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Semiconductor Electronic: Material, Devices And Simple Circuits — Physics STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 SciencePhysicsSemiconductor Electronic: Material, Devices And Simple Circuits5 Marks
Question
In a CE transistor amplifier there is a current and voltage gain associated with the circuit. In other words there is a power gain. Considering power a measure of energy, does the circuit voilate conservation of energy?
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Answer

Key concept: Different gain in CE transistor amplifier:
  1. Ac current gain: $\beta_\text{ac}=\Big(\frac{\Delta\text{i}_\text{c}}{\Delta\text{i}_\text{b}}\Big)\text{V}_\text{CE}=\text{constant}$
  2. dc current gain: $\beta_\text{dc}=\frac{\text{i}_\text{c}}{\text{i}_\text{b}}$
  3. Voltage gain: $\text{A}_\text{v}=\frac{\Delta\text{V}_0}{\Delta\text{V}_\text{i}}=\beta_\text{ac}\times\text{Resistance gain}$
  4. Power gain: $=\frac{\Delta\text{P}_0}{\Delta\text{P}_\text{i}}=\beta_\text{ac}^2\times\text{Resistance gain}$
The power gain is very high in CE transistor amplifier. In this circuit, the extra power required for amplified output is obtained from DC source. Thus, the circuit used does not violate the law of conservation.

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