Resistor and Resistance : How to read resistor color code? Resistance is a property of conductor. Resistivity depends upon conductor to conductor. Some have less resistivity which is good conductor, some have high resistivity which is bad conductor. In a circuit the wire we use is good conductor and it has low resistivity. There is no material without resistance in the world. Every material has resistance. To create potential difference on a circuit the conductor is used called resistor. Resistor is the name of the element and resistance is the property of that element.
Figure: Practical resistors
Symbol of resistor
Generally resistor is defined with two symbols as below
Figure: Resistor circuit diagram or symbol
There are two symbols also depending on the value of resistor viz i) fixed value resistor and ii) variable resistor.
How resistors are made?
Resistors are named according to its construction. Generally we use carbon film resistor and carbon composition resistor in the circuit.
Carbon composition resistor is made of carbon compound with soil and resin mixture. In a thin conductor the total mixture is fixed with pressure from four sides. Resistor’s resistance value depends on carbon quantity in the mixture. Durability of this type resistor is very low. But tolerance or accuracy of the resistor is ±10%. It is cheap of cost. So it is used largely in general purpose.
In 1000◦C a ceramic rod is placed within methane vapor. Gradually methane oxidized on ceramic rod and a thin coating is filmed on the rod. This way carbon film resistor is made. Film resistance depends upon its thickness. The resistance of the resistor can be increased making spiral groove on its body. Durability of this type resistor is more. Tolerance of carbon film resistor is ±2%.
How to read resistor color code?
Battery, capacitor etc circuit element value is written down on its body. We can easily understand the value of them by observing its body. But resistors are very tiny element. The value of resistance of resistor cannot be written down on its body because it is so tiny and thick. How do people know the value of resistor? So that the scientists made a method to determine value of the resistor.
On the surface of the resistors some color band is marked. Each color has its individual value. There is a formula to find the resistor value. With the help of the formula and color code value resistor value can be specified easily. The color code is internationally accepted worldwide. The manufacturer of resistor follows the standard color code and resistors of different values are made by arranging band of different colors. No instruments needed to measure resistance value. In the following table code numbers of different colors, multipliers and tolerance are mentioned. Tolerance gives the value increase or decrease from exact value of resistance according to temperature.
Figure: 4 band color code chart of resistor
From the rules of color code the value of resistance = FS × 10T ± Tolerance
Here,
F = First color value
S = Second color value
T = Third color value
And there is a fourth band which represents tolerance.
Calculation method
Manufacturer made 4 band resistor and 5 band resistor. Now we have to see how to find 4 band resistor value.
There is technique to memorize 4 band color code of resistance and that is memorize the sentence
B.B. ROY Good Boy Very Good Worker.
Follow the capital letter of the sentence. First B = Black(0), Second B = Brown(1), Third R = Red(2), Fourth O = Orange(3), Fifth Y = Yellow(4), Sixth G = Green(5), Seventh B = Blue(6), Eight V = Violet(7), Ninth G = Gray(8), Tenth W = White(9).
In this process it is easy to memorize.
4 band color resistor
Suppose, A carbon resistor surface is marked with brown, yellow, red and gold color. Find the maximum and minimum value of the resistor.
Answer: One common question is which one is 1st band color? We can take 1st band from left or right. There is solution that place gold or silver color at right side and count from left 1st band. Gold and silver color basically marked for tolerance. Some resistor has no 4th band color. In this situation we will count color code from the side which is near resistor terminal point.
However, from the given information
First color code is brown, F = 1
Second color code yellow, S = 4
Third color code for multiplier, T = 2
Tolerance for gold color = ±5%
The resistance of the resistor = FS × 10T ± tolerance
= 14 × 102 ±5%
=1400 ±5%
5% of 1400 is 70. So for getting maximum value add and minimum value subtract.
Maximum value of resistance = 1400 + 70 = 1470Ω
Minimum value of resistance = 1400-70 = 1330Ω
In this way we can find out 4 band resistor value.
Practical resistor value find out
Figure: 4 band practical resistor
In above image there is a 4 band resistor which color code band are following
First color code is brown, F = 1
Second color code is black, S = 0
Third color orange for multiplier, T = 3
Tolerance for gold color = ±5%
The resistance of the resistor = FS × 10T ± tolerance
= 10 × 103 ±5%
=10000 ±5%
5% of 10000 is 500
Maximum value of resistance = 10000 + 500 = 10500Ω
Minimum value of resistance = 10000-500 = 9500Ω
The resistor value is 10000Ω or 10kΩ.
If the value increases it will be maximum 10500Ω
And if the value decreases it will be minimum 9500Ω.
Figure: Resistor value measurement from multimeter in Ohm
See we measure the resistor value with multimeter which is in kΩ. So our calculation is collect.
5 band color resistor
For 5 band color resistor the following table code
Figure: 5 band resistor color code
Calculation
A 5 band color resistor is shown in figure.
It has five colors green, black, black, red and silver.
The first three colors is for first three digit. Fourth color is for multiplier and fifth is tolerance.
The formula is = FST × multiplier ± tolerance
= 500 ×100 ± 10%
= 50000 ± 10%
10% of 50000 is 5000
The resistor value = 50kΩ or 50000Ω
The maximum value = 50000 + 5000 = 55000Ω
The minimum value = 50000 – 5000 = 45000Ω
