Appendix A 1

Appendix A: Color Code forResistors

The electrical resistance of resistors is often marked using colored bandspainted on the resistor. The color of the bands and their sequence indicatethe resistance of the resistor in units of ohms (Ω). The first and secondbands (see Figure 1) give the first and second significant figures of the resis-tance. The third band gives the power-of-ten multiplier. The fourth band(if present) gives the percent tolerance of the resistor.

Third Band

Fourth Band Second Band

First Band(1st significant figure)

(2nd significant figure)

(multiplier)

(Tolerance)

Figure 1: Color code bands

The uncertainty in the value of the resistance is thus the percent tol-erance (expressed as a decimal fraction) times the value of the resistanceobtained from the first three color bands. The actual resistance of the re-sistor should be between “the color-code value minus the uncertainty” and“the color-code value plus the uncertainty.” For example, suppose the colorcode indicated that the resistor should be 2000 Ω with a 10% tolerance. Theactual value of the resistance should lie between 1800 Ω and 2200 Ω.

The numbers to be associated with the various colors of the bands areshown in Table A. As an example, suppose the color bands on a resistorwere red (2), blue (6), yellow (104), and gold (5%). The resistance would be26×104 Ω, plus or minus 5%. This would normally be written as 260 kΩ±5%.If the colors were brown (1), red (2), and green (105), with no fourth band(colorless), the resistance would be 12 × 105 Ω, plus or minus 20%. Thiswould usually be written as 1.2 MΩ ± 20%.

Appendix A 2

TABLE A: COLOR CODE FOR RESISTORS

Color Number Multiplier Tolerance (%)

Black 0 1

Brown 1 101

Red 2 102

Orange 3 103

Yellow 4 104

Green 5 105

Blue 6 106

Violet 7 107

Gray 8 108

White 9 109

Gold 10−1 5%

Silver 10−2 10%

Colorless 20%

1 kΩ = 103 Ω

1 MΩ = 106 Ω

1

Appendix B: Schematic Symbols

A

+ -

V

G

Resistor

Capacitor

Inductor

Fuse

Light BulbSwitch

Diode Voltmeter

Ammeter Galvanometer

Battery or Power Supply AC Power Supply

Figure 2: Color code bands

1

Appendix C: Meters

Very often a conductor is specifically designed to impede the currentwhich flows through it. In this case, the conductor is called a resistor. Whena resistor is part of an electrical circuit, the voltage across the resistor ismeasured by connecting a voltmeter in parallel with the resistor. The currentthrough the resistor is measured by connecting an ammeter in series withthe resistor. How these measurements are made is shown in Figure 1.

Note: Do not confuse the connection of an ammeter with the connectionof a voltmeter. An ammeter should NEVER be connected in parallel witha resistor in a circuit. This would provide a low resistance path aroundthe resistor and could draw a large current from the voltage source, andmight damage or destroy the ammeter. Often, a shorting switch is placedin parallel with the ammeter to protect against such a misconnection. Theshorting switch must be opened (depressed) in order to read the currentflowing in the circuit.

When using ammeters and voltmeters in dc circuits, proper polarity mustbe observed. Proper polarity means that the positive (+) terminal of theinstrument is connected to a more positive electrical potential (voltage) thanthe negative (−) terminal of the instrument. If the terminals are reversed,the needle on the instrument will attempt to go backwards.

V

+ - + -AI R

Figure 3: Proper connection of an ammeter and voltmeter