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An active device can have power gain. A passive device can not. Passive devices, however can have voltage (or) current gain. For example, consider a seriels L-C circuit that is excited at its resonant frequency. The inductor and capacitor are passive components. The voltage across the inductor can be greater than the excitation voltage. Similarly, the voltage across the capacitor can be greater than the excitation voltage. Theroretically, for ideal (infinite Q) components, the voltage across each component would be infinite, and the current through each component would be infinite! However, the power dissipated by the components would be zero, because the voltage and current would be 90 deg out of phase. (Power = VICos(Theta)).
Active devices are those which are capable of changing the properties of signal which is applied(viz. amplification,attenuation etc..) .also they can have -ve resistance..
Passive device cant change the properties of a signal which is applied to it..Also they cant ve -ve resi.
Active device is the device which can contribute power examples like bjt, mosfet etc
Passive devices may be device which may consume energy . there rms value of genearation of energy may be zero. examples like resistors, capactiores etc
Active devices are energy controllers, sometimes converting one form of energy to another: chemical, hydraulic, thermal energy, mechanical , nuclear, solar, etc, into electrical energy, driving electrical current around the circuit and hence delivering continuous energy to it.
According to one definition, an active device is a source of electric power in a circuit, such as batteries and generators. Another definition refers to electronic switching devices such as transistors