When an external power source is applied, the resistor produces a voltage across its terminals that is proportional to the electric current passing through it in accordance with Ohm's Law:V = IR
A Resistor is the most basic and common electronic Component. A resistor is used to resist electrical Current (not voltage), and is measured in Ohms, where one ohm is the amount of resistance that one Volt can push one Amp through. 5v could push 1A through 5 ohms of resistance, .5A through 10 ohm of resistance, or 5A through 1 ohm of resistance.
Resistors come in varying values, and Watt ratings.
Resistors in series
Resistors inline with each other act as a single resistor where resistance is the total sum of all of their values. So you simply add them all up. 1ohm + 3ohm + 4ohm = 8ohm.
Resistors in parallel
Resistors in parallel are quite different where the effective resistance is always less than the lowest ohm resistor. One over the total resistance (1/T) = (1/R1) + (1/R2) +(1/R3) and so on.
The easiest is if 2 resistors are in parallel, and each have the same value, the total resistance, is just half. So 2 8ohm resistors in parallel is 4 ohms.
Reading a resistor
Through-hole resistors are colour coded so that you can easily read the resistance. Bands of colours show different numbers. The numbers 0 to 9 are represented by colours in the order "Black Brown Red Orange Yellow Green Blue Violet Grey White"
There is also a band on the end that shows the tolerance, the colours Brown to Yellow represent 1% to 4% tolerance, gold represents 5% and silver 10%.
To read the value from a four-colour-band resistor you first make a number from the first and second colour bands, for example if you had a green, blue, brown(, gold) resistor then you take the the green and blue and get 56 (green represents 5 and blue represents 6).
Once you have that you get the exponent from the third band, in this example it is brown, this represents 1, so the value of the resistor in ohms is 56E1 OR 56*10^1 OR 56*10 = 560 Ohms (±5% for the gold tolerance band).
Five band resistors are the same but with three numbers before the exponent, so a Brown, Black, Black, Red(, Brown) resistor is 100E2 OR 100*10^2 OR 100*100 = 10,000 Ohms, this is often shortened to 10K Ohms (±1%)
Sometimes a mnemonic device is used to remember the order. An example of one is:
"Bad Beer Rots Our Young Guys, But Vodka Goes Well".
Colour charts are used to make reading resistors simple.
This colour chart shows you how to read the resistance of a resistor
Colour codes for reading resistance of a resistor
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