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The Colour Code for Resistors (and Capacitors)
Resistance is measured in Ohms (Ω)  
1k means 1000Ω and 1M means 1000000Ω
The number of Ohms resistance is (usually) indicated by a series of coloured bands on the resistor.  
   
 
   
Most resistors have four coloured bands as shown above.  
To find the resistance, start with the coloured band which is nearest to the end of the resistor.  
   
The first two bands tell us the first two digits of the number of Ohms.  
The third band tells us the power of 10 by which the first two digits are multiplied.  
   
So, in the example illustrated above, the resistance is:  
  2 (red)  
  7 (violet)  
  multiplied by 104 (yellow).  
That is, 27104 or 270000 or 270k.  
   
For very low resistances, there are two other colours for the third band: silver for -1 and gold for -2.  
So, for example, if we replaced the yellow band with silver, we would have 2710-1 or 2.7Ω  
   
The last colour (again, silver or gold) indicates the tolerance or precision of the manufacturing process.  
Silver means 10% and gold 5%  
   
Some capacitors also use this system in which case the colour code usually gives the capacitance in pico-Farads (1pF = 10-12F) and the last band indicates the voltage rating of the capacitor.  
   
More commonly, the capacitance is written on the component, though often still in a slightly coded way.  
For example, a capacitor of 4700pF could be labelled, 4700pF (no surprise there) or just 4700 or 4.7n (for nano, 10-9) or 4n7.  
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