Skip to content
Light & Optics · Physics

Prism: Minimum Deviation and Dispersion Simulation

Trace a ray through a glass prism, record the deviation at each angle of incidence and plot the i–δ graph. Find the minimum, then split white light into a spectrum.

Interactive virtual lab · no download · works on phones and laptops

Chapter
Ray Optics and Optical Instruments
For
Class 12 · JEE · NEET
Time
~15 min

How to use it

  1. 1Set the prism angle, material and angle of incidence.
  2. 2Press Record reading at several angles.
  3. 3Go to the minimum and read n from your table.
  4. 4Dispersion tab: compare crown and flint glass.

What to notice

  • δ = i + e − A, and it has a minimum where i = e.
  • At minimum deviation r₁ = r₂ = A/2 and n = sin((A + δm)/2)/sin(A/2).
  • Violet deviates more than red because n falls with wavelength.
  • Flint glass disperses more than crown glass.

For teachers

Teach it in 21 minutes

A lesson plan, questions to put to the class, a quick quiz you can project or print, and the formulas behind Prism: Minimum Deviation and Dispersion.

  1. 1Hook

    ~2 min
    • Ask: “A glass window doesn't make a rainbow, so why does a prism?” Collect two or three answers, then shine white light through the prism.

  2. 2Demonstrate

    ~9 min
    • Set the prism angle, material and angle of incidence.
    • Press Record reading at several angles.
    • Go to the minimum and read n from your table.
    • Dispersion tab: compare crown and flint glass.

  3. 3Pause and ask

    ~5 min
    • Have a student say this in their own words: δ = i + e − A, and it has a minimum where i = e.
    • Have a student say this in their own words: At minimum deviation r₁ = r₂ = A/2 and n = sin((A + δm)/2)/sin(A/2).
    • Have a student say this in their own words: Violet deviates more than red because n falls with wavelength.
    • Have a student say this in their own words: Flint glass disperses more than crown glass.

  4. 4Check

    ~5 min
    • Run the 5-question quiz below: project it and take answers by show of fingers (1–4), or print it as a worksheet.

About the Prism: Minimum Deviation and Dispersion simulation

A ray passing through a triangular glass prism is bent at both faces and comes out deviated towards the base. The deviation δ = i + e − A depends on the angle of incidence: it falls, reaches a minimum when the ray passes through symmetrically, then rises again. Measuring that minimum is the standard laboratory way to find the refractive index of a prism.

This prism simulation lets you record (i, e, δ) readings into a table, plots the i–δ graph, and computes n from your minimum. A second tab sends white light through crown or flint glass and splits it into a spectrum, giving the deviation of each colour, the angular dispersion and the dispersive power.

Also covers: angle of minimum deviation, i-delta graph, refractive index of prism, dispersion, dispersive power, prism experiment.

Frequently asked questions

What is the condition for minimum deviation in a prism?

The ray passes symmetrically: i = e and r₁ = r₂ = A/2. Inside the prism it travels parallel to the base (for an isosceles prism).

How do you find the refractive index from the angle of minimum deviation?

n = sin((A + δm)/2)/sin(A/2). For A = 60° and δm = 37.2°, n = 1.50.

Why does a prism split white light?

The refractive index of glass is larger for violet than for red, so violet is deviated more: the colours separate.

Try next

All simulations