Electronics: Definition, ldeal Constant - voltage Source and Ideal Constant- current Source

What is electronics ? 

Electronics is a branch of physics which deals with the study of the emission, flow and control of electrons in matter or in a vacuum. It comprises physics,engineering, technology and applications. Analog electronics is an electronic system which operates on continuously varying signals. Digial electronics is an electronic system which operates on digital signals. Digital electronic ciruits are usually made from large assemblies of logic gates and integrated circuits (ICs).

Ideal Constant-voltage Source

A voltage source with very low internal resistance is called a constant-voltage source. The output voltage remains essentially the same when the load current changes. If the internal resistance of such a voltage source is zero, the source is called an ideal constant-voltage source.

Suppose a battery of emf 6 V and internal resistance = 0.005 ohm is connected to a variable load RL. If the load current increases from 1 A to 100 A, the potential difference across the internal resistance will be from 0.005 V to 0.5 V and the output voltage will be from 5.995 V to 5.5V. This means that the output voltage remains almost constant over a wide variation in the load current from 1 A to 100 A while the corresponding load resistance varies from 5.995 ohm to 0.055 ohm. Therefore when the load resistance is 5.995 ohm its output voltage across it is VL =1 x 5.995 = 5.995 V and when the load resistance is 0.055 ohm, its output voltage across it is VL=100 x 0.055=5.5 V.

Ideal Constant-current Source

A voltage source with very high internal resistance compared with external load resistance is called a constant-current source. The output current remains essentially the same when the output voltage varies. If the internal resistance of such a voltage source is infinity, the source is called an ideal constant-current source.

Suppose a battery of emf 6 V and internal resistance r = 1M ohm is connected to a variable load RL. If the load current increases from 20 kohm(0.02Mohm) to 200 k ohm(0.2 Mohm), the current in the load resistance will vary from 6 V/1.02 M ohm = 5.9micro ohm to 6V / 1.2  M ohm= 5micro A This means that when the load resistance increases 10 times, the current decreases by 0.9 μA. Therefore the source can be considered to be a constant-current source.