Voltage,Current and Resistance.

Voltage imageThis post has concept enforcing videos!Click here(Users outside China) or here (Users in China) to check them out.

Voltage,current and resistance are basic quantities in all electrical circuits.To get off on the right foot in this series of circuit analysis,we have to make sure these concepts are nailed down.And …,nailed tight!

I.Basic concepts.


From basic physics,we know that like charges repel and opposite charges attract.If a positive and negative charge are in proximity,they tie themselves together.To move them some distance apart,some work must be done.The quantity we get when we divide that amount of work (in Joules) by the number of charges we have moved(in Coulombs) is called Voltage.
Where is the voltage in volts(V), is Energy in Joules(J)and is the charge in Coulombs(C).
Voltage is the driving force in electric circuits and is what establishes current.


Voltage provides energy to charges(electrons),allowing them to move through a circuit.The number of charges that pass through a section of conductive material per unity of time is called current.Here is a way you may put it,whenever you apply voltage across a circuit,current flows.

Where is current in Amperes (A), is the charge in Coulombs (C) and is time in seconds (s).


Resistance in an electric circuit is the opposition to the flow of current;it is expressed in Ohms.

3.1 The resistance device–the resistor

The resistor is an electronic component designed to have a certain amount of resistance in an electric circuit.Its common applications include current limiting,voltage dividing,and sometimes heat generation.Resistors come in different shapes and flavors but they are commonly classified in two main categories:fixed and variable.

II.Voltage and current sources

1.Voltage source.

Think of a voltage source simply as a black box that can provide a constant voltage.Some are fixed and some are adjustable.For example,the one in my laboratory can be adjusted anywhere between 0V and 30VDC. Voltage sources can be DC(Direct current) or AC(Alternating current). AC voltage sources will be covered later in the series.

DC Voltage Source

DC voltage source

AC voltage source

AC Voltage source

2.Current source.

The current source may also be thought of as a black box that can provide a constant current to any load.

Current source

Current Source

III.Basic electric circuit

A basic electric circuit is an arrangement of physical components that use voltage,current and resistance to accomplish some useful function.It consists of a voltage source,a load and a path for current between the source and the load.Circuit schematics can be used to represent each component of the electric circuit.

Electric circuit

Electric circuit

In the figure,the source(battery),the path for current which is the copper wire connecting components and the load (lamp) can be seen.A switch is often added to achieve control functionality.

This simple circuit model is fundamental to any circuit design and implementation ;it should be understood before venturing in more complex and advanced designs.



1. Short- circuit and Open -circuit .

Open-circuit and short-circuit are terms you are sure going to be encountering often in your circuit design and analysis journey.A clear understanding of these concepts is vital to safe design and successful troubleshooting!

Short-circuit is a term we use to mean that,in the circuit loop ,current is going back to the source without passing through the load.It causes over -current in the circuit loop and electric components are damaged by excessive heat build-up.Short-circuits should be avoided in any circuit design.

Open -circuit refers to the case when for some reason ,the circuit loop has been broken and there is no path for current.

Short circuit


Open -circuit






We have put together a set of videos to enforce the concepts of voltage,current and resistance and packaged them in the voltage current and resistance videos page.!Click here(Users outside China) or here (Users in China) to check them out!

The concepts covered in this section are fundamental in any electricity related engineering field.It is a good idea to make sure you absorbed as much as possible of the material .Do not hesitate to ask questions on what may seen unclear or point out changes that would make blikoon a better place to learn from.We love to hear from you!

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Daniel Gakwaya loves computer Hardware/Software.He is a Software Engineer at BLIKOON and lead developer of bliboard-The whiteboard system currently marketed by the company.He is known to hack around on any piece of tech that happens to pick his interest. More on his tech endeavors here
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