When waves of any type are obstructed, diffraction occurs.
Diffraction of waves occurs when waves of any type are blocked, obstructed or when the waves need to bend in order to continue. The basic three types of waves are mechanical waves, which travel through air, water or some other physical structure; electromagnetic waves, which don't require a medium to travel, such as light or radio waves; and matter waves, which are produced by electrons and particles. Diffraction can occur with all of these types of waves.
Optical Diffraction
You can create simple diffraction experiments involving light by shining a light through a slit that you create with two obstructive objects. The University of Rochester Institute of Optics says that in optic diffraction, when light diffracts off the edge of an object, it creates a pattern of light called a diffraction pattern. You can experiment with light diffraction using a strong flashlight shining through slits or holes in metal, projecting the light on a white screen and recording your results.
Diffraction Experiments Using Lasers
Using the same technique, you can produce a more accurate experiment employing a helium-neon laser or visible laser diode. In addition to the laser, you need a transmission object that partially obstructs the light, and a screen. The screen can be a sheet of white paper, or a white film screen. If you don't have access to a laser of any type, you might try using a laser pointer and keeping your distances short. By shining the laser through various types of openings, you should be able to discern from the resultant light projection what type of opening the light shone through, such as a pinhole, a vertical slit, a narrow vertical slit or a fine wire mesh. Experiment with different types of diffraction openings and record your results.
Ocean Waves Diffraction
Ocean waves also experience diffraction when they encounter an obstacle such as a breakwater or the side of an island, causing the water to change course. To experiment with ocean wave diffraction, use two floating objects such as a rubber ball or old basketball. Throw the ball into the ocean from the end of a breakwater, toward the side of and preferably beyond the horizontal longitudinal plane of the breakwater. From the beach directly in front of where you threw the ball, record the path the ball takes. If possible, repeat this experiment three times. This will be the control group for your experiment. Next, throw the ball directly in front of the breakwater. Record the path of the ball as the ocean waves bring it to shore. Comparing the horizontal distances of both groups provides a physical summary of wave diffraction as a result of the breakwater obstruction.
Experiments with Sound Waves
The physics department of Georgia State University describes diffraction, as it relates to sound waves, as "the bending of waves around small obstacles and the spreading out of waves beyond small openings." A simple way to experiment with sound wave diffraction is to play a loud, continuous noise from one room, such as rock music. Record the effect of an obstruction, such as a partially closed door. Have a helper slowly turn the sound from low to loud at a specified rate and test the level of sound in an adjacent room and in different locations in the room. You can get an accurate, rather than subjective, reading by using a digital sound-level or decibel meter.
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