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Chapter 4. Linear Circuits > Power and Root Mean Square Values

Power and Root Mean Square Values
Using a linear voltage amplifier on a feeble signal will result in an output that is a signal at a much higher voltage level, but we cannot necessarily use this signal to operate devices such as a loudspeaker or an electric motor. The reason is that these devices need a substantial amount of current passed through them as well as the voltage across their terminals, and a voltage amplifier cannot supply large currents. What we need is a power amplifier.
For example, a voltage amplifier might provide an output that was a voltage wave of 6 V which could supply no more than 1 mA of current. The power amplifier might provide a wave with a voltage of 6 V and a current of 2 A.

Note
The name of power amplifier is misleading, because any amplification of voltage (without reducing current) or current (without reducing voltage) is power amplification. In fact, the power amplifier is usually a current amplifier, but since it is used to supply power to devices like loudspeakers, the name of power amplifier is more common.

  

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