How to deal with resistors and resistance
Resistors are the most frequently used passive components. Resistors restrict the flow of current in an electrical circuit. If there is a higher resistance in a circuit the flow of current is smaller; when the level of resistance is lowered the flow of current rises. Level of resistance, current and voltage are related to each other by Ohm’s Law. The voltage across a resistor is measured in volts (V), the current across the resistor in A (amps) and the level of resistance is calculated in Ohms (Ω).
Color bands and numerical values
To indicate the resistor value they're marked with a numbered code or with color bands. Axial leaded resistors tend to be labeled using a range of colored bands. The picture above shows an example with 4 color bands. Each color means a number. In case of a 4 band resistor, the initial 3 color bands shows the value of the resistor in ohms and the fourth band reveals the tolerance. It is not possible to make resistors exactly to the wanted value, therefore the fourth band gives away the tolerance on the value expressed in a percentage. A color code calculator might be helpful, which can be found for example on resistorguide.com. Numerical values with 3 numbers are usually applied for coding SMD resistors. The initial 2 numbers show the significant numbers and the 3th number suggests a multiply element in the order of 10. As an example,in case of a code of 202, the code would equate to 20 x 10^2 = 2 kOhm.
The value of resistance of a resistor as well as the right way to write down resistance values
Resistors can be made for a very wide range of resistance value of more than nine orders of magnitude. This value is always expressed in ohms, but not necessarily written this way. Instead, the letter R is often used to indicate Ohms. One more method of making values clearer is to use the letters R, k or M in place of a decimal point, since decimal points typically disappear when a page is photocopied. For example, utilizing these conventions, you would write 15,000 ohm as 15k and 4,400,000 ohm; as 4M4.
