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conceptual questions on semiconductor physics
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A Semiconductor Device
A semiconductor device which conducts electric current run in one direction only. This is the simplest kind of semiconductor device, it has two terminals and a single PN junction. One diode can be used as a half-wave rectifier or four as a full-wave rectifier.
electron tube, evacuated glass or metal envelope containing two electrodes, a cathode and an anode. It is used as a rectifier and as a detector in electronic circuits such as radio and television receivers. When a positive voltage is applied to the anode (or plate), electrons emitted from the heated cathode flow to the plate and return to the cathode through an external load. If a negative voltage is applied to the plate, electrons cannot escape from the cathode and no plate current flows. Thus a diode permits electrons to flow from the cathode to the plate, but not from plate to cathode. If an alternating voltage is applied to the plate, current flows only during the time when the plate is positive. The alternating voltage is said to be rectified, or converted to dc (direct current).
In the indirectly heated cathode type of tube shown in the illustration, the electron emitter consists of a metallic cylinder, usually nickel, coated with an electron emitter, such as a mixture of barium and strontium oxides. The heat is provided by a coil of wire (heater) located inside the sleeve but insulated from it. In the directly heated cathode (right), the heater wire itself serves as the source of electrons and is referred to as the filament.
Solid-state rectifiers, which have largely replaced the vacuum type, are also frequently referred to as diodes.
Here's a simple guide to understanding diode characteristics and their use in circuit design.
Although diodes have been around for many years, few hobbyists truly understand how the devices operate, nor are they aware of the many applications to which these little "globs of grease" are suited and so they are ill equipped to take full advantage of their various "talents." So what we'll attempt to do in this space is set you on the road to enlightenment. We won't get into the composition of the device, but instead concentrate on biasing characteristics as they relate to circuit design. But, before we begin any discussion of diode circuit design, we must first discuss current flow. That's because semiconductor diodes are much easier to control with a bias current, than with a bias voltage.
Answer: The term thermiionic emission comes from the phenomena of quantumm mechanical tunneling which takes place in some special circumstances. It sometimes happens that electrons with energy less than the barrier height to cross the barrier passing through it instead of over is called tunnneling effect. In semi conductors we can see this in heavily doped material where the current in the forward direction arises due to tunneling of the charged particles with energies close to the Fermi level but not the actual barrier height. This kind of emission due to tunneling is called field emission. Now if we increase the forward bias voltage, the electrons acquire enough energy to tunnel through the thin depletion region. To avoid this kind of tunneling and get a pure current flow we raise the temperature to a certain point such that the electrons get enough energy to cross the barrier and no longer tunnel through it. This temperature generated effect is called pure thermionic emission.
Measured the charge of an electron. The charge of one electron is known as the elementary charge.
Electrolyte can be defined as the aqueous or molten substances which when dissolved in a solvent dissociates into ions and can transmit negatively charged ions.
where the electrons are forced to travel an alternate route to reach the hydrogen and oxygen. By
*an electrical device which converts an alternating current into a direct one by allowing a current to flow through it in one direction only.
“A cathode is the electrode from which a conventional current leaves a polarized electrical device.”
To understand how this electricity works we must start with the basics. The atom is the smallest unit of matter, consisting of protons, neutrons, and electrons. Protons have a positive charge, neutrons have no charge, and electrons have a negative charge. Electric charges that are the same repel each other and charges that are different attract each other. Electric charges can exist alone, unlike magnetic poles.
Converting light energy to heat energy: Solar cooker will concentrate sunlight onto the evacuated tube. The interaction between the
A battery is a device which converts chemical energy into electrical energy. A battery usually consists of two or more cells connected in series or parallel, you can also have a single cell battery. All cells consist of a positive electrode, and a negative electrode. An electrolyte is a liquid substance capable of conducting electricity. In this substance one of the electrodes will react producing electrons, while the other will except electrons. When the electrodes are connected to a device to be powered, called a load, an electrical current flows.
For years scientists had known that if an electric current was passed through a vacuum tube, a stream of glowing material could be seen, however no one could explain why. Thomson found that the mysterious glowing stream would bend toward a positively charged electric plate. Thomson had the idea, and was later proven correct that the stream was in fact made up of small particles, pieces of atoms
can pick up vibration from an atom in a hot part of the metal. The
Diodes are basic semiconductor devices that will only allow current to flow through them in one direction only, Forward bias. Diodes are made from two differently doped layers of semiconductor material that form a PN junction. When the diode is reverse biased, the positive holes are attracted towards the negative voltage and away from the junction. Likewise the negative electrons are attracted away from the junction towards the positive voltage applied to the cathode. As higher voltages are applied in reverse polarity to the diode, the depletion layer becomes wider as the applied voltage is attracting more charge carriers away from it. The diode will not conduct with a reverse voltage when a reverse bias applied. Once the voltage is applied in the forward direction, current will flow; in this case as the voltage is increased more current flows.
When we place two objects with different temperatures in contact with each other, the heat from the hotter object will immediately and automatically flow to the colder object. This is known as conduction. Some objects make excellent conductors of heat while others make poor conductors of heat or excellent insulators. Silver, copper, and gold make excellent conductors of heat. Foams and plastics make good insulators of heat but make poor conductors. Last night for dinner, I made myself a grilled cheese sandwich and a bowl of tomato soup. I heated the soup faster than I cooked the sandwich so I poured the hot soup into a bowl and finished cooking the sandwich. Once I was done cooking, I gabbed the soup bowl and burned my hand. The heat from the soup made the bowl hot. This is an example of conduction.
Direct current only flows in one direction in a circuit. Because the polarity of a direct current voltage source is always the same the flow of current never changes direction. Batteries are one of the more common direct current voltage sources. Batteries are good because their voltage is fixed as well as their polarity. Direct current dose not always need to a constant voltage but it must always stay traveling in the same direction. There are such direct currents called varying and pulsating that change value but not direction.
A tesla coil is a high frequency and an air core transformer. The coil was created by Serbian American Physicists Nikola Tesla in 1891. The tesla coil is used to produce high voltage, low current,and high frequency alternating electricity. Tesla coils are a source of Artificial Plasmas. Tesla coils are commonly seen in many modern day entertainment such as television, as well as in plasma globes. Within a plasma globe, is an electrode, that uses the inert gasses that make up plasma. The wires within the globe transfer energy, giving the purple fluorescent light effect.