Fixed resistors

Resistors are manufactured in several kinds, for several different jobs. Three of them matter here.

Fixed resistors

One value, set when it was made, and it cannot be altered.

Variable resistors

Built so the value can be changed whenever you want.

Light dependent resistors

The value changes by itself, according to how much light falls on them.

How a fixed resistor is made

Fixed resistors of various values are produced either by depositing a thin carbon film on an insulating material, or by winding a material of high resistivity such as nichrome wire. Their value cannot be changed.

Figure to be added

Figure 19.23 — several fixed resistors of different values, small cylinders with a wire lead at each end and coloured bands painted round the body.

10 Ω 100 Ω 1.2 kΩ

The circuit symbol

Figure to be added

Figure 19.24 — the circuit symbols used for a fixed resistor: a zigzag line, and a plain rectangle in the line.

The value is printed on it in colour

A resistor is too small to write "1000 ohms" on, so the value goes on in coloured bands instead. Reading them is the subject of the next two pages.