Resistors come in a variety of shapes and sizes. They are used in electronics to limit current and divide voltages that in turn controls sound and light levels and frequencies.
All resistors dissipate electrical energy and create heat.
Resistors are rated by the resistance value BUT  take care if you are making a replacement they are also given power ratings .5 W , 1 W, 10 W etc.


Small carbon/clay resistors are common in electronics the internal carbon to clay ratio determines the resistance.
The physical size will determine the amount of power they can dissipate in the form of heat.

Fixed resistor symbol

Variable Resistor Symbol

Common resistors have 4 bands on them.
Band 1 is closest to one end.
The bands tell you resistance and tolerance (quality)




Resistor Colour Code Calculator | 2 | 3 |









 These are wire wound high power use resistors designed to dissipate lots of heat.





















Resistor Colour Code Calculator | 2 | 3 |


Wire wound resistors are used in higher power (won't melt) where power is being dissipated.

Miniaturization has led to the development of surface mount components such as the surface mount resistors above.

Variable resistors are used in electronic circuits that control varying light speed temperature etc. levels. They function as voltages dividers in most circuits.



slider type variable resistor

 click to enlarge

internal view of variable
resistor  (potentiometer)









The photon sensitive CdS photoresistor is a very common component for sensing light levels in automated lighting systems.
As light intensity increases on the cadmium sulphide element the resistance drops.
In a sense this device acts much like a variable resistor that is activated by light.

You have probably seen them on night lights in the home or in industrial units that you have installed.


Notice that when light intensity increases the resistance decreases.

Can you spot the CdS cell in this night light?
Resistor Colour Code Calculator | 2 | 3 |


Try a few examples until you get the feel of how the colour code works.
Thermal  resistors change resistance as the temperature changes.
Resistance can signal temperature to a control system
Resistance usually increases with increases in temperature.

Maybe your microwave oven has a thermistor probe to help to help determine the internal temperature of cooking food.