ElectricIty

E lectricity is one of the basic forms of energy. Electri­cal activity takes place constantly everywhere in the universe. Electrical forces hold molecules together. The nervous systems of animals work by means of weak electric signals transmitted between neurons (nerve cells). Electricity is generated, transmitted, and converted into heat, light, motion, and other forms of energy through natural processes, as well as by devices built by people.

Electricity is associated with electric charge, a property of certain elementary particles such as negative electrons and positive protons, two of the basic particles that make up the atoms of all ordinary matter. Electric charges can be stationary, as in static electricity, or moving, as in an electric current.

The charges are free electrons (in metals) or ions (in liquids and gases). We can easily understand the nature of the electric current on the basis of electron theory. An atom is a complex particle in which tiny electrons move around a nucleus. In metals some of the electrons move freely among the atoms. There are free electrons. The electromotive force causes the electrons to move through the metal conductor.

There are two types of the electric current, namely, the direct current (d. c. for short) and alternating current (a. c.). The electric current can heat a conductor, it can have chemical action, or it can produce the magnetic effect.

Charges between clouds or between a cloud and the ground produce atmosphe­ric electrical discharges or light­ning. The flow of electri­city from one discharge point to another also produces a sound wave heard as thunder.

The electric current starts to flow from a battery or a generator, passes through wires, lamps, meters and other resistance and returns to its starting point. All these devices and conductors constitute the circuit. A steady electric current, like a water current, has the same value at all parts of a simple unbranched circuit.

The electric current flows only when there is a different of potential between the two points in the circuit. The opposition to the current flow is the resistance. Thus we can say that the current is directly proportional to the voltage and inversely proportional to the resistance (Ohm’s law).

There are special units of measurement of electric quantities. The ampere is a unit of rate of flow of electric current. The ampere indicates the amount of electric current. The volt is a unit of electrical pressure. The international volt creates a current of one international ampere in a conductor, which has a resistance of one international ohm. The watt is a unit of power, which electric devices develop. One watt is equal to a current of one ampere as a result of one volt.

We measure these electrical quantities with the help of special instruments named as measuring devices. We measure current with ammeter, voltage with voltmeter and power with wattmeter.

Ammeters measure the current flowing in a circuit and normally have scales graduated (or calibrated) in amperes, milliamperes, or microamperes. The ammeter has a low resistance coil not to absorb an appreciable amount of power; therefore, we connect the ammeter into a circuit in series.

Voltmeters measure the potential difference between the two points in a circuit. We connect a voltmeter in parallel across the points where it is necessary to measure the difference of potential. The resistance of voltmeter operation coil is as high as possible to limit the amount of power consumed by it.

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