Skip to main content

SOURCES OF ELECTRICITY

The five most important sources of electricity for technicians are chemical action, heat, light, pressure, and magnetism.

1) CHEMICAL ACTION

In the electrical and electronics fields, battery is the backup source of electricity. Batteries produce electrical energy by a chemical action.

2) HEAT

Heat can be used to free electrons from some metals and from specially prepared surfaces. When some materials are heated to a high temperature, electrons are freed from their surfaces. Any nearby metallic surface, if positively charged, attracts these electrons and produces electron flow. The freeing of electrons by heat is called thermal emission.

3) LIGHT

Light striking the surface of certain materials can be used to free electrons. This is called photoemission. With a suitable collecting surface, useful electron flow can result. Photoemission is used in photoelectric devices and television camera tubes.

4) PRESSURE

Mechanical pressure on certain crystals can be used to produce electricity. The crystal cartridge of an inexpensive record player is a good example. The needle causes a changing pressure. The crystal produces a changing voltage in step with the grooves in the record.

5) MAGNETISM

The most common method of generating electrical power is by turning a coil of wire in a magnetic field. This is the method the power station uses to generate the electric power that is used in homes, business, and industry.

Comments

Post a Comment

Popular posts from this blog

ADVANTAGES AND DISADVANTAGES OF CORONA

Corona has many advantages and disadvantages. In the correct design of a high voltage overhead line, a balance should be struck between the advantages and disadvantages. ADVANTAGES (i) Due to corona formation, the air surrounding the conductor becomes conducting and hence virtual diameter of the conductor is increased. The increased diameter reduces the electrostatic stresses between the conductors. (ii) Corona reduces the effects of transients produced by surges. DIS-ADVANTAGES (i) Corona is accompanied by a loss of energy. This affects the transmission efficiency of the line. (ii) Ozone is produced by corona and may cause corrosion of the conductor due to chemical action. (iii) The current drawn by the line due to corona is non-sinusoidal and hence non-sinusoidal voltage drop occurs in the line. This may cause inductive interference with neighboring communication lines.
Read more

ADVANTAGES OF PER UNIT SYSTEM

PER UNIT SYSTEM The per-unit system expressed the voltages, currents, powers, impedances, and other electrical quantities basis by the equation: Quantity per unit (pu) = Actual value/ Base value of quantity ADVANTAGES OF PER UNIT SYSTEM While performing calculations, referring quantities from one side of the transformer to the other side serious errors may be committed. This can be avoided by using per unit system. Voltages, currents and impedances expressed in per unit do not change when they are referred from one side of transformer to the other side. This is a great advantage. Per unit impedances of electrical equipment of similar type usually lie within a narrow range, when the equipment ratings are used as base values. Transformer connections do not affect the per unit values. Manufacturers usually specify the impedances of machines and transformers in per unit or percent of name plate ratings. Transformers can be replaced by their equivalent series impedances. ...
1 comment
Read more

ABSOLUTE AND SECONDARY INSTRUMENTS

The various electrical instruments may, in a very broad sense, be divided into (i) Absolute Instruments (ii) Secondary Instruments. Absolute Instruments are those which give the value of the quantity to be measured, in terms of the constants of the instrument and their deflection only. No previous calibration or comparison is necessary in their case. The example of such an instrument is tangent galvanometer, which gives the value of current, in terms of the tangent of deflection produced by the current, the radius and number of turns of wire used and the horizontal component of earth’s field.  Secondary Instruments  are those, in which the value of electrical quantity to be measured can be determined from the deflection of the instruments, only when they have been pre-calibrated by comparison with an absolute instrument. Without calibration, the deflection of such instruments is meaningless. It is the secondary instruments, which are most generally used in ev...
Post a Comment
Read more