PhysicsRay opticsClass 10Class 12

Refraction and total internal reflection: interactive simulation

Light changes speed when it enters a new medium, and that change of speed bends its path. Going into a denser medium it bends towards the normal; coming out it bends away.

Useful for: JEE Main, NEET, CBSE Boards

Try this

Drag to aim the ray. When light goes from a denser to a rarer medium and the angle is larger than the critical angle, no light gets through at all — it is totally reflected. That is how optical fibres and the sparkle of diamonds work.

  1. 1

    Send light from glass (1.5) into air at 35°.

    What you should see

    It bends away from the normal to about 59.4°.

  2. 2

    Increase the angle slowly in glass → air.

    What you should see

    At about 41.8° the refracted ray skims the surface; beyond it there is total internal reflection.

  3. 3

    Compare the critical angles of water and diamond.

    What you should see

    Water ≈ 48.8°, diamond ≈ 24.4°. Diamond traps light much more easily, which is why it sparkles.

  4. 4

    Send light from air into glass at 35°.

    What you should see

    It bends towards the normal to about 22.5°, and TIR never happens in this direction.

Formulas behind it

Snell’s law

n1sin⁡i=n2sin⁡rn_1 \sin i = n_2 \sin r

Refractive index

n=cvn = \frac{c}{v}

Critical angle (n₁ > n₂)

sin⁡C=n2n1\sin C = \frac{n_2}{n_1}

Common mistakes

  • Expecting total internal reflection when light goes from a rarer to a denser medium.
  • Measuring angles from the surface instead of from the normal.
  • Forgetting that the frequency does not change on refraction — only speed and wavelength do.
Practise 295 questionsCheck your answer instantly, with a worked solution.Ray Optics chapter guideFormula sheet, solved examples and PYQ patterns.Stuck on a refraction and total internal reflection question?Snap it and get a whiteboard video solution.

FAQ

Why does a pool look shallower than it is?

Light from the bottom bends away from the normal as it leaves the water, so it seems to come from a raised point. Apparent depth = real depth / n.

Does light bend if it hits the surface along the normal?

No. At i = 0 the ray goes straight through, although its speed still changes.

What is an optical fibre?

A thin glass core surrounded by a cladding of lower refractive index. Light hits the boundary above the critical angle and is totally reflected again and again along the fibre.

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