The persistence of vision.
Explanation
The Newton’s Disc, a classic experiment used to demonstrate that white light is composed of the seven constituent colours of the visible spectrum. While the disc physically contains separate colours, the mechanism that causes it to appear white during rotation is physiological rather than purely physical.
Analysis of the Phenomenon
- Persistence of Vision: The human eye retains an impression of an image on the retina for approximately 1/16th of a second. When the disc rotates rapidly, the eye receives the sensation of the different colours in quick succession. Before the impression of one colour fades, the impression of the next colour is formed. Consequently, the brain blends these overlapping impressions, resulting in the perception of white light.
- Dispersion (Incorrect): Dispersion is the phenomenon of splitting white light into its constituent colours (e.g., through a prism). The rotating disc illustrates the reverse concept-recombining colours-but the visual effect is due to the eye's retention of images, not the physical splitting of light.
- Scattering and Total Internal Reflection (Incorrect): Scattering involves the deviation of light by particles, and Total Internal Reflection involves the reflection of light within a denser medium. Neither process is involved in the colour mixing observed in Newton's Disc.
Key Takeaway
A rapidly rotating multi-coloured disc appears white due to the persistence of vision, which limits the eye's ability to resolve fast-moving individual colours, causing them to blend into a composite white image.