What is a resistor?
are made from carbon and clay mixtures,they are cheap and easily available and also it is the most common type found in all circuits boards.
as shown in the figure above common resistors have color strips on them which can be 4,5,6 different colors called bands.
as shown above,band A is brown=0, band B=red=2,band c=brown=0,band d= gold =5%.
A resistor can simply be defined as an electronic material that offers the resistance to flow of current in a circuit. Resistors are used for limiting excess current or voltage in a circuit.They are often used in AC and DC circuits.
circuit symbol of a resistor.
Types Of Resistors Used In Circuits.
1.carbon capacitors.
They are available in wide range values ranging from 1 ohms to 22M ohms and they are usually used in Arduino boards.
2.variable resistor.
This type of resistors resistance can be varied by turning their shafts,they are used in radio tunning circuits,volume tunning and so on.
Symbol of a Variable resistor
3.LDR (light dependent resistor).
Their resistance depends on light,their resistance decreases
When left light falls on them and also increases when placed in dark spots.
They are used in making streets lights and equipments which are made to work in daylight.
LDR are made from calcium sulphide a (semiconductor material which has little electrons when placed in dark but conducts smoothly when photons or light waves impinge on it.
LDR circuit symbol.
4.thermistors.
They are also known as thermal resistor,their resistance depends on the temperature around them and as well as the temperature they absorb from their surroundings.
We have two types of thermistors namely;
(a) NTC (negative type coefficient)-
their resistance reduces or drops to zero when their temperature is raised. They are used in fire alarm systems, automatic air conditioner etc.
(b) PTC (positive type coefficient)-
their resistance increases with increase in temperature,they are use in controlling smart phones from over heating, controlling heating systems etc.
5.Wire coil resistors.
they are also known as wire wound resistors,they are made from constatan wire and manganin and wound on an insulated pipe as the base, they are usually used in electrical physics practicals and also for producing vairable resistance in a circuit. It consists of a slider that is used to change the coil's length which in turn changes it resistance according to the length.
it works on this formular;
R=el/A
hence e= resistivity constant of the coil,
R= resistance of the coil,
L=length of the coil,
A= cross sectional area of the coil.
6.Varistor.
thesee are non linear resistors,they are non ohmic conductor i.e they don't obey ohms law( states that the current (I) passing through a metalic conductor is directly proportional to applied voltage(V) accross it ends provided that temperature and all other physical properties of the conductor are kept constant. Thus V is directly proportional to I,when R is constant hence V=IR ,note; R= resistance.
They are made with semiconductors like sillicon Carbide and zinc oxide.
There are three types of varistors namely Sillicon carbide disc type,Sillicon carbide rod type and Zinc oxide type.
7.Metal film resistors.
they are made by coating or depositing of conductive materials like carbon or metals on an insulated base,their resistance value can be made up to 10,000M ohms.
Prefix used in resistors value.
Resistance of a resistor is measured in ohms named after Goerge ohms(Ω).
We use prefix to shorten the amount of zeros we place at the back of high resistance values,here are the lists:
1. KΩ= kilo ohms = 1000Ω.e.g 200kΩ
2.MΩ= mega ohms= 1000000Ω
Etc.
How to Calculate resistance value of a resistor.
So my dear readers you need to know color and their codes.
Resistors color codes.
Colors. codes.
Black 0
Brown 1
Red 2
Orange. 3
Yellow. 4
Green. 5
Blue 6
Violet. 7
Grey 8
White. 9
I guess you were confused on how to memorize it 😁,lol i will help you,just memorize this my funny peom. And match to the one above.
Big
Boys
Race
Our
Young
Girls
But
Violent girls
Generally
Wins.
Tolerance values
Tolerance means the percentage measure of the accuracy of a resistor from its preferred value.
Colours and their tolerance values.
Gold=5%
Silver=10%
calculating resistance value of a resistor.
formula=first band,second band then multiplied by 10 raised to power of third band.
So resistance value=1,2{we write both bands values together as shown in the answer}×10^1
=120 ohms.
To calculate the tolerance value. 120×5%=6,
Tolerance value =120+or- 6=126 or 114 ohms.thus the resistance if the resistor above ranges from 114 to 126 ohms
example;
let's calculate this resistor resistance value.
Calaculation
1st band - brown= 1
2nd band- black = 0
3rd band- red =2
4th band- gold 5%
formula=first band,second band then multiplied by 10 raised to power of third band.
Thus resistance=,1,0×10^2
= 1000ohms= 1k ohms.
So tolerance value;
=1000×5%=50
=1000+or- 50
=950 to1050Ω.
Calculating resistance values of resistors connected together.
There are basically two ways to connect resistors in circuits namely;
(a)Series connection;
when they are connected one after each other it is called series connection, to calculate we use the formular, r1+r2+r3+ r4+.............e.t.c
(b)parralel connection;
they are connected end to end and are calculated as follows,1/r1+1/r2+1/r3+1/r4+............etc.
I hope you understand our tutorials if you have any question please feel free to comment on this post.
