# Bending Light

Initial Publication Date: August 15, 2008

#### Summary

In this physics lab students will observe light bending as it enters a medium. Students will then be able to calculate the angle of the bent light and compare that with other students observations for like and different mediums.

## Learning Goals

This activity is designed to reinforce the idea that light can bend. This activity is also designed to allow students test the refraction of light in different mediums and make predictions about those amounts of refraction based on characteristics of those mediums (density, viscosity, depth, etc.).
The students will need to use analytical reasoning skills, observational skills, and data collection skills.
Key concepts to be reviewed for this activity are:
The Law of Reflection: the light waves will always reflect so the angle in is equal to the angle out.
Refraction is a change in the direction of light waves as they pass from one medium to another. This change in direction or bending is caused by a change in the speed of light as it travels through different mediums.
The vocabulary words associated with this activity are refraction, reflection, and viscosity.

## Context for Use

This activity is best suited for a high school physics classroom. The class size doesn't matter too much, because all of the materials are simple and inexpensive. The students should work in groups of two to three.
This can be done as a structured lab or as an exploratory lab, depending on the ability of your students. This lab can be completed in one 50 minute period. It can be extended to another period if more exploration is needed.
The students should be familiar with or have access to the densities and viscosities of different liquids. The students should also be able to calculate angles.
This activity is taught during the optics portion of a physics curriculum. This could be used in earth or environmental science also as a demonstration of how sunlight (and its path) can be affected by an alteration of the medium in which it travels, possibly due to pollution.

## Description and Teaching Materials

In this activity students will be able to observe that light bends. Students can also calculate the index of refraction for different materials, or try to hypothesize the index of refraction of different mediums based on physical properties of those mediums.
Materials:
Each lab group will need:
1 or 2 Styrofoam or paper cups
One 1 ¾ inch galvanized washer
A pole or meter stick secured to the end of a lab table
Procedure:
The students will secure a pole or meter stick at the end of a lab table or desk. The students will decide who the observer will be and at what height the observer will rest their eye at.
Place the washer flat in the bottom of the cup.
Cover about half of the top of the cup with masking tape.
The observer places their eye at the predetermined height on the meter stick/pole.
Place the cup at the base of the meter stick/ pole so that the open half of the cup is furthest from the observer.
The non-observing student begins to slide the cup away from the observer's eye.
The observer must notify their partner as soon as he/she sees just the edge of the washer while looking over the edge of the tape.
The students should measure the distance from the observer's eye to the top of the cup and then the distance from the meter stick/ pole to the furthest edge of the tape. This will give two sides of a right triangle. The students can then calculate the third side and the angles of the triangle.
Using the Law of Reflection, the students should know that the angle at which the light went into the cup is the angle at which it came out.
Next the students should fill the cup with water so that it is just below the masking tape. If the masking tape gets wet, a meniscus will form and alter the calculations.

The students should slowly slide the cup from the observer's position. The light is now refracted because of the water, so the cup can be pushed further away and the washer will still be visible. When the light leaves the water the ray will be bent away from the "norm". Students can calculate a new angle at which the water leaves the cup, using the same methods as before. This new angle and the original angle can be used to determine the index of refraction.
After calculating the index of refraction, I allow students to repeat this process with a variety of mediums. I use rubbing alcohol, corn syrup, oil, etc. It really is up to you how much they explore. The students can also begin to try and make relations between mediums, their viscosity, density, and index of refraction. This can be applied to earth and environmental science to show the impact different substances in our atmosphere may have on the light that passes through our atmosphere from the sun.
Before testing other mediums, students should hypothesize bout the index of refraction for mediums based on that particular medium's characteristics.
The best description that I found for this activity is at:
http://www.millersville.edu/~physics/exp.of.the.month/12/

## Assessment

I will collect the students' written lab observations. I will likely ask the students to compare and contrast two of the mediums observed ad attempt an explanation as to the differences in their index of refaction.

## Standards

II. PHYSICAL SCIENCE E. Forces of Nature 1.Factors that affect the presence and magnitude of electromagnetic force.

III. EARTH AND SPACE SCIENCE A. Earth Structure and Processes 3. how processes have played significant roles in determining the character of the atmosphere, biosphere, hydrosphere and lithosphere over time.