The most common type is the 1/4W 5%carbon film resistor. To read the value, see the chart above.
Resistors are the most commonly used component in electronics and their purpose is to create specified values of current and voltage in a circuit.
The unit for measuring resistance is the OHM. (the Greek letter Ω – called Omega). Higher resistance values are represented by “k” (kilo-ohms) and M (meg ohms). For example, 120 000 Ω is represented as 120k, while 1 200 000 Ω is represented as 1M2. The dot is generally omitted as it can easily be lost in the printing process. In some circuit diagrams, a value such as 8 or 120 represents a resistance in ohms. Another common practice is to use the letter E for resistance in ohms. The letter R can also be used. For example, 120E (120R) stands for 120 Ω, 1E2 stands for 1R2 etc.
Here is a quick explanation on how to calculate the value of a resistor according to the colors of its bands.
e.g. A resistor with the colours YELLOW, VIOLET, BROWN, GOLD.
First band is YELLOW, which you can read as a value of 4
Second band is VIOLET, which you can read as a value of 7
Third band is BROWN, this indicates a multiply x10
Now put these figures together and you will have the follow:
4 7 x10 = 470Ω, (Ω is the symbol used for ohms, the measure of resistance).
Fourth band is GOLD, which will give you a tolerance of 5%
That said, let’s imagine that we want to calculate the resistor needed to go alongside an led diode.
For example, given a 9-volt battery, and a 2-volt LED with a maximum current of 30 ma, the required resistance R is (9 V — 2 V)/0.03 A = 233 ohms. Note that milliamps must be converted to amps by dividing by 1000. Also, the absolute minimum R should be avoided, it is preferable to use a 240-ohm, 330-ohm or higher valued resistor instead.
That’s it for today, this was part 1 of the Basic components, on part 2 we will talk of capacitors.
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