When light waves interact with a metal surface, the incident light can cause the free electrons in the metal to oscillate. These oscillating electrons then emit secondary waves, which are known as scattered or reflected waves. The key to understanding why the reflected waves do not cancel out with the incident light outside the metal lies in considering the nature of the scattering process and the overall wave propagation.
The oscillating electrons in the metal act as tiny radiating sources that generate electromagnetic waves. However, the secondary waves produced by these electrons do not cancel out the incident light because of several reasons:
Amplitude: The oscillating electrons emit secondary waves with an amplitude proportional to their displacement. While the emitted waves are out of phase with the incident waves, their amplitude is much smaller compared to the incident light's amplitude. Therefore, the reflected waves have a significantly lower intensity than the incident light, and their contribution to the total wave amplitude is relatively minor.
Phase Distribution: The scattered waves have a random phase distribution due to the complex interactions of the incident light with multiple electrons in the metal. This randomization of phase causes the reflected waves to be scattered in various directions, resulting in a diffused reflection. Consequently, the scattered waves do not align perfectly to cancel out the incident light in any particular direction.
Interference: The interaction of the incident light with the oscillating electrons does lead to interference between the incident and reflected waves. However, this interference does not result in complete cancellation but rather modifies the amplitude and phase of the resulting wave. The specific interference pattern depends on the geometry of the scattering process and the properties of the metal surface, leading to phenomena such as specular reflection or diffuse reflection.
In the case of specular reflection, where the metal surface is smooth and the incident light is reflected in a well-defined direction, the interference between the incident and reflected waves results in constructive and destructive interference in different regions. This interference pattern determines the reflected wave's intensity and phase, which are not sufficient to cancel out the incident light completely.
In summary, while the oscillating electrons in a metal produce waves out of phase with the incident light, the amplitude, phase distribution, and interference effects prevent the reflected waves from fully canceling out the incident light. Instead, the reflected waves contribute to the overall wave pattern, resulting in phenomena like reflection and diffraction.