What is Resistance? Color Codes and Calculation

In this article, we will cover topics such as what resistance is, color codes, and resistance calculations, providing you with information on selecting the appropriate resistance for your project and determining the ohm value of a resistance when you don't know its value. Here are the topics we will discuss:

 

Resistance is a circuit component used to reduce voltage and share voltage in a circuit. It is represented by the symbol R and measured in Ohms (Ω). For example, if we want to light a 3V LED with a 9V power source, we need a resistor that will reduce the voltage to 6V. Resistors maintain voltage in the circuit, leading to energy loss and generating heat as a result. We'll discuss resistor selection and how to determine the required ohms and wattage shortly.

 

Ohm's Law is one of the fundamental laws of electricity, expressed as V=IxR, where V is voltage, I is current (in Amperes), and R is resistance (in Ohms). It was discovered by the German physicist George Simon Ohm in 1827, hence the name Ohm and the unit Ohm.

 

Calculating the required resistance in circuits can be a challenge for those unfamiliar with the process, but it's relatively straightforward. Let's consider lighting a LED again.

 

The formula for resistance calculation is:

Resistance (R) = (Supply voltage - LED voltage) / LED current.

If our supply voltage is 12V, the LED voltage is 3V, and the current is 0.20A, what ohm value resistor should we use? Applying the formula:

Resistance = (12-3) / 0.02 = 9 / 0.02 = 450 Ohms.

 

The wattage of the resistor is calculated as W = Voltage across the resistor x Current. So, 9 x 0.02 = 0.18 watts. Therefore, we can use a 0.25 or 0.50 watt resistor.

 

The resistance color codes are as follows:

 

Resistance is calculated using the table above. The formula for resistance calculation is: The first and second color bands are written side by side and multiplied by the coefficient of the third color band. The fourth color band represents the tolerance value as a percentage.

 

For example, in the image, there is a 10K or 10,000 Ohm resistor. Let's calculate it:

 

The first band is brown, which corresponds to the number 1. The second band is black, representing 0.

The third band is orange, which corresponds to the coefficient of 103.

When we put the numbers obtained from the first two bands side by side and multiply them by the coefficient, we get 10 x 103 = 10,000 ohms. The fourth band is gold, indicating a tolerance of 5%. Therefore, the actual value of this resistor is between 9500 - 10500 ohms.

 

There are many types of resistors, including fixed-value resistors, adjustable resistors, and resistors that vary according to environmental conditions. Carbon resistors and SMD resistors are fixed-value resistors commonly used in our circuits. Potentiometers have adjustable resistance. PTC and NTC resistors vary with temperature, while LDR varies with light intensity.

 

Parallel resistors are connected as shown in the circuit diagram below.

 

Parallel resistors are calculated using the formula below:

 

Series resistors are connected in sequence in the circuit. They are calculated using the following formula: