What is meant by resonance in relation to waves?

Resonance is a phenomenon that occurs when a system is subjected to an external force that matches its natural frequency. When this happens, the system responds with an increased amplitude of oscillation. This means that rather than a typical response to an applied force, the system undergoes much greater oscillations because of the efficient transfer of energy from the driving force into the system itself.

For instance, if you push a swing at just the right moment—when it is at its natural frequency—you will see the swing go higher than if you pushed it at random intervals. This principle is crucial in various applications, including musical instruments, bridges, and even buildings, where ensuring that natural frequencies do not coincide with external forces (such as winds or seismic activity) is vital for stability.

In this context, the other options illustrate different concepts that do not encapsulate the essence of resonance. The first choice mistakenly suggests a combination of frequencies rather than a single natural frequency. The third option refers to destructive interference, which involves cancellation of waves but does not characterize resonance. Lastly, the fourth choice describes the transfer of sound between mediums, which is not specific to resonance either, as resonance is fundamentally about the amplification of oscillations at a specific frequency, not merely about acoustic transmission