Ohm’s Law
Probably the most important law in electronics is Ohm’s Law. Ohms Law states that the voltage across a resistor equals the resistance of the resistor times the current flowing through it (V=R*I). Thus if you have a resistance of 1000 ohms and a current of 10 milliamps flowing through it, the voltage over it will be: 1000 * 0.01=10V. Ohms law can be expressed in the following ways:
| V | = R * I |
| R | = V / I |
| I | = V / R |
To see some basic examples of Ohms law, browse to the resistors section.
Precision
It is usually not necessary to be very precise in the calculation of the values, thus I will use approximations most of the time. The reason is that the components we normally use have quite a wide tolerance, e.g. the resistors will mostly be 5% and capacitors about 20%. Thus you can see that using values correct up to 10 digits is just a waste of time.
Notation
Here is a summary of commonly used values for electronic components:
| Abbreviation | Name | Value |
| p | pico | 0.000 000 000 001 (1e-12) |
| n | nano | 0.000 000 001 (1e-9) |
| u | micro | 0.000 001 (1e-6) |
| m | milli | 0.001 (1e-3) |
| K | kilo | 1 000 (1e3) |
| M | mega | 1 000 000 (1e6) |
| G | giga | 1 000 000 (1e9) |
For the components that most hobbyist will use, you will see kilo and mega used for resistors; pico, nano and micro for capacitors and micro and milli for inductors.
Shorthand notation
Here are a few guidelines used in industry to write the values of components:
- The value of a capacitor ends with an F (Farad)
- The value of an inductor ends with an H (Henry)
- The value of a resistor ends with an R if smaller than 1000 Ohm, otherwise it is omitted
- Instead of a comma for a resistor of say 4,7 kilo Ohm, use the ‘K’ to indicate the comma (4K7)
A few examples:
| A resistor of 10 000 Ohm | 10K |
| A resistor of 4 700 000 Ohm | 4M7 |
| A resistor of 1 Ohm | 1R |
| A resistor of 0.25 Ohm | 0R25 |
| A capacitor of 0.004 700 Farad | 4700uF |
| An inductor on 0.010 Henry | 10mH |