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.
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.
Ohm continued working for several other Universities throughout Bavaria and published several papers. In two important papers in 1826, Ohm gave a mathematical description of conduction in circuits modeled of Fourier’s study of heat conduction. These papers continue Ohm’s deduction of results from experimental evidence and, particularly in the second paper, he was able to propose laws which went a long way to explaining results of others working on galvanic electricity. This second paper certainly was a first step in a comprehensive theory which Ohm was able to give in his famous book published in the following year called “Die Galvanische Kette, mathematisch bearbeitet” (1827) which means “The Galvanic Chain, Mathematically worked” and contained what is now know as the ‘Ohm Laws’ and they are for voltage: E=IxR, current: I=E/R, resistance: R=E/I, power: P=E 2/R, also P=I2*R or P=E*I
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 lifelo
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 3 until you know the color-code backwards, forwards, and inside-and-out (trust me!)
Can you ‘create’ your own resistors? Sure thing, and not difficult. Here is how to do it: Draw a line on a piece of paper with a soft pencil, HB or 2HB will do fine. Make the line thick and about 2 inches (5cm) long. With your multimeter, measure the ohm’s value of this line by putting a probe on each side of the line, make sure the probes are touching the carbon from the pencil. The value would probably be around the 800K to 1.5M depending on your thickness of the line and what type of pencil lead is used. If you double the line the resistance will drop considerably, if you erase some of it (length-wise obviously!) the resistance will increase. You can also use carbon with silicon glue and when it dries measure the resistance, or gypsum with carbon mixed, etc. The reason for mentioning these homebrew resistors is that this method was used in World War II to fix equipment when no spare parts were available. My father, who was with the Dutch resistance during WWII, at that time made repairs like this on many occasion.
Step 1: Learn the colors
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.
Step 2: Learn the tolerances.
Step 3: Do the exercises below. (Cheating gets you nowhere :-****
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
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