A resistor consists of two metal end caps with a resistive material placed in between
as shown in the cross-sectional diagram opposite.
The three common substances used for the resistive material are Carbon, Metal Oxide and Thin Wire.
The electrical symbol for a resistor is shown opposite.
The first two bands give the value in significant figures, the third gives the multiplier and the fourth the tolerance.
e.g for the resistor opposite - green, blue, red and gold - has a value of
5 - 6 - 00 - ± 5% i.e. 5600Ω or 5.6kΩ
Preferred Values
Since exact values of fixed resistors are unnecessary in most circuits, only certain preferred values are made.
The values chosen for the E24 series (with ± 5% tolerance ) are as follows:
1.0, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.7, 3.0, 3.3, 3.6, 3.9, 4.3,
4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2, 9.1, and multiples that are powers of ten.
These values give maximum coverage with minimum overlap with the ± 5% tolerance.
In many applications the E12 series of resistors gives adequate values.
1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2, and multiples that are powers of ten.
If the voltage across the resistor is doubled, then the current is also doubled.
The diagram shows a graph of voltage across and current through a resistor.
As can be seen, the current is proportional to the voltage across the resistor.
