First the history and development of the resistor as we now now it. Georg Simon Ohm was born on March 16, 1789 in the city of Erlangen in Bavaria, which is now Germany. He died on July 6, 1854 in Munich, Bavaria, Germany. Ohm came from a protestant family. His father, Johann Wolfgang Ohm, was a locksmith while his mother, Maria Elizabeth Beck, was the daughter of a tailor. Although his parents had not been formally educated, Ohm's father was a rather remarkable man who had educated himself to a high level and was able to give his sons and excellent education through his own teachings. Had Ohm's brothers and sisters all survived he would have been one of a large family but, as was common in those times, several of the children died in their childhood. Of the seven children born to Johann and Maria Ohm only three survived, Georg, his brother Marin who went on to become a well-known mathematician, and his sister Elizabeth Barbara.

While children, Georg and Martin were taught by their father who brought them to a high standard in mathematics, physics, chemistry and philosophy. This was in stark contrast to their school education. Georg Simon entered Erlangen Gymnasium at the age of eleven but there he received little by the way of scientific training. In fact, his formal part of his schooling was uninspired stressing learning by rote and interpreting texts. This contrasted strongly with the inspired instruction that both Georg Simon and Martin received from their farther who brought them to a level in mathematics which led the professor at the University of Erlangen, Karl Christian von Langsdorf, to compare them to the Bernoulli Family. It is worth stressing again the remarkable achievement of Johann Wolfgang Ohm, an entirely self-taught man, to have been able to give his sons such a fine mathematical and scientific education.

In 1805 Ohm entered the University of Erlangen but he became rather carried away with student life. Rather than concentrate on his studies, he spent much time dancing, ice skating and playing billiards. Ohm's father, angry that his son was wasting the educational opportunity that he himself had never been fortunate enough to experience, demanded that Ohm leave the university after three semesters. Ohm was sent to Switzerland where, in September 1806, took up a post as a mathematics teacher in a school in Gottstadt bei Nydau.

At the time Ohm started to write his papers (8) he was on a one year sabbatical doing his research at the Jesuit Gymnasium of Cologne.

In 1849 Ohm took up a post in Munich as curator of the Bavarian Academy's physical cabinet and began to lecture at the University of Munich. Only in 1852, two years before his death, did ohm achieve his lifelong ambition of being appointed to the chair of physics at the University of Munich.

Another example for a Carbon 22000 Ohms or 22 Kilo-Ohms also known as 22K at 5% tolerance:

Band 1 = Red, 1st digit

Band 2 = Red, 2nd digit

Band 3 = Orange, 3rd digit, multiply with zeros, in this case 3 zero's

Band 4 = Gold, Tolerance, 5%

Example for a Precision Metal Film 19200 Ohms or 19.2 KiloOhms also known as 19K2 at 1% tolerance:

Band 1 = Brown, 1st digit

Band 2 = White, 2nd digit

Band 3 = Red, 3rd digit

Band 4 = Red, 4th digit, multiply with zeros, in this case 2 zero's

Band 5 = Brown, Tolerance, 1%

Band 6 = Blue, Temperature Coefficient, 6

If you are a bit serious about the electronics hobby I recommend learning the "Color-Code". It makes life a lot easier. The same color code is used for everything else, like coils, capacitors, rf-chokes, etc. Again, just the color code associated with a number, like: black=0 brown=1 red=2, etc, etc.

If you are interested in learning the code by memory, try the steps below to help you 'Learn the Color-code'.

Make sure you add the number to the color, like: 0 is black, 1 is brown, 2 is red, etc. etc.

Do not proceed to step

Can you

The color 'Gold' is not featured in the above table. If the 3rd band is gold it means multiplying by 0.1. Example, 1.2 ohm @ 5% would be brown-red-gold-gold. 12 multiplied by 0.1 gives 1.2 Don't get confused by gold as a resistance or a tolerance value. Just watch the location/posistion of the band.

