RESISTORS

RESISTORS

Resistors determine the flow of current in an electrical circuit. Where there is high resistance in a circuit the flow of current is small, where the resistance is low the flow of current is large. Resistance, voltage and current are connected in an electrical circuit by Ohm’s Law.

When a resistor is introduced to a circuit the flow of current is reduced. The higher the value of the resistor the smaller/lower the flow of current.

Resistors are used for regulating current and they resist the current flow and the extent to which they do this is measured in ohms (Ω). Resistors are found in almost every electronic circuit.

The most common type of resistor consists of a small ceramic (clay) tube covered partially by a conducting carbon film. The composition of the carbon determines how much current can pass through.

           

Resistors are too small to have numbers printed on them and so they are marked with a number of coloured bands. Each colour stands for a number. Three colour bands shows the resistors value in ohms and the fourth shows tolerance. Resistors can never be made to a precise value and the tolerance band (the fourth band) tells us, using a percentage, how close the resistor is to its coded value. The resistor on the left is 4700 ohms.

COLOR	DIGIT	MULTIPLIER	TOLERANCE	TC
Silver		x 0.01 W	±10%
Gold		x 0.1 W	±5%
Black	0	x 1 W
Brown	1	x 10 W	±1%	±100*10-6/K
Red	2	x 100 W	±2%	±50*10-6/K
Orange	3	x 1 kW		±15*10-6/K
Yellow	4	x 10 kW		±25*10-6/K
Green	5	x 100 kW	±0.5%
Blue	6	x 1 MW	±0.25%	±10*10-6/K
Violet	7	x 10 MW	±0.1%	±5*10-6/K
Grey	8	x 100 MW
White	9	x 1 GW		±1*10-6/K