Resistor

A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. 

The most common values are:

•  10Ω, 47Ω,100Ω, 220Ω, 330Ω, 470Ω, 680Ω
• 1kΩ, 2.2kΩ, 3.3kΩ, 4.7kΩ, 10kΩ, 
• 22kΩ, 47kΩ, 100kΩ, 330kΩ, 1MΩ

Resister values colour

You can download a Resistor Values Calculator at:

http://code.msdn.microsoft.com/Resistor-Values-Calculator-cadb6af3

 Types of Resistance;

• Carbon Composition Resistor –Made of carbon dust or graphite paste, low wattage values 
• Wire wound resistor
• Semiconductor Resistor –High frequency/precision surface mount thin film technology
• Carbon film resistor,
• Metal film resistor,
• Metal oxide film resistor,
• Metal glaze resistor.
• Foil resistor.

Data and Specifications

• Resistance values. ohm 
• Power rating. Watts
• TCR (Temperature Co-efficient of Resistance). The rate at which the resistance of the material changes with increase in temperature, normally it is expressed in term of parts per million, per degree Celsius- (ppm/°C).
• Maximum temperature specification- °C
• Maximum Voltage specification - Volts.
• Tolerance.

Understanding Resistors and Temperature

A resistor's Temperature Coefficient of Resistance (TCR) tells how much its value changes as its temperature changes. It is usually expressed in ppm/°C (parts per million per degree Centigrade) units. What does that really mean?

Let's use an example: 50 ohm 100 Series precision resistor has a (standard) TCR of 20ppm/°C. That means its resistance will not change more than 0.000020 ohms (20.1,000,000) per ohm per degree Centigrade temperature change (within the rated temperature range of -55 to +145°C, measured from 25°C room temperature.)

Assume our resistor is in a product that heats up from room temperature to 50°C. To find our 50W resistor's (maximum) change caused by that 25°C rise, multiply 0.000020 times 50 (the resistor value) times 25 (the temperature change.) The resistor's value would change no more than 0.025 ohms. (0.000020 X 50 X 25 = 0.025W.).

Preferred values or E-series

As basis the E12 has been developed. E12 means that every decade (0.1-1, 1-10, 10-100 etc) is divided in 12 steps. The size of every step is equal to:

10^(1/12) = 1.21 

One could also say every value is 21% or 1.21 times higher than the last, rounded to whole numbers. Because of this, all resistors with a tolerance of 10% overlap. The series looks as follows: 1– 1.2 – 1.5 – 1.8 – 2.2 – 2.7 – 3.3 – 3.9 – 4.7 – 5.6 – 6.8 – 8.2 – 10 etc. All these values can be powers of ten (1.2– 12 – 120 etc).

for more information, see:
https://youtu.be/jSPNvJ0XYCQ

The most common series are:

• E6   20%
• E12 10%
• E24 5% (also available with 1%)
• E48 2%
• E96 1%
• E192 0.5% (also used for resistors with 0.25% and 0.1%).

Read more http://www.resistorguide.com/resistor-values/