Cheat Sheet

Electronics For Dummies (UK Edition)

Having basic electronics info with you at your electronics workbench in the UK can be invaluable. Tear out and pin up these calculations, values, symbols, abbreviations, measurements and markings, and you’ll always have the essentials at hand.

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

These equations, using Ohm’s Law and Joule’s Law, are the most useful you’ll find in electronics. They come in handy all the time for checking what's going on in your circuits.

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

where:

  • V = voltage (in volts)

  • I = current (in amps)

  • R = resistance (in ohms)

  • P = power (in watts)

Resistor and Capacitor Colour Code

Use this table to decipher the colour code on your resistors and capacitors. Distinguishing some colours from others can be tricky, so examine small parts really closely – perhaps with a magnifying glass and always under good light.

Colour 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
Grey 8 8 x 100,000,000
White 9 9
Gold x 0.1 ± 5%
Silver x 0.01 ± 10%
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Capacitor Tolerance Code

Capacitor ratings aren't all that precise, but you can at least work out how imprecise the ratings are by deciphering the following letter tolerance codes.

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%

Capacitor Value Reference

The first two digits of a capacitor value reference give you a number that you then divide or multiply by factors of ten according to the value of the third digit.

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

Common Electronic Component Symbols in the UK

This table shows you the electrical and electronic component symbols used in the UK. The US and other countries use their own symbols for some components, such as resistors and capacitors.

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Electronic Component Abbreviations

This table lists the abbreviations for some standard international units named after famous scientists and engineers. The symbol for the ohm is the upper case omega, which is the last letter of the Greek alphabet.

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Units of Measure for Electronics and More

These units of measure are used in many different areas, not just electronics. Note that in science and engineering, though, an upper case 'M' represents a million and a lower case 'm' represents a millionth.

Number Name Scientific Notation Prefix Abbreviation
1,000,000,000 1 billion 109 giga G
1,000,000 1 million 106 mega M
1,000 1 thousand 103 kilo k
100 1 hundred 102
10 ten 101
1 1 100
0.1 tenth 10–1
0.01 hundredth 10–2
0.001 thousandth 10–3 milli m
0.000001 millionth 10–6 micro µ
0.000000001 billionth 10–9 nano n
0.000000000001 trillionth 10–12 pico p
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