An ideal voltage source is one which maintains a constant voltage at its terminals, irrespective of the current delivered to the network.
Practically a voltage sources has internal resistances and hence, when it delivers a current, there is always an internal voltage drop which increases as the supplies more and more current.
Thus its terminals voltage progressively falls.
Ideal Voltage Source. Practical Voltage Source
An IDEAL CURRENT SOURCE is one which delivers a current of constant magnitude,
totally independent of the external network connected.
In practical, no current source can be ideal, practical current source is always shown with resistance in parallel.
Ideal Current Source Practical Current Source
