Light rays propagate rectilinearly, as can be seen with micro-particles of powder, talcum powder, or smoke in a medium with a laser beam.Why is the laser light in the Plexiglas pan filled with water be curved?
Refraction of light.
12 to 18 years old.
Expected time for the mystery
Approximate time for teacher preparation: two hours.Approximate time in classroom: three or four individual 50-min lessons.
Laser pointers have to be handled with care and never directed at people’s eyes.Disclaimer: the authors of this teaching material will not be held responsible for any injury or damage to persons or properties that might occur in its use.
Preparation and list of materials
Laser pointers, talcum powder, plexiglass pans, glass prisms, plexiglass prisms, glycerol, water, sugar syrup, milk, mineral oil, alcohol, water tanks.To prepare the mystery, put 3 to 4cm of glycerol (better) or sugar syrup at the bottom of the Plexiglas pan and then add water without stirring. After about one hour of rest (it can work better after some hours or even after days), a density gradient of glycerol will be present in the pan. Throw the light of a green laser beam longitudinally through the pan near the interface between the glycerol and the water; adjusting the direction of the beam, you will see it curved towards the bottom. To better visualise the trajectory of the light, add a touch of skimmed milk to the two liquids.
- Qualitative behaviour of light when the medium in which it propagates changes its refraction index.- Quantitative evaluation of the behaviour of light in refraction by means of Snell’s law.
A very clear tutorial about the refraction of light can be found on YouTube: