Question 20: Draw a ray diagram showing the dispersion through a prism when a narrow beam of white light is incident on one of its refracting surfaces. Also indicate the order of the colours of the spectrum obtained.
Answer:
Diagram:
The prism splits the incident white light into the band of colours. The dispersion of white light is shown by one activity- take a thick sheet of cardboard and make a small hole in it in its middle. Now allow the sunlight to fall on this slit or hole which gives a narrow beam of white light. Take a glass prism and allow the light from the hole to fall on one of its faces. Now turn the prism slowly until the light comes out of the nearest screen. We will observe the different colour bands. The various colours are seen- violet, Indigo, blue, green, yellow, orange and red and the sequence will be the same as written.
The acronym is VIBGYOR so that we remember the sequence of colours and the band of coloured components of the light beam is known as spectrum and the splitting of light into its components colours is known as dispersion.
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