ByAPSEEE

A voltage source is a source of energy which establishes a potential difference across its terminals. Most of the sources encountered in everyday life are voltage sources, e.g. batteries, d.c. generators, alternators, etc. The current source is a source of energy that provides a current e.g., collector circuits of transistors. Voltage and current sources are called active elements because they provide electrical energy to a circuit.

**Ideal voltage Source**

An ideal voltage source is one which maintains a constant terminal voltage, no matter how much current is drawn from it. An ideal voltage source has zero internal resistance.

**Practical Voltage Source**

A practical voltage source has very low internal resistance, that causes its terminal voltage to decrease when load current is increased and vice-versa.

**Ideal Current Source**

An ideal current source is one which maintains will supply the same current to any resistance connected across its terminals. An ideal current source has infinite internal resistance.

**Practical Current Source**

A practical current source has very high internal resistance. Therefore, the load current will change as the value of load resistance changes.

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