WHAT IS ELECTRICAL RESISTANCE
Electric resistance is any opposition that current encounters as it passes through a closed electrical circuit, attenuating or slowing down the free flow of circulation of electrical charges or electrons. Any device or consumer connected to an electrical circuit represents in itself a load, resistance or obstacle for the circulation of the electric current.
Normally the electrons try to circulate through the electrical circuit in a more or less organized way, according to the resistance they encounter. The lower this resistance, the greater the order existing in the micro world of the electrons; but when the resistance is high, they start to collide with each other and release energy in the form of heat. This situation causes the conductor temperature to always rise somewhat and, in addition, it acquires higher values at the point where the electrons find a greater resistance in their path.
Resistance of metals which allow the current to pass through them
All known materials and elements offer greater or less resistance to the passage of electric current, including the best conductors. The metals that offer the least resistance are gold and silver, but due to the costly cost of making cables with these metals, it was adopted to use copper, which is a good conductor and much cheaper.
With copper wire most of the conductive cables that are used in low and medium voltage circuits are manufactured. Aluminum is also used on a smaller scale to manufacture the cables that we see placed in the high-voltage towers to transport electrical energy over great distances.
A.- Variable resistance or rheostat made with nichrome wire (Ni-Cr). .
B.- Carbon potentiometer, widely used in electronic equipment for . control, for example, the volume or tones in the audio amplifiers. This potentiometer in the figure is controlled by rotating its axis towards . right or left, but there are others with a lever . slider to achieve the same end.
C.- Fixed carbon resistance, widely used in electronic circuits.
Among the metals that offer greater resistance to the passage of electric current is the nichrome wire (Ni-Cr), made up of an alloy of 80% nickel (Ni) and 20% chromium (Cr). This is a type of wire widely used as a fixed resistance or as a variable resistance (rheostat), to regulate the voltage or voltage in different electrical devices. In addition, fixed resistors of nichrome wire of different diameters or thicknesses are also used to produce heat in industrial equipment, as well as in widely used household appliances.
Among those devices or equipment are irons, electric heaters or stoves used to heat the room environment in winter, water heaters, clothes dryers, hair dryers and most electrical appliances whose function main is to generate heat.
Another element widely used to make resistors is carbon. With this element, fixed resistors and rheostats are manufactured for use in electronic circuits. Both the fixed resistors and the potentiometers are used to regulate the values of current or voltage in electronic circuits, such as, for example, low-frequency or audio-frequency currents, allowing, among other things, to control the volume and tone in the audio amplifiers.
Also Read: What is Conductance and Conductivity
What is Ohm
The ohm is the unit of measure of the resistance that materials oppose to the passage of electric current and is represented by the Greek symbol or letter ” Ω” (omega). The reason why it was agreed to use that Greek letter instead of the “O” in the Latin alphabet was to avoid it being confused with the number zero “0” .
The ohm is defined as the resistance offered by the passage of electric current a 106.3 cm high column of mercury (Hg), with a cross section of 1 mm 2 , at a temperature of 0 o Celsius.
According to the “Ohm’s Law”, an ohm (1 Ω )is the value which has an electrical resistance when the electric circuit connected to a one volt (1 V) of voltage causes a current flow of one ampere (1A) . The general formula of Ohm’s Law is as follows:
The electrical resistance, on the other hand, is identified with the symbol or letter (R) and the formula to clear its value, derived from the general formula of Ohm’s Law, is as follows:
Types of Resistors
Depending on its operation we have:
Fixed resistors : They are those that have a value that we cannot modify.
Special resistances : They are the ones that vary their value depending on the stimulation they receive from an external factor (light, temperature …). For example, LDRs are those that vary their value depending on the light that falls on them.