Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Dispersion of Light: It is the phenomenon of splitting of a beam of white light into its seven constituent colors when passed through a transparent medium like a glass prism.
Spectrum: The band of seven colors obtained on a screen when white light passes through a prism is called a spectrum. The colors follow the acronym VIBGYOR (Violet, Indigo, Blue, Green, Yellow, Orange, Red).
Reason for Dispersion: Different colors of light have different wavelengths and travel at different speeds in a medium. Violet light deviates the most (shortest wavelength), while Red light deviates the least (longest wavelength).
Rainbow Formation: A rainbow is a natural spectrum appearing in the sky after rain. It is caused by the dispersion of sunlight by tiny water droplets present in the atmosphere.
Mechanism of Rainbow: Each water droplet acts like a small prism. When sunlight enters a droplet, it first undergoes refraction and dispersion, then internal reflection, and finally refraction again as it leaves the droplet.
Observer Position: To see a rainbow, the Sun must be behind the observer and the water droplets (rain) must be in front of the observer.
📐Formulae
💡Examples
Problem 1:
During the formation of a rainbow, which optical phenomena occur inside a water droplet? List them in order.
Solution:
- Refraction, 2. Dispersion, 3. Internal Reflection, 4. Refraction.
Explanation:
As sunlight enters the raindrop, it slows down and bends (refraction), splitting into colors (dispersion). It then hits the back of the drop and reflects (internal reflection) before exiting and bending again (refraction).
Problem 2:
If a beam of white light passes through a glass prism, which color will be found at the bottom of the spectrum (furthest from the original path)?
Solution:
Violet light.
Explanation:
Violet light has a shorter wavelength and travels slower in glass compared to Red light. According to the principles of refraction, light that slows down more deviates more. Therefore, Violet undergoes the maximum deviation and appears at the bottom of the VIBGYOR stack.
Problem 3:
Calculate the speed of light in a glass prism if its refractive index . (Assume )
Solution:
Explanation:
Using the formula , we can rearrange it to find the speed of light in the medium by dividing the speed of light in vacuum by the refractive index.