What is Voltage & Current Source

What is Voltage Source:

Voltage source is an electronic component that maintains a specified voltage difference across its terminals, independent of the current passing though it. 

A one coulomb charge traveling (from "-" to "+") through a voltage source of five volts gains five joules (J) of energy. Voltage sources therefore can supply electric energy to a circuit, 

E.g. - by "lifting" charges from the ground to a node with higher voltage.

Electrons have electric potential energy. An electron located at ground node has zero energy. Its energy changes as it travels between circuit nodes. Voltage difference (V) between two nodes is the amount of energy a one coulomb charge gains or loses as it travels from one node to the other.

Therefore, the ground provides a reference for all nodal voltages. In case there is no path for an electron to travel from ground to a node, that node and its adjacent components are deactivated and excluded from simulation. Without a ground symbol, the entire circuit is deactivated.

With reference of EveryCircuit you can adjust any circuit parameter with analog knob while simulation is running and see how the circuit responds. Here you can adjust the values of voltage sources and observe the changes in nodal voltages. To bring up the knob, select the voltage source and click the "knob" button. As you play with the circuit you will gain intuition about its operation.

 

Electric Current:

Current is a flow of electric charge, such as electrons moving through a wire. It is measured in amperes (A) and it has a direction. A current source of five amperes transports five coulombs of charge per second. The direction of conventional current is defined to be the direction of the flow of positive charges.

By default EveryCircuit displays conventional current and the moving green dots represent positive charges. Since electrons carry negative charge, they move in the opposite direction. The speed and brightness of the dots represent the amount of current.

To plot a current through a two-terminal component in oscilloscope, select the component and click the "eye" button.

This article is taken from Every Circuit.