Basic Guide To Resistors

 

A resistor is an electronic component that is used to resist the flow of electrical current. The resistance restricts the flow of electrons in a circuit. Resistors are known as passive components because they do not require energy to perform, they only use energy.

 This guide will touch upon several topics:

 

  • 1) Units

  • 2) Resistor Colour Codes

  • 3) Ohms Law

  • 4) Power

  • 5) Types of Resistors

 


1) Units:

Electrical resistance is measured in Ohms which uses the Greek symbol omega (). The ability of the material to resist the current flow. Resistance is measured in SI units and being able to understand the size you require is very important.  Resistors can be < 1 Ω or in turn can be Millions of Ω ins size. Additional letter prefixes are used to denote values.

 

1 Ohm 1R
1000 Ohms 1K
1,000,000 Ohms 1M

 

To prevent misreading - decimal points are often replaced with the letter: For example, a 1.5Ω Resistor = 1R5Ω

 

2) Resistor Colour Codes:

  • Resistors are coded with coloured stripes which are used to denote both the resistance value and the tolerance. It is very handy to become familiar with how the colour code system works - however, if you're feeling lazy then give our four band resistor calculator a go!
  • We will explain how to calculate resistor codes in a future blog post!

 

3) Ohms Law:

Ohms law is an important and fundamental rule to remember when working with resistors and electronics in general. It defines the relationship between Voltage - Resistance and Current.  

 

V Voltage in Volts
R Resistance in Ohms ()
I Current in Amps

 

"The potential difference (voltage) across an ideal conductor is proportional to the current through it" 

 

 

 

V

 

 

I

=

___

 

 

 

 

R

 

4) Power:

 

When a resistor is used the process creates HEATGenerally, the amount of heat produced correlates with the voltage and current. Every resistor has a power rating measured in Watts which is the maximum power the resistor can handle without being damaged. The power can be calculated from the voltage across the resistor or the current through it: 

 

 

 

V2

 

 

 

 

 

 

 

 

P

=

___

 

or

 

P

=

I2

x

R

 

 

R

 

 

 

 

 

 

 

 

 

Whereby; P = Power (Watts), I = Current (Amps), V = Voltage (Volts), R = Resistance (Ohms)

 


 

Types of Resistors

 

There are a large variety of variable and fixed type resistors with various construction styles for ech. The two main types of resistors are;

 

  • Fixed Resistors - Most common type and have a constant resistance value. If someone talks about a resistor it will be most likely be this type.
  • Variable Resistors - Have an adjustable resistance value that is normally mechanically adjusted. When used as a voltage divider they are called potentiometers.

 

5) Types of Fixed Resistors:

 

Carbon Film Resistors   A film of carbon is deposited onto an insulated substrate which is then cut into a spiral body. The resistance is controlled by the varying proportion of carbon to insulation. More carbon gives less resistance and more insulation gives more resistance. Carbon resistors tend to be a low cost option.   Carbon Film Resistor
         
         
Metal Film Resistors   A film of metal is sprayed onto a ceramic substrate and is then cut into a spiral body. Factors such as the length, thickness and width of the metal spiral determines the resistance value. Metal film resistors are low noise and are more stable when exposed to thermal changes and applied voltages compared to Carbon Resistors.   Metal Film Resistor
         
         
Metal Oxide Film Resistors   Uses a metal oxide film deposited onto a ceramic rod and protected using an epoxy coating. The resistance can be adjusted by cutting grooves in the film. Metal Oxide have a higher maximum operating temperature than standard metal film resistors.   metal oxide resistors
         
         
Wire Wound Resistors   Primarily used for high power applications, they are made from winding wire onto an insulating core. They have a high level of reliability with a low level of temperature coefficient. These are the oldest type of resistor however they still have have high power ratings and good properties for values of low resistance.   wirewound resistor
         

 

Many more types of resistors are available and would quadruple the length of this guide if included! This guide is intended as a general overview to the basic functions and principles behind resistors. We will look to expand upon this in later guides!

 Check out our range of resistors here

 

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