Electronics Introduction

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.


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.


Here is a summary of commonly used values for electronic components:

ppico0.000 000 000 001 (1e-12)
nnano0.000 000 001 (1e-9)
umicro0.000 001 (1e-6)
mmilli0.001 (1e-3)
Kkilo1 000 (1e3)
Mmega1 000 000 (1e6)
Ggiga1 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 Ohm10K
A resistor of 4 700 000 Ohm4M7
A resistor of 1 Ohm1R
A resistor of 0.25 Ohm0R25
A capacitor of 0.004 700 Farad4700uF
An inductor on 0.010 Henry10mH