Two of the number of processes light undergoes when it interacts with matter is reflection and refraction. Depending on the property of the matter it interacts with, light either bounces back (undergoes reflection) or it passes through the matter but its speed and direction may change–called refraction. The consequence of these simple processes can be from just unusual to dramatic in real life.

The Discrepant Event: Stray Straight Straw

This discrepant event is the most challenging in the series. This one involved inserting a drinking straw into a beaker of water and observing its appearance.

straw in beaker - vertical straw in beaker - at an angle
Fig. 1. Appearance of a drinking straw inserted straight down a beaker of water. Fig. 2. Appearance of the same straw inserted at an angle.

And the question is:  Why does the part of the straw submerged in water appear thicker?

Extension 1. In figure 2, why does the part submerged in the water appear to be broken off from the part above?

Extension 2. For this, you have get a straw (or a pencil) and water-filled glass. Insert the straw straight down the middle of the glass as shown on figure 1. Now. slowly move the straw, still vertical to the left. Observe the appearance of the part submerged. Next, bring it back to the center and now slowly move it to the right. Again, observe the appearance of the part submerged. You will have noticed a difference between the two. What’s the explanation for the difference?

Concepts involved:

  • image, normal, rare medium, dense medium, reflection, refraction, angle of incidence, angle of refraction, speed of light, line of sight (Additional advanced concepts: refractive index)

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