Which of the following devices can be classified as an energy source?

An amplifier is classified as an energy source because it takes a small input signal and increases it to a level sufficiently large to drive a load, such as speakers. Amplifiers function by drawing power from a power supply and converting that electrical energy into a larger signal output. This makes them essential components in many audio and communication systems where signal enhancement is necessary.

The other devices listed, such as a resistor, copper wire, and speaker, do not create or supply energy in the same way. A resistor is primarily used to resist the flow of current, converting electrical energy into heat rather than acting as a source. Copper wire serves as a conductor, facilitating the flow of electricity but does not generate energy. A speaker, while it converts electrical energy into sound energy, relies on an external amplifier to provide the necessary energy to produce sound. Thus, the amplifier stands out as the device that actively sources energy for further use in a circuit.