Submitted by: Amber van den Raadt

Position: N/A

Institution: Azusa Pacific University

Title of Experiment: Light Diffraction

Materials Needed:

2 new wooden pencils

piece of transparent tape

candle

Scientific Background of Experiment:

Diffraction is the way light behaves when it is limited by lateral objects. It is the movement of light around objects. Luckily a unique characteristic of light is that it bends. Diffraction is this name given to this bending of light. In this experiment the students will learn about diffraction with the pencils and flashlight. To show the wavelength properties of light, students will notice the diffraction pattern. The diffraction pattern is the pattern of light and dark created when light bends.  

Methodology:

The student will start by lighting the candle using caution with the open flame. Place the light about a foot and a half away from the student. Take the piece of tape and put it around one of the pencils just below the eraser. This will create a slit when the pencils are placed next to each other. Hold the two pencils side by side in front of the student, with the erasers at the top. Now bring the two pencils about an inch away from the eye and look at the candle through the slit. Squeeze the pencils together making the slit as small as possible while still looking at the candle. Notice anything? Now keep looking at the candle, and rotate the pencils from vertical to horizontal. Notice anything else? You should have seen a horizontal line of light when the pencils were vertical, and a vertical line of light when the pencils were horizontal. Look closely at the line. Do you see anything? You should be able to see tiny bits of light. As you squeeze the pencils together you see the bits of light grow larger and spread apart. The farther away from the candle you look the easier the bits of light are to see. Notice the colors that appear in the light? What colors are they, and what is unique about the pattern that they appear in?

Misc. Helpful Information/ Hints/ Suggestions:

The waves associated with light are seen because of the black bands between the bits of light. The diffraction pattern that you see are produced by the light waves that go through the slit and spread out. The light overlaps and interacts in complex ways. The students should have noticed the blue light on the inside of the bits of light, and red light on the outside of the bits of light. This is because the wavelength of red light is longer than that of blue light. Since the wavelength of the light is proportional to the angle at which the light bends, it makes sense that the red light is on the outside, and the blue light is on the inside.