*There are two kinds of electronic amplifiers: voltage amplifiers and power amplifiers. A basic understanding of power and its relation to voltage, current and resistance is useful to appreciate the distinctions between the two classes. Ohm’s laws establish the relationship between voltage, current and resistance, E = IR, where the voltage (E) equals the current (I) multiplied by the resistance. If the resistance remains constant and the voltage increases, there will be a corresponding increase in current. This is the mode of operation of a voltage amplifier. When the voltage is kept constant and the current is increased, there is a corresponding decrease in resistance. This is the operation mode of a power amplifier. The power is defined by the law of Watt as P = I V, where the power (P) is equivalent to the current (I) multiplied by the voltage (V). When the voltage remains constant and the current increases, the power also increases.*

*There are two kinds of electronic amplifiers: voltage amplifiers and power amplifiers. A basic understanding of power and its relation to voltage, current and resistance is useful to appreciate the distinctions between the two classes. Ohm’s laws establish the relationship between voltage, current and resistance, E = IR, where the voltage (E) equals the current (I) multiplied by the resistance. If the resistance remains constant and the voltage increases, there will be a corresponding increase in current. This is the mode of operation of a voltage amplifier. When the voltage is kept constant and the current is increased, there is a corresponding decrease in resistance. This is the operation mode of a power amplifier. The power is defined by the law of Watt as P = I V, where the power (P) is equivalent to the current (I) multiplied by the voltage (V). When the voltage remains constant and the current increases, the power also increases.*

### Voltage

A power amplifier can cause a slight decrease in the voltage signal, but regularly keeps it relatively constant. A voltage amplifier significantly increases the amount of the voltage signal.

### Current

A power amplifier again increases the current signal, while the voltage amplifier causes a slight increase in the amount of the current signal.

### Resistance

A power amplifier causes a significant decrease in the output resistance of the circuit. A voltage amplifier keeps the resistance high in the circuit. In a voltage amplifier, the resistance of the circuit may vary slightly, either up or down.

### Power

A power amplifier significantly increases the power signal. A voltage amplifier can cause a slight increase in the amount of the power signal.

References

- All About Circuits: an analogy for Ohm’s law
- Integrated Publishing: introduction to amplifiers
- Power Law: the ratio of voltage, current and watts