, relays, transformers, resistors and other passive components. This distinction started around 1906 with the invention by Lee De Forest of the triode, which made electrical amplification of weak radio signals and audio signals possible with a non-mechanical device. Until 1950 this field was called "radio technology" because its principal application was the design and theory of radio transmitters, receivers and vacuum tubes.

physics whereas the design and construction of electronic circuits to solve practical problems come under electronics engineering. This blog focuses on engineering aspects of electronics.

Today, most electronic devices use semiconductor components to perform electron control. The study of semiconductor devices and related technology is considered a branch of solid state physics, whereas the design and construction of electronic circuits to solve practical problems come under electronics engineering. This article focuses on engineering aspects of electronics

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