Physics · Ch 11 — Electric Current Through Conductors
Resistors
Resistors
Resistors are components deliberately placed in a circuit to LIMIT the current flowing through a particular path. Commercially, resistors are mainly of two types: CARBON resistors and WIRE-WOUND resistors. High-value resistors are almost always carbon resistors, since they are small, light, and inexpensive to manufacture.
Because a carbon resistor's small cylindrical body is usually too small to print its resistance value and tolerance in numerals, its value is instead marked using a COLOUR CODE, standardised by the Electronic Industries Association (EIA), consisting of a set of coloured bands or rings painted around the body of the resistor (Fig. 11.7). In the common four-band code, the first three bands (grouped closer together) give the resistance value in ohms -- the first two bands each represent a single significant digit, and the third band is the DECIMAL MULTIPLIER by which those two digits are multiplied. The fourth band, set apart with a visible gap from the other three (so a reader knows which end to start reading from), gives the TOLERANCE -- the manufacturing precision of the stated value. …
What this figure shows. A small cylindrical carbon composition resistor drawn with a wire lead protruding straight out from each end, and its cylindrical body painted with FOUR coloured bands/rings running around its circumference, spaced so that three of the bands are grouped closer together near one end and the fourth (tolerance) band is set apart with a visible gap nearer the opposite end -- this gap is what tells a reader which end to start reading the colour sequence from. No specific colours are named on the figure itself; it illustrates the general banded appeara …
Colour | 1st digit | 2nd digit | Multiplier | Tolerance
Black | 0 | 0 | ×10^0 | --
Brown | 1 | 1 | ×10^1 | ±1%
Red | 2 | 2 | ×10^2 | ±2%
Orange | 3 | 3 | ×10^3 | --
Yellow | 4 | 4 | ×10^4 | --
Green | 5 | 5 | ×10^5 | --
Blue | 6 | 6 | ×10^6 | --
Violet | 7 | 7 | ×10^7 | --
Gray | 8 | 8 | ×10^8 | --
White | 9 | 9 | ×10^9 | --
Gold | -- | -- | ×10^-1 | ±5% …
Worked out. Two short worked illustrations of the colour-code table just given. (i) A resistor with bands Yellow-Violet-Orange-Gold is decoded digit by digit: Yellow=4, Violet=7, Orange multiplier=×10^3, giving 47×10^3 = 47000 Ω = 47 kΩ, with Gold giving a tolerance of ±5%, so the resistor's value is stated as 47 kΩ ±5%. (ii) The reverse problem starts from a known resistance value of 330 Ω and works backward to find its bands: 330 Ω is written as 33×10^1, so the first digit 3 is Orange, the second digit 3 is also Orange, and the ×10^1 multiplier band is Brown, followed by an (unstated in this worked pair) tolerance b …