Colors I used for 'Gold, Orange, Gray, and Silver'

1st band, denominator: Brown (1) 2nd band, denominator: Black (0) 3rd band, how many zeros (1) 4th band, tolerance in %: gold (5) Answer: 1 0 1 = 100 ohm, 5% tolerance

1st band: _____ 2nd band: _____ 3rd band: _____ 4th band, tolerance in %: _____ Answer: ___________________

1st band: _____ 2nd band: _____ 3rd band: _____ 4th band, tolerance in %: _____ Answer: ___________________

1st band: _____ 2nd band: _____ 3rd band: _____ 4th band, tolerance in %: _____ Answer: ___________________

1st band: brown (1) 2nd band: black (0) 3rd band: gold (0.1) 4th band, tol. in %: red (1-0-0.1 = 1 ohm, 2%)

1st band: 2nd band: 3rd band: 4th band, tolerance in %: Answer: ___________________

1st band: 2nd band: 3rd band: 4th band, tolerance in %: Answer: ___________________

1st band: brown (1) 2nd band: white (9) 3rd band: yellow (4) 4th band: brown (0) 5th band, tol.in %: brown (1940 ohm = 1.94K, Precision type.)

1st band: 2nd band: 3rd band: 4th band: 5th band, tolerance in %: Answer: ___________________

To get familiarized with abreviations in values, I used below 4700 or 4K7, 1000 or 1K, which is all the same. Every thousand (1000) is called a 'K' which stands for 'Kilo'. The 'M' stands for 'Mega' (million). 1 Mega is 1000K or 1000 000 ohms. So 4K7 means 4 thousand and 7 hundred or 4700 ohms. 6K8 means 6 thousand and 8 hundred or 6800 ohm. One more example, 1M2 means 1million and 200.000 or 1.200000 ohms. Here are a couple more: 1K92=1.92K=1920 ohms, 100E=100 ohms, 19K3=19.3K=19300 ohms, 1M8=1.8M, etc., etc. These abreviations you find everywhere in the industry, schematics, diagrams and whatever. It is normal and takes a bit of time to get used to.

This should get you started. If it looks difficult to you, don't worry. It is easy. Whenever you have a spare moment practise the color code in your head. It's like learning to ride a bicycle, once you know how to do it you never forget. I, and many others who learned electronics in the 60's and up to the 80's, were taught a little sentence to remember the sequence of the resistor colors like Black, Brown, Red, Orange, Yellow, Green, Blue, Violet, Gray, and White, which refers to: "4700 ohm, 5% = yellow violet red, gold 100 ohm, 2% = brown black brown, red 1000 ohm, 5% = brown black red, gold 22 ohm, 1% = red red black, brown150 ohm, 5% = ________________________ 270 ohm, 5% = ________________________ 3300 ohm, 5% = ________________________ 10 ohm, 1% = ________________________ 470 ohm, 2% = ________________________ 6800 ohm, 10% = ________________________ 3K3, 5% = ________________________ 1K, 5% = ________________________ 150 ohm, 1% = ________________________ 2M9, 10% = ________________________ 10M, 10% = ________________________ 1 Mega Ohm, 5% = ________________________ 1 ohm, 1% = ________________________ 3M9, 20% = ________________________ 1200 ohm, 5% = ________________________ 1K2, 5% = ________________________ 220 ohm, 1% = ________________________ 3300 ohm, 2% = ________________________ 47 ohm, 5% = ________________________ 390 ohm, 5% = ________________________ 3900 ohm, 2% = ________________________ 100.000 ohm, 5% = ________________________ 10K, 5% = ________________________ 10.000 ohm, 5% = ________________________ 1500 ohm, 2% = ________________________ 56K, 5% = ________________________ 1M, 10% = ________________________ 470K, 1% = ________________________ 1.8 ohm, 2% = ________________________ 2.2 ohm, 1% = ________________________ 2K76, 1% = ________________________ 94.1K, 2% = ________________________

Good luck my friends!

