Bécher Invisible (Correspondance d'Indice de Réfraction)

Rendre un objet en verre invisible en l'immergeant dans un liquide d'indice de réfraction identique

Classroom Demonstrations Beginner (Middle School) 15 min ~$8,00

Objectif

Démontrer le concept d'indice de réfraction en rendant un objet en verre invisible dans un liquide dont l'indice de réfraction correspond au sien.

Contexte

We see transparent objects like glass because light bends (refracts) at the surface where the glass meets air. The degree of bending depends on the difference in refractive index between the two media. If a glass object is placed in a liquid with the same refractive index, light passes through without bending, and the object becomes effectively invisible. Pyrex glass (n ≈ 1.474) nearly matches vegetable oil (n ≈ 1.47), creating a stunning visual effect.

Avertissements de sécurité

  • Vegetable oil is slippery — clean up spills immediately to prevent falls
  • Glass objects can break — handle with care

EPI requis

goggles

Matériaux

  • Vegetable oil (or glycerol) (500 mL)
    Refractive index ≈ 1.47
  • Pyrex glass beaker or rod (1)
    To disappear
  • Regular glass rod (1)
    For comparison (different n)

Équipement

Large glass beaker (1 L) or clear container

Procédure

1

Fill the large beaker about 2/3 full with vegetable oil.

2 min
2

Show the Pyrex glass object to the audience. Note that it is clearly visible in air.

1 min
3

Slowly lower the Pyrex glass into the vegetable oil. As it submerges, it gradually becomes invisible.

3 min Lower gently to avoid splashing
4

For comparison, lower the regular glass rod into the same oil. It remains visible because its refractive index does not match.

3 min
5

Discuss: light refracts at boundaries between materials with different refractive indices. When n values match, no refraction occurs and the object seems to disappear.

6 min

Résultats attendus

The Pyrex glass becomes nearly invisible when submerged in vegetable oil. Only slight distortions at the edges may be visible. The regular glass rod remains clearly visible in the same oil.

Nettoyage

Remove glass objects and wash with dish soap. Oil can be saved for reuse or disposed of in general waste. Wipe up any oil spills.

Détails

Catégorie
Classroom Demonstrations
Difficulté
Beginner (Middle School)
Durée
15 min
Coût estimé
$8,00
Étapes
5
Matériaux
3

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Frequently Asked Questions

What is the objective of Bécher Invisible (Correspondance d'Indice de Réfraction)?
Démontrer le concept d'indice de réfraction en rendant un objet en verre invisible dans un liquide dont l'indice de réfraction correspond au sien.
How difficult is Bécher Invisible (Correspondance d'Indice de Réfraction)?
This experiment is rated as Beginner (Middle School). It takes approximately 15 minutes to complete.
What safety precautions are needed for Bécher Invisible (Correspondance d'Indice de Réfraction)?
Key safety precautions include: Vegetable oil is slippery — clean up spills immediately to prevent falls; Glass objects can break — handle with care.
What materials are needed for Bécher Invisible (Correspondance d'Indice de Réfraction)?
The main materials required are: Vegetable oil (or glycerol), Pyrex glass beaker or rod, Regular glass rod.
What results should I expect from Bécher Invisible (Correspondance d'Indice de Réfraction)?
The Pyrex glass becomes nearly invisible when submerged in vegetable oil. Only slight distortions at the edges may be visible. The regular glass rod remains clearly visible in the same oil.