A CD or DVD shows a rainbow pattern because of the __:

Diffraction of the Light
The Diffraction and Diffraction Grating A CD or DVD has closely spaced tracks which work as a diffraction grating to form the familiar rainbow pattern seen when looking at a disk. •Kindly note that diffraction shows that the light propagates as a wave. Diffraction in the atmosphere by small particles can cause a bright ring to be visible around a bright light source like the sun or the moon. •A shadow of a solid object, using light from a compact source, shows small fringes near its edges. The speckle pattern which is observed when laser light falls on an optically rough surface is also a diffraction phenomenon. All these effects are a consequence of the fact that light propagates as a wave. •Diffraction can occur with any kind of wave. Ocean waves diffract around jetties and other obstacles. Sound waves can diffract around objects, which is why one can still hear someone calling even when hiding behind a tree. •It is diffraction which sets the fundamental limit to the resolution of a camera, telescope, or microscope. •Striated muscle is the human body is also works as a natural diffraction grating. It can be used in determining the structure of such muscle.