The RJ Journal - Electronics

A resistor is a component that introduces a resistance in an electric circuit. It makes it harder for the current to flow in the circuit. The higher the resistor value, the harder it is for the current to flow. Reference to a resistor in text or schematic diagrams is done with the letter R. Resistance is measured in ohm which in text is written with the Greek omega character - Ω. So if resistor number 3 in a schematic diagram has the value of 560 ohm it can be written as R3=560Ω.

Two types of symbols are used in schematic diagrams for resistors, the European IEC symbol and the non European symbol. Since I am from Europe I will use the IEC symbols in schematic diagrams.

By hindering the current, the resistor also creates a voltage drop over it. It can be said that the electric potential, the voltage, is higher before the resistor in the circuit, than after it. In analogy with the closed water pipe system, a resistor can bee seen as a reducing valve. The pressure is high before the valve and lower after it. The water flow is also decreased after the valve.

Now is a good time to introduce the formula for voltage current and resistance:

U=R*I which is the same as R=U/I which is the same as I=U/R.

Where U = voltage, R = resistance and I = current.

The voltage over a resistor can be calculated if the current and resistance is known.
The resistance can be calculated if the voltage over the resistor and the current through it is known.
The current through a resistor can be calculated if the voltage over it and its resistance is known.

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