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Cheat Sheet

Electronics For Dummies

From Electronics For Dummies, 2nd Edition by Cathleen Shamieh, Gordon McComb

Electronics is more than just schematics and circuits. By using various components, such as resistors and capacitors, electronics allows you to bend electric current to your will to create an infinite variety of gizmos and gadgets. In exploring electronics, it may be useful for you to have a handy reference for Ohm’s Law and Joule’s Law, for calculations, or for determining the values of resistors and capacitors according to the codes that appear on their casings.

Electronics Calculations Using Ohm’s Law and Joule’s Law

Ohm’s Law and Joule’s Law are commonly used in calculations dealing with electronic circuits. These laws are straightforward, but when you’re trying to solve for one variable or another, it is easy to get them confused. The following table presents some common calculations using Ohm’s Law and Joule’s Law. In these calculations,

  • V = voltage (in volts)

  • I = current (in amps)

  • R = resistance (in ohms)

  • P = power (in watts)

    Unknown Value Formula
    Voltage V = IR
    Current I = V/R
    Resistance R = V/I
    Power P = VI or P = V2/R or P = I2R

Electronics Resistor and Capacitor Color Code

In electronic circuits, the value of resistors and capacitors can often be determined by their color and by the digits and multipliers that appear on the casing. The following table outlines values for some common resistors and capacitors.

Color 1st Digit 2nd Digit Multiplier Tolerance
Black 0 0 x 1 ± 20%
Brown 1 1 x 10 ± 1%
Red 2 2 x 100 ± 2%
Orange 3 3 x 1,000 ± 3%
Yellow 4 4 x 10,000 ± 4%
Green 5 5 x 100,000
Blue 6 6 x 1,000,000
Violet 7 7 x 10,000,000
Gray 8 8 x 100,000,000
White 9 9
Gold x 0.1 ± 5%
Silver x 0.01 ± 10%
image0.jpg

Electronics Capacitor Tolerance Code

In electronic circuits, the tolerance of capacitors can be determined by a code that appears on the casing. The code is a letter that often follows a three-digit number (such as 130Z). The following table outlines tolerance values for some common capacitors.

Code Tolerance
B ± 0.1 pF
C ± 0.25 pF
D ± 0.5 pF
F ± 1%
G ± 2%
J ± 5%
K ± 10%
M ± 20%
Z +80%, –20%

Electronics Capacitor Value Reference

In electronic circuits, the value of capacitors can be determined by a two- or three-digit code that appears on the casing. The following table outlines values for some common capacitors. Note that two-digit values are in pico-farads and three-digit values are in microfarads.

Marking Value
nn (a number from 01 to 99) nn picofarads (pF)
101 100 pF
102 0.001 µF
103 0.01 µF
104 0.1 µF
221 220 pF
222 0.0022 µF
223 0.022 µF
224 0.22 µF
331 330 pF
332 0.0033 µF
333 0.033 µF
334 0.33 µF
471 470 pF
472 0.0047 µF
473 0.047 µF
474 0.47 µF
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