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Voltage and Current

Posted on : Fri , 01 2014 by : virusi
There are two Quantities that we like to keep track of in electronic circuits: voltage and current. These are usually changing with time; otherwise nothing interesting is happening.

Theory on Voltage :


Voltage (symbol V which stands for Volts or sometimes E which stands for electromotive force (EMF)) is the difference in charge between two points from the more negative point (lower potential) to the more positive point (higher potential). This current continues to flow until all the extra negative charges on the negative side of the circuit have moved to the positive side. When that has happened, both sides of the circuit become electrically neutral and the current stops flowing.
The unit of measure is the volt, with voltages usually expressed in volts (V), kilovolts (1kV =
 10^{3}
V), milivolts (1mV =
10^{-3}
V), or microvolts(1µV =
10^{-6}
V).
A joule of work is needed to move a coulomb of charge through a potential difference of one volt. The coulomb is the unit of electric charge, and it equals the charge of
6*10^{18}
electrons, approximately. Important: Always refer to voltage between two points or across two points in a circuit. To say something like “the voltage through a resistor …” is nonsense, or worse. However, we do frequently speak of the voltage at a point in a circuit. This is always understood to mean voltage between that point and “ground,” a common point in the circuit that everyone seems to know about. Ground or earth may is the point in an electrical circuit from which other voltages are measured, or a common return path for electric current.
You can find out how much voltage exists between two points by using a device known as a voltmeter, which has two wire test leads that you can touch to different points in a circuit to measure the voltage between those points.

Theory on Current :


Current (symbol I which stands for current) is the rate of flow of electric charge past a point. The unit of measure is the ampere (A), or amp, with current usually expressed in amperes (A), milliamperes (1mA =
 10^{-3}
A),microamperes(1µA =
 10^{-6}
A), nanoamperes (1nA =
 10^{-12}
A)).
A current of one ampere (A) equals a flow of one coulomb of charge per second. By convention, current in a circuit is considered to flow from a more positive point to a more negative point, even though the actual electron flow is in the opposite direction.
Important: Always refer to current through a device or connection in a circuit.

Practical Example :


If you don’t see the example below than you should follow this steps:

– Allow Java SE 7 in your browser.

– 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).

Sorry, you need a Java-enabled browser to see the simulation.
It is a simple example in which we have connected a 5V source and 100 ohm resistance and you have 2 diagrams. 1 diagram is showing the current which is flowing throw the resistor and the current sense. 2 diagram is showing the amount of voltage that is flowing throw the resistor. If you want to change the resistor value or the Voltage from the source you should double click on the object and insert a value. If you are interested in how the resistors works than go to everything about resistors .
Last updated on Mon , 03 2014
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One comment on "Voltage and Current"

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