Resistor

CHAPTER 2

https://goo.gl/0H6QQG

RESISTOR

I.                    Definition

From the root word itself which is “resist” it means “to go against” or “to oppose”. In the early part of this book is the history of electricity. Upon the discovery of it, people before wanted to make use of it that pushed them to conduct further studies how to maximize and use it effectively. It was then the discovery of Georg Simon Ohm that every conductor tends to oppose to the flow of charges named as resistance. This was the idea of making resistor which is used to control the flow of charges or the current itself. Resistors are also named as “Passive Devices” since they don’t contain source of power but they can only reduce the flow of charges to come up with the desired current in a certain circuit.

II.                  Types

Resistors come in many forms, sizes and colors but they all serve the same purpose. There are actually two types of resistor, the Fixed and the Variable resistor. For the fixed resistors, these are what we commonly see which have fixed value of resistance. For the variable resistors, we have the potentiometer and rheostat as examples in which the resistance can be adjusted whenever we want.

The making of a resistor is not that merely making one since its composition would also tell the value of its resistance. Not all conductors have the same resistance that is why we have many values for the resistance. It is not also made to have fixed value of resistance since it will depend to our desired current. I will name some composition types of resistor. These are:

a.       Carbon Resistor – is the most common type of resistor. It is cheap and has general purpose used in electrical circuits. From the name itself it will be obvious that it is made of finely carbon dust or graphite paste and a ceramic clay powder which is non-conductive to mix them all. This composition is considered to have low wattage values. The ratio of the conductor to the insulator will tell us it overall resistance value. Meaning the higher the ratio of carbon the lower the resistance.

http://goo.gl/aa7cEz

https://goo.gl/U4WwzM

a.       Film Resistor- under this type are Metal Film, Carbon Film and Metal Oxide Film resistor types which are using pure metals as its composition like nickel. It resistance value will be based on the thickness of the deposited film. The thicker the film, the higher the resistance.

https://goo.gl/wFdGrX

https://goo.gl/7CRLPH

a.       Wire-wound resistor – its composition is wire usually made of alloy like Nichrome. It is considered to have very low resistance but can greatly affect power.

http://goo.gl/GIsW5

I.                    Color coding

Without testing the resistance of any resistor, we could identify it through the color codes imprinted in its body. Each color corresponds to a number. For a four banded resistor, the first two colors represent the first digits of the value, the third color will be the multiplier and the fourth will be the tolerance. The table below shows the numbers designated for the colors.

COLOR	DIGIT	MULTIPLIER	TOLERANCE
Silver		x 0.01	±10%
Gold		x 0.1	±5%
Black	0	x 1
Brown	1	x 10	±1%
Red	2	x 100	±2%
Orange	3	x 1 k
Yellow	4	x 10 k
Green	5	x 100 k	±0.5%
Blue	6	x 1 M	±0.25%
Violet	7	x 10 M	±0.1%
Grey	8	x 100 M
White	9	x 1 G

Here are some examples on how to read the resistance using the color coding.

But to have exact values of the resistance, we can use the ohmmeter which is a device designed for measuring current because color coding is not exact knowing that it has tolerance.

IV. Types of resistor connection

a. Series connection - is a connection in which the resistors are connected in series with each other. With this type of connection, there is the same amount of current passing through each other. Thus in calculating for the equivalent resistance, it is just the summation of all the resistors. Below is an example of resistors in series.

So if you will try to calculate the equivalent resistance, then it will simply be R_eq=R₁ + R₂ + R₃

b. Parallel connection – is a connection in which the resistors are connected in parallel with each other. This time, the current will not be the same all throughout the circuit because of junctions. Here is an example of parallel connection.       

  

So if you will try to calculate for the equivalent resistance, it will be 1/R_eq = 1/R₁ + 1/R₂ +1/R₃ +1/R₄

c. Series-Parallel/Network/Combination Connection – it is the combination of series and parallel. Meaning in one circuit, we can see a series and a parallel connections making it to be called Combination also. Below is the example of Network connection.

By this time, the R_eq will be the combined R_eq of the series and parallel. You just have to solve it circuit by circuit. 

As a whole, resistor plays a vital role in the world of electricity. Without it, there will be no gadgets and other inventions today since the production of electricity is not enough knowing that if it is not controlled, it can cause destruction and tragedy. It is very essential role in electronics is to control the current to come up the desired one. It serves as protector with the different circuit elements or the device itself from destruction brought by huge amount of current.

