The correct option is (a).
Explanation
Dispersion of light is the phenomenon of splitting of a beam of white light into its constituent colors when it passes through a transparent medium like a glass prism. This occurs because different colors of light travel at different speeds in the medium, leading to different angles of deviation.
Statement-wise Analysis
- Statement 1 is Correct: When a beam of sunlight (white light) passes through a glass prism, it splits into a spectrum of seven colors: Violet, Indigo, Blue, Green, Yellow, Orange, and Red (VIBGYOR). This process is known as dispersion.
- Statement 2 is Incorrect: The phenomenon of dispersion demonstrates that white light is composite in nature, meaning it consists of a mixture of different colors (wavelengths), not a single color. Isaac Newton proved this by using a second prism to recombine the spectrum back into white light.
- Statement 3 is Incorrect: Rainbows are formed by the dispersion, refraction, and total internal reflection of sunlight by spherical water droplets in the atmosphere. While "moonbows" (lunar rainbows) exist, they are rare; the general phenomenon of a rainbow is caused by sunlight, not the reflection of light from the moon. Furthermore, the primary mechanism involves dispersion and refraction within the droplet, not merely reflection from an external body.
Key Takeaway: Dispersion is the splitting of white light into its constituent spectrum (VIBGYOR) due to wavelength-dependent refractive indices. A rainbow is a natural example of dispersion caused by atmospheric water droplets.