Demonstrate dispersion of light after passing a white light through a prism.
Show Hint
To get a sharp and clear spectrum, it is crucial to use a narrow beam of white light. If the beam is too wide, the colors will overlap, and the spectrum will be blurry. Using a ray box with a slit is the best way to achieve this.
Step 1: Understanding the Concept:
Dispersion is the phenomenon of splitting of white light into its constituent colors when it passes through a transparent medium like a glass prism. This happens because the refractive index of the prism material is different for different wavelengths (colors) of light. According to Cauchy's relation, the refractive index is greater for shorter wavelengths (like violet) and smaller for longer wavelengths (like red). Therefore, violet light bends the most, and red light bends the least, separating the colors into a spectrum. Step 2: Apparatus Required:
- A glass prism.
- A source of white light (a ray box with a narrow slit is ideal, but sunlight from a window or a torch can also be used).
- A white screen. Step 3: Ray Diagram and Procedure: Ray Diagram:Procedure:
1. Setup: Perform the experiment in a dark room for the best visibility. Place the prism on a table.
2. Directing Light: Arrange the source of white light so that a narrow beam of light is incident on one of the refracting faces of the prism.
3. Positioning the Screen: Place a white screen on the other side of the prism, where the light emerges.
4. Observation: Adjust the angle of the incident beam and the position of the screen until a clear band of colors is observed on the screen. This band of colors is called a spectrum.
5. Identifying Colors: Observe the colors in the spectrum. You will see a continuous band starting from Red at the top (least deviated) and ending with Violet at the bottom (most deviated). The order of colors is Violet, Indigo, Blue, Green, Yellow, Orange, Red (VIBGYOR). Step 4: Conclusion:
The experiment demonstrates that white light is a mixture of several colors. When it passes through a prism, the different colors travel at different speeds and are refracted at slightly different angles, causing them to separate and form a spectrum. This phenomenon is called dispersion.