The importance of resistor may not be appreciated well but for me it plays a very essential one and I am amaze with the persons behind this idea of making a current regulator.

V.                    Sample Laboratory Experiment

a. Series Connection: V_out= 7.8v

Resistance	Resistance Coding	Colors	Vdrop Theoritical	Vdrop Experimental	Current Theoritical	Current Experimental
R1= 5500 Ω	5600 Ω	G, B, R, Gold	1.9085 V	1.8 V	3.47×10-4 A	3.25 ×10-4 A
R2=350 Ω	350 Ω	O, W, Br, Gold	0.12145 V	0.12 V	3.47×10-4 A	3.25×10-4 A
R3=1000 Ω	1000 Ω	Br, Bl, R, Gray	0.347 V	0.31 V	3.47×10-4 A	3.25×10-4 A
R4=3400 Ω	3300Ω	O, O, R, Gold	1.1798 V	1 V	3.47×10-4 A	3.25×10-4 A
R5=4700 Ω	4700 Ω	Y, R, V, Gold	1.6309 V	1.4V	3.47×10-4 A	3.25×10-4 A
R6=7500 Ω	7500 Ω	V, Gr, Re, Gold	2.6025 V	2.3 V	3.47×10-4 A	3.47×10-4 A
Total: 22450			7.8 V	6.93 V	3.47×10-4 A	3.47×10-4 A

Voltage

%diff= theo-expe×100%= 7.8 V – 6.93 V ×100%= 11.15%

                   Theo                           7.8 V

Current

%diff= theo-expe×100%=3.47x10^-4A – 3.25x10^-4A×100%= 6.34%

                   Theo                           3.47x10^-4A

b. Parallel Connection V_out= 5.4 V

Resistance	Resistance Coding	Colors	Vdrop Theoritical	Vdrop Experimental	Current Theoritical	Current Experimental
R1= 5500 Ω	5600 Ω	G, B, R, Gold	5.4 V	5.4 V	9.8×10-4 A	9 ×10-4 A
R2= 350 Ω	350 Ω	O, W, Br, Gold	5.4 V	5.4 V	0.0159 A	0.0137 A
R3= 1000 Ω	1000 Ω	Br, Bl, R, Gray	5.4 V	5.4 V	5.4×10-3 A	5.5×10-3 A
R4= 3400 Ω	3300Ω	O, O, R, Gold	5.4 V	5.4 V	1.588×10-3 A	1.7×10-3 A
R5= 4700 Ω	4700 Ω	Y, R, V, Gold	5.4 V	5.4 V	1.149×10-3 A	1.2×10-3A
R6= 7500 Ω	7500 Ω	V, Gr, Re, Gold	5.4 V	5.4 V	2.2×10-3 A	1.2×10-3 A
Total: 22450			5.4 V	5.4 V	0.025A	7.3×10-4 A

R_T=231.71Ω                                            

Voltage

%diff= theo-expe×100%= 5.4 V – 5.4 V ×100%= 0%

                   Theo                           5.4 V

Current

%diff= theo-expe×100%=0.025A – 0.024×100%= 4%

                   Theo                           0.025A

c. Network Connection V_out= 5.8 V

Resistance	Resistance Coding	Colors	Vdrop Theoritical	Vdrop Experimental	Current Theoritical
R1= 5500 Ω	5600 Ω	G, B, R, Gold	0.25 V	0.0225 V	4.5×10-5 A
R2= 350 Ω	350 Ω	O, W, Br, Gold	0.25 V	0.25 V	7.143×10-4 A
R3= 1000 Ω	1000 Ω	Br, Bl, R, Gray	0.76 V	0.74 V	7.61×10-4 A
R4= 3400 Ω	3300Ω	O, O, R, Gold	2.59 V	2.4 V	7.61×10-4 A
R5= 4700 Ω	4700 Ω	Y, R, V, Gold	2.20 V	2.11 V	7.61×10-4 A
R6= 7500 Ω	7500 Ω	V, Gr, Re, Gold	2.20 V	2.11 V	7.61×10-4 A
Total: 22450			5.8 V	5.49 V

% diff= (7.61 x 10^-4A - 7.20 x 10^-4A)/ 7.61 x 10^-4A x 100% = 5.39 %

References:

Retrieved on August 14, 2015 from http://www.electronics-tutorials.ws/resistor/res_1.html 

Retrieved on August 14, 2015 from https://learn.sparkfun.com/tutorials/resistors