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Resistors in Series and in Parallel

There are two simple forms of electric circuits; the series circuit provides a single conducting path, and the parallel circuit provides more than one. A battery and a single lamp  is an example of the simple circuit. If a second lamp  is added in series the circuit would appear as follows:

 

 

 

Example of Simple Series Circuit

Kirchoff’s Second Law).   Both lamps share the same current.   Another interesting observation, if one of the lamps burns out, the other lamp will also go out because the burnt lamp has now opened the circuit. Another observation, if the lamp specification calls for 12 volts, the 6 volts across each lamp will reduce the illumination. Hence, this circuit as applied to Model train layouts is not very desirable.

Note:  When the switch is closed the 12 volt battery will light both lamps, however each lamp will be dimmer because the ½ of the 12 v battery voltage will appear across each lamp assuming the lamps are identical.

Example of Simple Parallel Circuit

Note:  When the switch is closed the 12 volt battery will light both lamps, however each lamp will be glow with the same intensity because the 12 v battery voltage will appear across each lamp.

 The current from the Battery must be split between Lamp1 and Lamp 2. (Kirchoff’s First Law) Therefore, the Battery must supply twice the current as that supplied in the previous example (series circuit) to the rest of the circuit. This circuit can be a limitation, if your dc source cannot supply the current.

Another interesting observation, if one of the lamps burns out, the other lamp will not go out because the burnt lamp has not interrupted the current going to the other lamp. This application is appropriate for Model Train Layouts.

Resistors In Series

In the following sketch two resistors are in series. Let’s find the total resistance.


Total Value of the Resistance = R1 + R2 in Ohms

Resistors In Parallel

In the following sketch two resistors are in parallel. Let’s find the total resistance.

Total Value of the Resistance = 1/R1 + 1/R2 in Ohms

If you wish to acquire a better understanding of Electronics Theory, I suggest you go to  the following  link: Electronics


In general, the following vendors are recommended for any of the above electronic components:

Radio Shack (Local Store or on-line at  www.radioshack.com)

Futurlec at  www.futurlec.com

DeMar Electronics at  www.demarelectronics.com/

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