قانون أوم - الطاقة الكيميائية .. الفيزياء

Ohm's Law - Chemical Energy .. Physics

Ohm's Law

There is a great similarity between the passage of electric current in a metal wire and the flow of water in a pipe, if we consider that the amount of water flowing in one second is similar to the number of electrons passing in one second as well, i.e. the electric current itself. If we continue the comparison, we find that the pressure required to maintain the water flow is similar to the electromotive force or voltage, and just as there is friction between the walls of the pipe and the water flowing in it, there is a type of resistance that impedes the passage of electricity in the body that carries it, and it results from the collision of atoms with the flowing electrons, which causes them to lose some of the energy they carry. The ohm is the unit of measurement of electrical resistance, which is the resistance of a wire through which one ampere passes and the potential difference between its two ends is one volt. In general, the resistance is equal to the product of the potential difference G divided by the current "according to Ohm's law G = Y M, by which all the properties of electrical circuits are known.

The electric lamp consists of a thin, very short, high-resistance wire (the lamp filament) located inside a swollen bottle that resembles an onion and is filled with one of the inert gases such as argon, for example. The resistance of the lamp and its power consumption are known based on the quantities of voltage and current passing through it (see the drawing).

When electrons flow inside a metal wire, the collisions between them and its atoms cause an increase in the force of their vibrations, which results in an increase in the temperature of the wire and in the average energy of its atoms alike. For this reason, the lamp filament glows with white light. The energy dissipated by the current (measured in joules) is equal to the product of the voltage by the electric current and the time N during which the current flows according to the following equation Q = J Y N which becomes if we use Ohm's law Q = Y2 M N.

(On the left) The light bulb is lit by a 220 volt supply and consumes a current of 0.45 amperes, so its resistance becomes 220/0.45 = 490 ohms and its power consumption is 0.45 × 220 = 100 watts.

(On the opposite page) The passage of current resulting from a difference in potential is similar to the flow of water resulting from high pressure.

It is known that the capacity of an energy source is the rate of its ability to produce work, and it is measured by a unit called watt, which is a joule per second. The equation on the basis of which the capacity of an electrical device is calculated is J or Y m.

The unit used to pay electricity costs is the kilowatt-hour, which is equal to 1000 × 3600 watt-second, or 3.6 × 610 joules.

It is worth noting that the resistance of the conductor increases with the increase in its temperature and the number of collisions of its atoms with the electrons flowing in it increases as the vibrations of these atoms become stronger. In contrast, the resistance of the conductor decreases as its temperature decreases and becomes almost non-existent when it approaches absolute zero. Then, the vibrations of the atoms become so weak that the number of their collisions becomes negligible, and in such a case the conductor is called a superior conductor.