What happens during destructive interference of light waves?

During destructive interference of light waves, the waves combine to form a resultant wave of lower or zero amplitude.

Destructive interference is a fundamental concept in wave physics, including light which is an electromagnetic wave. It occurs when two or more waves meet and combine in such a way that they cancel each other out, resulting in a wave of lower amplitude or even zero amplitude. This is in contrast to constructive interference, where waves combine to form a wave of greater amplitude.

The principle of superposition is key to understanding destructive interference. According to this principle, when two or more waves meet at a point, the resultant wave at that point is the algebraic sum of the amplitudes of the individual waves. If the waves are in phase (i.e., their peaks and troughs align), they will interfere constructively, resulting in a wave of greater amplitude. However, if the waves are out of phase (i.e., the peak of one wave aligns with the trough of another), they will interfere destructively, resulting in a wave of lower amplitude.

In the context of light waves, destructive interference can result in dark bands or 'fringes' in an interference pattern. This is because light waves are transverse waves, meaning their oscillations are perpendicular to the direction of energy transfer. When two light waves interfere destructively, their electric fields cancel each other out, resulting in no light (a dark fringe). This phenomenon can be observed in various optical experiments, such as Young's double-slit experiment.

The conditions for destructive interference depend on the wavelength of the light and the path difference between the interfering waves. For two waves of the same wavelength, destructive interference occurs when the path difference is an odd multiple of half the wavelength. This is because this path difference causes the waves to be 180 degrees out of phase, resulting in complete cancellation.

In conclusion, destructive interference of light waves is a fascinating phenomenon that demonstrates the wave nature of light. It is a key concept in the study of optics and wave physics, with important implications for technologies such as lasers and optical fibres.