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Refraction Analogy

This analogy is not perfect, but it may give you some insight into why light refraction occurs.

Imagine a large athletic area with 2 parallel football fields. The surface of the two fields of play is artificial grass, but the area between the 2 playing fields is tall grass and weeds.

Four girls, arms linked at the elbows, are walking quickly across the field of play on the left. When the group approaches the edge of the first field, the girl on the extreme right gets into the tall grass first. She has to slow down. The girls on her left continue at the higher speed. Because those 3 girls are going faster, they change course slightly, pivoting around the slower girl, rather than disconnect. Eventually they all are in the unmowed grass and are walking slowly on a new course that is closer to perpendicular to the interface between the 2 surfaces. When the group reaches the second field of play, the girl on the right again reaches the boundary first and immediately resumes the higher speed. Because the other 3 are still walking carefully in the tall grass, the girl on the right has to change course rather than disconnect. When all 4 are on the artificial grass, they are on a course that is parallel with their original course but diverted off to the side.

A wave front changes direction as it enters a slower medium.

This is an analogy. The hope is that it helps you remember that refraction occurs when it enters a medium in which the speed of light is different from the medium (or the vacuum) that it had been going through. And that it helps you remember which way light bends when it enters a different medium.

copyright: Steve Johnson, sojphysics@gmail.com

Steve Johnson is an electrical engineer. He earned a B. Sc. in Physics, and MS Electrical Engineering. Steve welcomes your questions.

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