• Pixel-art sticker of Slowax, personifying Refractive Index, with the caption “Light Slows In Glass.”

IndexForces & FieldsSticker

Slowax

Refractive Index Physics

\[n = \frac{c}{v}\]
$4.99 USD
$4.99 USD
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Flat $6 shipping worldwideMade to order, ships in 2–5 business days

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Size3″ × 3″

3″ × 3″ kiss-cut sticker.

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Flat $6 shipping on every order, worldwide, whatever's in it.

Delivery times & where we ship

Returns & replacements21 days

Every item is printed to order, so we can’t accept returns or exchanges for change of mind, or if you ordered the wrong size or colour.

Print defect, misprint, damage or the wrong item? We’ll send a free replacement, or a refund if you prefer. Report it within 21 days of delivery with a photo; no need to send it back.

Full refund & replacement policy

The physics

Meet Slowax, a beam of light who slows down as she enters a block of glass.

Light travels at c = 299 792 458 m/s in a vacuum, but more slowly in materials. The refractive index n is the ratio of the speed in vacuum to the speed in the material, so it is always at least 1.

Water has n ≈ 1.33, so light in water travels at about 3.00 × 10⁸ / 1.33 ≈ 2.26 × 10⁸ m/s. Ordinary glass is about 1.5, and diamond is about 2.42, which helps make it so sparkly.

When light slows, its frequency stays the same but its wavelength gets shorter. If it enters at an angle, one side of the beam slows before the other, so the beam bends. This bending is refraction, and it is why a straw in a glass of water looks broken.

Light trying to leave a dense material at a shallow angle can be reflected completely back inside. This total internal reflection traps light in optical fibres, carrying internet data across oceans.

Equations

\[n = \frac{c}{v}\]
SymbolMeaningUnit
\(n\) refractive index —
\(c\) speed of light in vacuum \(\mathrm{m/s}\)
\(v\) speed of light in the material \(\mathrm{m/s}\)

Sources

  1. OpenStax University Physics Vol. 3 — The Propagation of Light
  2. NIST CODATA — speed of light in vacuum c
  3. Wikipedia — Refractive index

Field notes

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