What exactly is rho you ask? Ohm's Law is not a fundamental law like Newton's Laws or the laws of thermodynamics, but an empirical description of a property shared by many electrical materials. This property of electrical materials is called conductivity. The inverse of that is called

This is also called the reciprocal. B is the reciprocal of A, so that A*B = 1.

The relationship between conductivity and resistivity is: conductivity = 1/resistivity

Resistivity, represented by the greek letter

In plain English words, resistance, R, is the ratio of the length (L) of the conductor wire divided by the constant conductivity (the greek sigma ) and by the cross sectional area (A). This formula is used to calculate how much resistance will be present in a wire conductor. You will find that it is important to reduce the resistance in the conductors in circuits. This is because resistance generates heat, and, for many circuits, heat is not desireable. So this formula shows us that one way to do this is to keep the length of conductors to a minimum. That also saves money. Reducing the length of conductors in a circuit will reduce the heat radiated which will keep nearby electronics components from overheating [thus helping them to last longer] and reduce power requirements [== save a little money over time]. Wow! All that information is derived from that one little formula. Formulas are powerful tools.

(Tony's note: The Rho explanation was taken from "BASIC ELECTRONICS ENGINEERING TECHNOLOGY 4.1" and is used with permission from Jairo Moreno).

I forgot to mention a very important thing, there are two resistor

In the case of surface mount resistors; since they are so tiny they feature the same coding as on capacitors. For example, if it says 103 this means 10 Kilo-ohm (10 + 3 zeros), 104 means 10 + 4 zeros (100K), 222 means 22 + 2 zeros (2K2). Easy huh?

E24 Standard Series Values (5%)1.0 10 100 1.0K (1K0) 10K 100K 1.0M(1M0) 10M 1.1 11 110 1.1K (1K1) 11K 110K 1.1M(1M1) 11M 1.2 12 120 1.2K (1K2) 12K 120K 1.2M(1M2) 12M 1.3 13 130 1.3K (1K3) 13K 130K 1.3M(1M3) 13M 1.5 15 150 1.5K (1K5) 15K 150K 1.5M(1M5) 15M 1.6 16 160 1.6K (1K6) 16K 160K 1.6M(1M6) 16M 1.8 18 180 1.8K (1K8) 18K 180K 1.8M(1M8) 18M 2.0 20 200 2.0K (2K0) 20K 200K 2.0M(2M0) 20M 2.2 22 220 2.2K (2K2) 22K 220K 2.2M(2M2) 22M 2.4 24 240 2.4K (2K4) 24K 240K 2.4M(2M4) 2.7 27 270 2.7K (2K7) 27K 270K 2.7M(2M7) 3.0 30 300 3.0K (3K0) 30K 300K 3.0M(3M0) 3.3 33 330 3.3K (3K3) 33K 330K 3.3M(3M3) 3.6 36 360 3.6K (3K6) 36K 360K 3.6M(3M6) 3.9 39 390 3.9K (3K9) 39K 390K 3.9M(3M9) 4.3 43 430 4.3K (4K3) 43K 430K 4.3M(4M0) 4.7 47 470 4.7K (4K7) 47K 470K 4.7M(4M7) 5.1 51 510 5.1K (5K1) 51K 510K 5.1M(5M1) 5.6 56 560 5.6K (5K6) 56K 560K 5.6M(5M6) 6.2 62 620 6.2K (6K2) 62K 620K 6.2M(6M2) 6.8 68 680 6.8K (6K8) 68K 680K 6.8M(6M8) 7.5 75 750 7.5K (7K5) 75K 750K 7.5M(7M5) 8.2 82 820 8.2K (8K2) 82K 820K 8.2M(8M2) 9.1 91 910 9.1K (9K1) 91K 910K 9.1M(9M1)