Resistors are devices that compose electric circuits several, its basic purpose is the conversion of electricity in Thermal energy (Joule Effect). Another function of resistors is the possibility of changing the potential difference in a certain part of the circuit, this is due to the decrease in the electric current due to the presence of the equipment.
Representation
The symbols below are used to represent resistors in an electrical circuit.
Where are they found?
Resistors are present in most equipment used in our daily lives, whether in electric showers with the function of providing heat to water, or in the composition of electronic circuits.
In the figure above, the small cylindrical devices, named by R followed by any value, R79 and R92 for example, are resistors.
Rheostats
You rheostats they are variable resistance resistors. Lamps that have variable brightness and volume buttons on stereos are examples of rheostat applications. In these equipments, the resistance of the resistor is changed in order to modify the value of the electric current, increasing or decreasing the brightness of a lamp and the volume of a stereo.
The symbol below represents rheostats in an electrical circuit.
color code
The resistors that make up electrical circuits usually have four colored bands, the function of colors is to determine the resistance value of the resistor without the need for measuring devices.
The first two color bands represent the first two digits of the resistance value. The third range indicates the number of zeros that make up the resistance value. The fourth range represents the tolerance or uncertainty of measuring the resistor value. Being gold, the uncertainty will be 5%, the silver shows that the resistor has 10% uncertainty. If the fourth range does not exist, the uncertainty in the resistor resistance value will be 20%.
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The table below indicates the value associated with each possible color of the bands of a resistor.
From the color code, the resistor resistance below can be determined.
1st color: Orange - First digit = 3
2nd color: Orange - Second digit = 3
3rd color: Brown - Number of zeros or base 10 power exponent value = 1
4th color: Gold - 5% tolerance
Resistance value: 330 ± 5% Ω. The resistance value can range from 313.5 Ω up to 346.5 Ω.
Resistor association
In an electrical circuit, resistors can be arranged in two different ways. The different ways of organizing the positions of the resistors are called associations, and allow obtaining different values of electrical resistance.
serial association: The resistors are placed next to each other. In this association, the equipment will have the same electrical current and different potential difference.
parallel association: The resistors are placed on top of each other. In this association, the equipment will have the same potential difference and different electrical current.
mixed association: It occurs when in the same circuit there are resistors associated in series and in parallel.
By Joab Silas
Graduated in Physics
Would you like to reference this text in a school or academic work? Look:
JUNIOR, Joab Silas da Silva. "What are resistors?"; Brazil School. Available in: https://brasilescola.uol.com.br/o-que-e/fisica/o-que-sao-resistores.htm. Accessed on June 27, 2021.
