Quantifying Refraction
By controlling the material we pass light through, we can predict the angle at which it will bend.Copyright 2011 Epzcaw, Wikimedia Commons http://commons.wikimedia.org/wiki/File:Diffraction_of_laser_beam_by_grating.jpeg
Students learn the relevant equations for refraction (index of refraction, Snell's law) and how to use them to predict the behavior of light waves in specified scenarios. After a brief review of the concept of refraction (as learned in the previous lesson), the equations along with their units and variable definitions, are introduced. Student groups work through a few example conceptual and mathematical problems and receive feedback on their work. Then students conduct the associated activity during which they practice using the equations in a problem set, examine data from a porous film like those used in biosensors, and apply the equations they learned to a hypothetical scenario involving biosensors.
In engineering, it is not enough to merely understand the concepts or ideas behind physical phenomenon such as refraction. If engineers want to take a physical law of the universe and turn it into a product that performs a task, then the phenomenon must be quantifiable—they must be able to assign a mathematical function or equation to it that accurately predicts an outcome if the input parameters are manipulated purposefully. In a way, engineers are dictating the setup and letting nature take its course to a conclusion that the engineers can foresee from the start. Similarly, students play the role of engineers in this lesson when they use an equation for refraction (Snell's law) to predict what light will do given a specific scenario. They further act as engineers when they use this equation to define what a biosensor can be made to do under given conditions.
After this lesson, students should be able to:
- Solve Snell's law problems for a single variable.
- Accurately draw the path a light ray will take when given the index of refraction of the substance(s) through which it travels.
- Accurately describe how the path of a light ray changes when the index of refraction of the substance(s) and/or the incident angle are changed.