Dispersion of light

# Dispersion of light ## Dispersion: Definition and demonstration using a prism. Order of colours in the spectrum of white light. Natural occurrence of the dispersion ### Introduction Welcome to our lesson on the fascinating phenomenon of **dispersion of light**! Have you ever wondered why rainbows have so many beautiful colours? Or why white light, when passed through certain objects, separates into a band of colours? Today, we will explore how white light, which seems simple, is actually made up of several different colours, and how we can observe this using a prism and even in nature. ### Key Concepts #### What is Dispersion of Light? Dispersion of light is the phenomenon where **white light splits into its constituent colours** when it passes through a transparent medium, such as a glass prism. This happens because different colours of light travel at slightly different speeds when passing through a medium other than a vacuum. This difference in speed causes each colour to bend (refract) at a slightly different angle. #### Demonstration Using a Prism A **prism** is a transparent optical element with flat, polished surfaces that refract light. When a beam of white light passes through a prism, it undergoes two refractions (once when entering and once when exiting). Because each colour of light has a different wavelength, it experiences a different refractive index in the glass and therefore bends at a slightly different angle. This difference in bending angles causes the colours to spread out, forming a spectrum. * **How it works:** * White light enters one face of the prism. * Each colour (wavelength) bends at a specific angle upon entering the prism. * The light then exits another face of the prism, bending further. * The total effect is that the white light separates into its distinct colours. #### Order of Colours in the Spectrum of White Light The band of colours formed when white light is dispersed is called a **spectrum**. The colours are always arranged in a specific order, which you can remember using the acronym **VIBGYOR**: * **V**iolet * **I**ndigo * **B**lue * **G**reen * **Y**ellow * **O**range * **R**ed **Key points about the order:** * **Violet light** has the shortest wavelength and deviates the most (bends the most) when passing through a prism. * **Red light** has the longest wavelength and deviates the least (bends the least) when passing through a prism. #### Natural Occurrence of Dispersion: The Rainbow One of the most beautiful natural examples of light dispersion is the **rainbow**. * **How rainbows form:** * Rainbows are formed when sunlight (white light) passes through tiny water droplets suspended in the atmosphere after rainfall. * These water droplets act like miniature prisms. * When sunlight enters a water droplet, it undergoes dispersion, splitting into its constituent colours. * The light then undergoes internal reflection inside the droplet. * Finally, the dispersed light refracts again as it exits the droplet, making the different colours visible to an observer. * The colours in a rainbow are always in the order of VIBGYOR, just like in a prism. ### Vocabulary * **Dispersion:** The process by which white light splits into its constituent colours. * **Spectrum:** The band of colours produced when white light is dispersed, e.g., VIBGYOR. * **Prism:** A transparent, typically triangular, block of glass or plastic used to refract and disperse light. * **Refraction:** The bending of light as it passes from one medium (like air) to another (like glass or water). * **Wavelength:** The distance between successive crests of a wave, which determines the colour of light. ### Examples 1. **Rainbows:** The most common and spectacular natural example of dispersion, formed by sunlight passing through water droplets. 2. **Bevelled glass edges:** The edges of thick glass objects, like some tabletops or decorative glass, can sometimes show faint colour separation when light passes through them. 3. **Diamonds:** The sparkling of a diamond is partly due to its ability to disperse white light into its spectrum, creating flashes of colour. ### Exercises 1. Define the term 'dispersion of light'. 2. What is the purpose of a prism in demonstrating the dispersion of white light? 3. List the colours of the visible light spectrum in the correct order, starting from the colour that deviates the least. 4. Which colour of light deviates the most when passing through a prism, and which deviates the least? 5. Briefly explain how a rainbow is formed. ### Assignment 1. Draw a neat, labelled diagram showing the dispersion of white light through a glass prism. Clearly indicate the incident white light, the prism, the refracted rays, and the resulting spectrum of colours. 2. Explain why different colours of light refract at different angles when they pass through a transparent medium like a prism. ### Summary In this lesson, we've learned that white light is not a single colour but a combination of many. The phenomenon of **dispersion** is the splitting of this white light into its individual colours when it passes through a transparent medium like a **prism**. The resulting band of colours is called a **spectrum**, with colours arranged in the order **VIBGYOR** (Violet, Indigo, Blue, Green, Yellow, Orange, Red). Violet light deviates the most, and red light deviates the least. A beautiful natural example of dispersion is the formation of a **rainbow**, where water droplets act as tiny prisms to split sunlight into its vibrant colours.