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Resistors

A resistor is something that has resistance.  In electronics, it usually refers to a small component that has a specific resistance.  Electronic companies make many different resistors with different resistances.  So if we need say 470 W, we could go the shop and buy a resistor with a resistance of 470 W.  A common type of resistor looks like this, with a small cylinder and two wires sticking out from two ends:
Of course, it is not possible for companies to make every possible resistances.  There is an infinite number of them.  They just make a range of different resistances.  If they don't sell a resistance that we need, we can try to combine different resistors to make up something close.

There are many types of resistors, and not all of them look like the picture above.  Some of them have the values of their resistances written on them.  Their resistances can also be coded in colour.  The above picture shows one common way to do it: 3 rings of colour close together and a 4^th one a bit further away.  For the 3 rings close together, each colour represents a number:

black	0
brown	1
red	2
orange	3
yellow	4
green	5
blue	6
violet	7
grey	8
white	9

The above picture shows red, violet and yellow.  The numbers are 2, 7 and 4.  This is supposed to make up the number with digits 2 and 7 followed by 4 zeros: 270000 W.  So the first two colours give the first two digits and the third colour gives the number of zeros.

The ring of colour further away tells us the tolerance, or how accurate this value is.  Suppose that the first three colour tells us that the resistance is 270000 W.  The actual resistance can be bigger or smaller.  In other words, there would be an error.  If the company makes the resistance more accurate, they must spend more time and money.  So instead of always making it very accurate, they make a range with different accuracies for different uses.  So a less accurate one could be cheaper.  The colour coding for this tolerance is:

silver	±10%
gold	±5%
red	±2%
brown	±1%

In the picture above, the colour of the last ring is gold.  This is an tolerance of ±5%.  It means that the actual resistance can be up to 5% bigger or smaller than 270000 W.