Newton's Disc
Explanation
White light is a composite of seven visible colors (Violet, Indigo, Blue, Green, Yellow, Orange, Red). While dispersion is the separation of white light into these colors, the reverse process involves combining them to perceive white light. This can be demonstrated physically or optically using the physiological phenomenon of persistence of vision.
Option Analysis
- Prism is incorrect: A Prism is primarily used to disperse white light into its constituent spectrum (dispersion). While two prisms arranged in an inverted manner can recombine the spectrum, a single prism acts as a dispersing element.
- Newton's Disc is correct: Newton's Disc is a circular disc divided into sectors painted with the seven colors of the visible spectrum in specific proportions. When the disc is rotated rapidly, the human eye cannot distinguish the individual colors due to the persistence of vision (the retention of a visual impression for about 1/16th of a second). Consequently, the colors overlap on the retina, and the brain perceives the combined effect as white light.
- Kaleidoscope is incorrect: A Kaleidoscope is an optical instrument containing mirrors inclined at specific angles. It operates on the principle of multiple reflections to create symmetrical, changing patterns, not to recombine light spectra.
- Periscope is incorrect: A Periscope is an optical device used to view objects that are not in the direct line of sight (e.g., over an obstacle or from a submarine). It utilizes mirrors or prisms to reflect light, typically based on the laws of reflection.
Key Takeaway
Newton's Disc demonstrates the composition of white light by utilizing the persistence of vision to optically mix the seven spectral colors into white when rotated at high speed.