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April 1, 2017

Some Mnemonic phrases for remembering Color Codes of Resistor in Electronics.

Identifying Resistors:

The electronic color code is used to indicate the values or ratings of electronic components, usually for resistors, but also for capacitors, inductors, diodes and others. A separate code, the 25-pair color code, is used to identify wires in some telecommunications cables.

Most axial resistors use a pattern of colored stripes to indicate resistance. SMT ones follow a numerical pattern. Cases are usually brown, blue, or green, though other colors are occasionally found like dark red or dark gray.

Resistor Color Codeing: 

Black, Brown, Red, Orange, Yellow, Green, Blue, Violet, Gray, White (Gold Silver).

Mnemonic phrases for remembering color codes of resistor:

There are many mnemonic phrases used to remember the order of the colors. They are, but are not limited to, and variations of: 
  • Bad Boys Ravish Our Young Girls But Violet Gives Willingly.
  • Bad Beer Rots Our Young Guts, But Vodka Goes Well. Get Some Now!  
  • B.B. ROY of Great Britain had a Very Good Wife.
  • Buffalo Bill Roamed Over Yellow Grass Because Vistas Grand Were God's Sanctuary. 
  • Bully Brown Ran Over a Yodeling Goat, Because Violet's Granny Was Gone Snorkeling.
  • Buy Better Resistance Or Your Grid Bias May Go Wrong.
  • Bill Brown Realized Only Yesterday Good Boys Value Good Work.
  • Better Be Ready Or Your Great Big Plan Goes Wrong.
  • Better Be Ready Or Your Great Big Venture Goes West.
  • Black Bananas Really Offend Your Girlfriend But Violets Get Welcomed.
  • Black Birds Run Over Your Biting Visible Gray Worms.
  • Big Boys Race Our Young Girls But Violet Generally Wins.
  • Black Boys Rape Our Young Girls Behind Victory Garden Walls.
  • Black Boys Rape Our Young Girls But Virgins GWithout.


To remember the color bands on resistors in order of increasing magnitude.
  • Numerically the value (0-9) of a resistor via the color-coded bands: Black (0), Brown (1), Red (2), Orange (3), Yellow (4), Green (5), Blue (6), Violet (purple, 7), Gray (8), and White (9).
  • Also, note that the red through violet are the colors of the rainbow (in order). Although the ROY G. BIV mnemonic for rainbow colors includes indigo between blue and violet.

Figure 1: A diagram of a resistor, with four color bands A, B, C, D from left to right.

Figure 2: A diagram of a 2.7 Mega Ω color coded resistor. 

To distinguish left from right there is a gap between the C and D bands.

  • Band A is the first significant figure of component value (left side)
  • Band B is the second significant figure (some precision resistors have a third significant figure, and thus five bands).
  • Band C is the decimal multiplier
  • Band D if present, indicates tolerance of value in percent (no band means 20%)
For example, a resistor with bands of yellow, violet, red, and gold has first digit 4, second digit 7 (violet), followed by 2 (red) zeros: 4,700 ohms. Gold signifies that the tolerance is ±5%, so the real resistance could lie anywhere between 4,465 and 4,935 ohms.
Figure 3: 4.7 Kilo Ω resistor with ±5% tolerance.

All coded components have at least two value bands and a multiplier; other bands are optional.

March 31, 2017

What is a Resistor? What are the Types of Resistors? What are the Applications of Resistor?

What is a Resistor?

A resistor is a passive two-terminal electrical or electronic component that resists an electric current by producing a voltage drop between its terminals in accordance with Ohm's law. The electrical resistance is equal to the voltage drop across the resistor divided by the current through the resistor. 

Figure 1: A typical axial-lead resistor.

Figure 2: Two common schematic symbols of resistor.
In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines, among other uses. High-power resistors that can dissipate many watts of electrical power as heat may be used as part of motor controls, in power distribution systems, or as test loads for generators. Fixed resistors have resistances that only change slightly with temperature, time or operating voltage. Variable resistors can be used to adjust circuit elements (such as a volume control or a lamp dimmer), or as sensing devices for heat, light, humidity, force, or chemical activity.

Theory of Operation:

Ohm's law: The behavior of an ideal resistor is dictated by the relationship specified by Ohm's law:
             V = I/R

Ohm's law states that the voltage (V) across a resistor is proportional to the current (I), where the constant of proportionality is the resistance (R). For example, if a 300 ohm resistor is attached across the terminals of a 12 volt battery, then a current of 12 / 300 = 0.04 amperes flows through that resistor.

Practical resistors also have some inductance and capacitance which affect the relation between voltage and current in alternating current circuits.

The ohm (symbol: Ω) is the SI unit of electrical resistance, named after Georg Simon Ohm. An ohm is equivalent to a volt per ampere. Since resistors are specified and manufactured over a very large range of values, the derived units of milliohm (1 mΩ = 10-3 Ω), kilohm (1 kΩ = 103 Ω), and megohm (1 MΩ = 106 Ω) are also in common usage. 

Figure 3: A few types of resistors.

Types of Resistors:

1.     Linear resistors.
                                 i.         Fixed resistors
a)    Led arrangement
b)    Carbon composition
c)     Carbon Pile
d)    Carbon film
e)    Printed carbon resistor
f)      Thick and thin film
g)    Metal film
h)    Metal oxide film
i)      Wire wound
j)      Foil resistor
k)    Ammeter shunt
l)      Grid resistor
m) Special verities
                                    ii.         Variable resistor
a)       Adjustable resistor
b)       Potentiometers
c)        Resistance and decade boxes
d)       Special devices.
2.     Non-linear resistors.

Applications of Resistors:

  • In general, a resistor is used to create a known voltage-to-current ratio in an electric circuit. If the current in a circuit is known, then a resistor can be used to create a known potential difference proportional to that current. Conversely, if the potential difference between two points in a circuit is known, a resistor can be used to create a known current proportional to that difference.  
  • Current-limiting. By placing a resistor in series with another component, such as a light-emitting diode, the current through that component is reduced to a known safe value.  
  • A series resistor can be used for speed regulation of DC motors, such as used on locomotives and train sets.  
  • An attenuator is a network of two or more resistors (a voltage divider) used to reduce the voltage of a signal.  
  • A line terminator is a resistor at the end of a transmission line or daisy chain bus (such as in SCSI), designed to match impedance and hence minimize reflections of the signal.  
  • All resistors dissipate heat. This is the principle behind electric heaters.  

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Describe a Starter-Motor Circuit.

Figure 1: Typical Starter-Motor Circuit.

A Starter-Motor Circuit: 

Figure 1 shows a very simple diagram of an engine starter-motor circuit. If one day you turn on the ignition switch, push the start button, and nothing happens, this is the circuit diagram you will need. A complete engine wiring diagram would probably contain the same information, but it would also contain all of the meters, idiot lights, and alternator wiring, adding considerable visual confusion.

For the starter-motor circuit all you need to see are the:

  • Battery switch
  • Fuse between battery switch common terminal and engine panel
  • On/Off switch
  • Momentary start switch
  • Wire from starting switch to solenoid
  • Heavy positive cable from battery-select common terminal to solenoid
  • Heavy negative cable from battery negative terminal to engine negative terminal.

If the engine won’t turn over, the problem probably lies somewhere in this diagram. 

Wiring Symbols

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