Ideal voltage source: Whatever amount of current is drawn from it the
voltage at the terminals is always same. *Whenever the terminals are
short circuited (resistance of
between the terminals) the
infinite amount of current flows to maintain voltage. This is
hypothetical condition, why?*

Ideal current source: Whatever load or network of elements is connected
to source, the current pumped by the source into the load always remains same. *Whenever the terminals are open circuits (Terminals are not connected to
any thing) the voltage across the terminals becomes to
maintain the same amount of current through terminals. This is also
hypothetical condition, why?*

Can I leave a current source as shown in figure 3.3?

In this case, voltage across the terminals will be .

__Non Ideal Voltage Source:__ See the circuit in figure
3.4. A non ideal voltage source is modeled with an internal
resistance of source . Thus battery terminal voltage changes with the
load current.

Under no load, i.e. for zero current, . When a load current
flows,
. For a new battery, generally,
is negligible, and it increases as the battery gets
discharged. is a function of electrolyte and terminal materials.

__Non Ideal Current Source:__ See the circuit in figure
3.5.

A non ideal current source is modeled by an internal conductance in
parallel with the source.
.

From the figure, we see that:
. Ideal current
source has , i.e.,
.

__Non-ideal voltage source and current source analysis:__ The source is
non-ideal, hence v is not constant. If it is linear circuit, and are linearly
related. is cause, and is effect. Thus we get:

(3.1) | |||

(3.2) |

This equation is equivalent to fig.3.7. Thus a battery can be represented by 3.8:

Similarly, for a nonideal current source (fig.3.9), if it is linear,

(3.3) | |||

(3.4) |

For ideal current source, always. Thus .

In the above, the sources are modelled using ideal voltage (current) sources whose voltage (current) remains constant.

We can also have *source whose output can be controlled*. These can
be used to model certain real life devices (e.g., transistor) *We
will study transistor later during the course.*