What is Spectrum Formation by Prism?

S6-SA3-0349

Grade Level:

Class 10

AI/ML, Physics, Biotechnology, Space Technology, Chemistry, Engineering, Medicine

Definition

What is it?

Spectrum formation by a prism is the splitting of white light into its constituent seven colours (VIBGYOR - Violet, Indigo, Blue, Green, Yellow, Orange, Red) when it passes through a transparent triangular prism. This happens because each colour of light bends at a slightly different angle inside the prism.

Simple Example

Quick Example

Imagine you have a single white LED torch, and you shine its light through a special glass piece (a prism) onto a white wall. Instead of seeing just a white spot, you'll see a beautiful band of colours, just like a rainbow! This colourful band is the spectrum formed by the prism.

Worked Example

Step-by-Step

Let's understand how different colours bend differently:
1. White light, which is a mix of all colours, enters the prism.
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2. As it enters, the light bends (refracts) towards the base of the prism. This bending is called 'deviation'.
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3. Inside the prism, different colours travel at slightly different speeds. Violet light travels slowest and bends the most.
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4. Red light travels fastest and bends the least.
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5. When the light exits the prism, it bends again, further separating the colours.
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6. Because violet light deviates the most and red light deviates the least, they spread out, forming a band of colours from violet to red.
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7. This spread-out band of colours is the spectrum. Answer: White light splits into VIBGYOR due to different bending angles for each colour.

Why It Matters

Understanding spectrum formation is crucial in fields like space technology, where scientists use spectrographs to analyse light from stars and planets, telling us what they are made of. In medicine, spectroscopy helps diagnose diseases by analysing light absorbed or emitted by substances. This knowledge is key for careers in research, optics engineering, and astronomy.

Common Mistakes

MISTAKE: Thinking the prism adds colour to the white light. | CORRECTION: The prism only separates the colours that are already present in the white light; it doesn't create new colours.

MISTAKE: Believing all colours bend by the same amount inside the prism. | CORRECTION: Different colours (wavelengths) of light travel at different speeds in glass, causing them to bend (deviate) by different amounts. Violet bends most, Red bends least.

MISTAKE: Confusing reflection with refraction in this context. | CORRECTION: Spectrum formation is due to refraction (bending of light as it passes from one medium to another), not reflection (bouncing back of light).

Practice Questions

Try It Yourself

QUESTION: Which colour of light deviates the most when passing through a prism? | ANSWER: Violet light

QUESTION: Why does white light split into different colours when passing through a prism? | ANSWER: White light splits because different colours (wavelengths) travel at different speeds inside the prism, causing them to refract or bend by different amounts.

QUESTION: If you shine a pure red light through a prism, what will you observe on a screen? Explain why. | ANSWER: You will observe only red light on the screen. This is because pure red light consists of only one colour, so there are no other colours to split into a spectrum.

MCQ

Quick Quiz

What is the phenomenon called when white light splits into its constituent colours after passing through a prism?

Reflection

Refraction

Dispersion

Scattering

The Correct Answer Is:

The splitting of white light into its constituent colours is specifically called dispersion. While refraction is the bending of light, dispersion is the phenomenon where different colours refract by different amounts, leading to separation.

Real World Connection

In the Real World

You see spectrum formation every day, though perhaps not with a prism! Rainbows are natural examples of spectrum formation where tiny water droplets act like prisms, splitting sunlight into VIBGYOR after a rain shower. Scientists at ISRO use similar principles with advanced instruments to study light from distant stars, helping them understand what elements are present in space.

Key Vocabulary

Key Terms

DISPERSION: The phenomenon of splitting white light into its constituent colours.| REFRACTION: The bending of light as it passes from one medium to another.| SPECTRUM: The band of seven colours (VIBGYOR) formed when white light is dispersed.| PRISM: A transparent optical element with flat, polished surfaces that refract light.

What's Next

What to Learn Next

Now that you understand how a prism forms a spectrum, you can explore 'Why the Sky Appears Blue' or 'Formation of a Rainbow'. These concepts build on the idea of light dispersion and refraction, showing you more amazing phenomena around us!