Before explaining resistor functionality to you, let me explain functionality of a resistor with something other than electricity. I would first show you an image.
In the above image, you can see a water filled tank with a water pipe. While the tank is filled, water can easily flow through the attached pipe to the exit and flows out freely. The water drains in large amount but what if you need smaller amount of water instead? What will you do? In the same image you can see another similar water tank filled with water with similar pipe attached to it with only difference that a pipe of smaller diameter is attached within this pipe as a resistance. You can see the amount of water draining from this pipe is much lower than the other tank? Why is it so? After taking a look at this image, you can easily say that the pipe with smaller diameter attached in between the big pipe is not letting enough water to flow. Due to shorter diameter of attached pipe, less water is flowing resulting in less water output. That is easy to understand, isn’t it?
Well now let’s look at the other side of the same image; you can see two bulbs, one in upper portion and one in lower portion. The bulb in upper portion is glowing brighter while the bulb in lower portion is providing less light. Why is it so? OK use your previous experience with water tanks, if you take a close look at the image, you will see a resistance attached in between the circuit of the less bright bulb. That resistance is allowing less electric current to flow towards the electric bulb causing the bulb to glow less than the other bulb which is directly attached to the current source without any resistor.
Now to summarize what we have learned, in this image the functionality of the pipe with shorter diameter and functionality of electric resistor is same. The pipe with shorter diameter allows less water to flow similarly the resistor used in the way of electric bulb allows less current to flow towards the bulb. Alright so until now we have learned that a resistor is a small component commonly used in electronic circuits to limit or reduce amount of electrical current.
Now when you know what a resistor is and what is its use, I am pretty sure you would like to see how it looks like.
Types Of Resistors
If you have ever seen a circuit board then I am pretty sure you have already seen resistors in one form or another. Most common forms of resistors can be easily spotted by their color bands. I have attached an image containing some common types of resistors which will give you an idea of how they may look like.
Please note that there are hundreds of thousands of different looking resistors from different brands out there so the resistors shown in the above image may or may not be present in the circuit boards of your area but the chances are bright that there should be some resemblance.
Fixed And Variable Resistor Explained
The difference between fixed and variable resistors is almost self-explanatory. Fixed resistors have fixed amount of resistance which cannot be willingly changed. This resistance is calculated in Ohms. Say if a fixed resistor is rated at 220Ohm, It will always resist electricity by the same value. On the other hand, a Variable resistor can change its resistance between the zero Ohm and the maximum Ohm value written on it. Say if a variable resistor is rated at 220Ohm, its resistance value can be changed from 0Ohm to 220Ohm by rotating its nob or by taking whatever action is necessary to change its ohm value.
In this image you can see two water tanks, one has a fixed smaller diameter pipe attached in the way of its main water pipe which resists normal water flow and lets less amount of water to drain but this amount of water is fixed. We cannot increase or decrease the amount of resistance which this smaller diameter pipe applies to the outgoing water. On the other hand, the second water tank has a water valve attached in between its main water pipe. This valve can be used to change water flow by increasing and decreasing resistance in the way of water flow. The same thing can be applied to electric current. A fixed resistor has a fixed resistance which cannot be changed but a variable resistor can change its resistance just like a water valve. We can rotate a variable resistor to increase or decrease current flow just like a water valve can be rotated to increase or decrease water flow.
Many other types of resistors also exist like LDR (Light Dependent Resistor) which change their amount of resistance with respect to the amount of light they are facing. Thermistors are also actually a type of resistors which changes its resistance with respect to their temperature but my tutorial will only cover fixed and variable resistors for now. Alright, now you know what a resistor is, what are its common types and what is the difference between them. Next step is how to read resistor’s resistance value. It seems funny but resistor values are not always written exactly but instead most of the time, the value is encoded either in color code or in printed number code.
Resistors are normally small in size, so small that it is difficult to write their actual value on such small surface, even if it would have been written, it will be extremely difficult to read it from such small surface area. Therefore the resistance value of a resistor is normally written on it as color code displayed as color bands. The value is normally written as 4 band, 5 band or 6 band code. I have attached an image below showing color codes along with their values and calculation method of 4 band color coded resistors.
Resistor Color Code Band
In this image, you can see a resistor on top left having 4 color bands on it. The left three color bands are relatively closer to one another while the right color band at more distance. When we read a 4 band color resistor, we will start from the left side, the side with 3 close color bands. First two colors of a 4 band resistor are actually first two figures of our decoded figure and the 3rd color is decimal multiplier which we will multiply with first two figures to get the value of resistor. The last and the further most color represents the +- tolerance of the resistor. Say if a resistor’s value is 100 Ohm and its last color is golden which means +-5% then this resistor can have a value somewhere between 95 Ohms to 105 Ohms.
In the above image, the first color of the shown resistor is brown and the value of brown in the color chart is 1 so the first figure of our decoded figure is 1. The second color band is black and the value of black is 0 therefore our second decoded figure is 0. By combining first and second decoded figure we get 10. Now let’s look at the third decoded figure which is orange. By taking a look at the table, orange color as a multiplier has a value of 1000 so by multiplying 10 with 1000 we get the value 10,000 Ohm so we can say that the resistor shown in the above image is a 10000 Ohm or 10K Ohm resistor.
Variable resistors and some resistors show their values as printed code. For instance a 10K variable resistor may show its value written as 103. In this code, 10 or first two figures are taken as they are and the 3rd figure is taken as power of10 multiplier. So (103) =10 x 1000 = 10,000 or 10K Ohm.
Resistors in Parallel and Series
If we connect two resistors in series, their value will add up. For instance if we connect two 1K Ohm resistors in series, their total value will become 2K. If we connect three 1K resistors in series in a circuit, their value will be 3K. To put this into formula, R=R1+R2+R3 (R=1000+1000+1000=3000 Ohm or 3K Ohm)
On the other hand, if we resistors in parallel in a circuit, their value can be calculated using this formula, 1/R=1/R1+1/R2+1/R3…… Say we connect four 1000 Ohm (1K) resistors in parallel, their resistance value can be calculated using this formula like this. (1/R=1/1000+1/1000+1/1000+1/1000)=1/250. So their resistance value will be 250 Ohm when connected 4 of them in parallel.
To further explain it, I have attached an image as well. Please have a look.
12V Led Circuit Diagram
Now when you have read through my tutorial and have most basic information about resistors, it’s time to show you a very simple circuit diagram to explain resistor’s basic functionality. 12V power supply is one of the most common power supplies available. Most cars have 12V battery inside them so you can test this circuit using your car battery but any other 12V power source will work as well. This circuit is so simple that it only consists of an LED and a 1K resistor. In the following image, I have shown the circuit in both forms, in a circuit diagram form as well as in a photo form showing actual LED and actual 1K resistor connected together.
If you think this information was useful to you, please bookmark it on Facebook or any other social bookmarking websites you use so that other may also take benefit from this tutorial. Please feel free to ask questions in the comments section bellow.
Posted or Updated On:May 30, 2012