Correct Option: (D)
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Refraction: When sunlight encounters the transparent polycarbonate layer of the compact disc, it undergoes refraction. This involves the bending of light as it passes from air into the plastic medium and then back out. While the primary spectral separation is due to diffraction, refraction is a fundamental process for light to interact with the internal structure of the CD.
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Diffraction: The surface of a CD contains a spiral track of microscopic pits and lands, which are closely spaced. These act as a diffraction grating. When light strikes this periodic structure, it is diffracted. Different wavelengths (colours) of light are diffracted at different angles, leading to the separation of white light into its constituent colours, producing the rainbow-like effect.
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Transmission: For light to interact with the internal reflective layer and the diffraction grating structure, it must transmit through the outer transparent protective layers of the CD. This transmission allows the light to reach the data-carrying surface and then exit after undergoing reflection and diffraction.
These three optical phenomena collectively contribute to the observation of rainbow-like colours on a CD when viewed in sunlight.
Incorrect Options:
Options (1) reflection and diffraction, (2) reflection and transmission, and (3) diffraction and transmission are incomplete. The phenomenon observed on a CD involves the combined effects of refraction (as light enters and exits the transparent layers), diffraction (due to the microscopic tracks acting as a grating, which disperses light into its colours), and transmission (for light to pass through the layers and interact with the reflective surface). Omitting any of these crucial aspects provides an incomplete explanation for the observed rainbow-like colours. While reflection occurs from the metallic layer, the primary mechanisms for the dispersion of light into colours are refraction and diffraction, enabled by transmission.