risonanza

Risonanza is the phenomenon by which a system responds with amplified oscillations when driven at a frequency that matches one of its natural modes. The term, Italian for resonance, is used across physics, engineering, chemistry and medicine. In general, resonance arises when energy transfer into the system is most efficient, so small inputs produce large outputs. It can be exact (driving frequency equals a natural frequency) or near-resonant (close to a natural frequency with finite damping).

In mechanical and acoustical contexts, every object or structure has characteristic natural frequencies determined by mass, stiffness, and boundary conditions. When excited near these frequencies, the amplitude of motion increases. This is heard in musical instruments, observed in vibrating machines, and is a critical factor in the design of bridges and buildings, where damping limits excessive oscillations.

In electrical engineering, resonant phenomena occur in circuits containing inductors and capacitors. A series or parallel LC circuit has a resonance frequency f0 = 1/(2π√(LC)). At resonance, impedance is minimized in a series circuit and maximized in a parallel one, allowing selective filtering and frequency selection. The quality factor Q measures the sharpness of the resonance.

In quantum and optical contexts, resonances describe enhanced responses at certain energies or frequencies, such as atomic or molecular transitions, optical cavities, or scattering resonances with finite lifetimes, described by resonance widths.

In chemistry, resonance also denotes the delocalization of electrons within a molecule, illustrated by alternative contributing structures; this use is distinct from dynamic vibrational resonance but relates to stability.

In Italian, risonanza is commonly used in phrases like risonanza magnetica (magnetic resonance imaging).