## Resistors

##### Posted on : Sat , 12 2013 by : virusi

## Some Historical Data :

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. 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.

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. 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=I*R, 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 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.

## Resistor Symbol and Markings :

The symbol for a resistor is shown in the following diagram (The ‘box’ symbol for a fixed resistor is popular in the UK and Europe. A ‘zig-zag’ symbol is used in America and Japan) :

Maximum resistor value = 4700 + (4700*0.05) = 4700 + 235 = 4935 ohms

Minimum resistor value = 4700 – (4700*0.05) = 4700 – 235 = 4465 ohms

As you can see our resistor value can vary from 4935 ohms to 4435 ohms, so if in your application you need a very precise resistor you will have to chose a resistors with a small tolerance value.

## Theory of operation :

Let’s take a look how the current, voltage ant the power are calculated for a resistor. The behavior of an ideal resistor is dictated by the relationship specified by Ohm’s law:

\large V = I * R(1)

\large I = \frac{V}{R}(2)

\large P=I^2*R=I*V= \frac{V^2}{R}(3)

As you know the current that will flow throw a resistor is equal to:

\large I= \frac{V}{R} = \frac{5V}{4700Ω}=0.00106A or 1.06 mA(4)

Now let’s calculate the power that is consumed by a resistor as you already know the power consumed by a resistor equals to:

\large P = \frac{V^2}{R} = \frac{5^2 V}{4700Ω} = \frac{25V}{4700Ω} = 0.0053W or 5.3 mW(5)

More formulas that can be derived from the one mentioned before (Ohm’s law and Joule’s first law) are illustrated in the image below:

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– Lower you java security settings (Go to Control Panel >> Java >> Security and set the security level to medium) .

– Edit Site List (Go to Control Panel >> Java >> Security and click on Edit Site List… and add eagerlearning.org in the list).

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