PhysicsThe human eye and the colourful worldClass 10Class 12

Prism refraction, dispersion & rainbow: interactive simulation

When a beam of white light passes through a glass prism, it splits into a band of seven colors: Violet, Indigo, Blue, Green, Yellow, Orange, Red (VIBGYOR). This phenomenon is called dispersion.

Useful for: CBSE Boards, NEET, JEE Main

Try this

Dispersion occurs because glass has different refractive indices for different wavelengths: violet light bends the most (shortest wavelength), while red light bends the least. In a primary rainbow, sunlight undergoes refraction, dispersion, and total internal reflection within spherical raindrops.

  1. 1

    Drag the "Angle of Incidence" slider to find Minimum Deviation.

    What you should see

    Around i ≈ 48°–49°, angle of incidence equals angle of emergence (i = e), the ray inside the prism passes parallel to the base, and deviation δ reaches its minimum value.

  2. 2

    Switch to "Rainbow in Raindrop" mode.

    What you should see

    Sunlight refracts at the front surface, reflects internally (TIR) at the back, and refracts out: Red emerges at 42° and Violet at 40° into the observer’s eye.

Formulas behind it

Prism Formula (Minimum Deviation)

μ=sin⁡(A+δm2)sin⁡(A2)\mu = \frac{\sin\left(\frac{A + \delta_m}{2}\right)}{\sin\left(\frac{A}{2}\right)}

Angle of Deviation

δ=i+e−A\delta = i + e - A

Cauchy’s Dispersion Formula

μ(λ)=A+Bλ2\mu(\lambda) = A + \frac{B}{\lambda^2}

Common mistakes

  • Thinking red light bends the most. Red bends the LEAST because it has the longest wavelength and lowest refractive index in glass.
  • Assuming total internal reflection alone forms a rainbow. A rainbow requires refraction, dispersion, AND total internal reflection.
Stuck on a prism refraction, dispersion & rainbow question?Snap it and get a whiteboard video solution.

FAQ

Why does white light disperse into spectrum colors in a prism but not in a glass slab?

In a rectangular glass slab, the opposing refracting faces are parallel, so emergent rays for all colors emerge parallel to each other. In a prism, the non-parallel faces cause emergent rays to diverge at different angles.

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