refracLatin “frango,” = I break, as in fracture. The straws look broken as we view them through the water. The light from them is being refracted, changing direction and travelling more slowly in the water than the air around it.

How it works

soldierImagine two columns of soldiers marching in step side by side on the pavement. The pavement then changes into a muddy path. The soldiers nearer the path have to take smaller steps to stay in time so travel more slowly, resulting in the whole column changing direction. Light travelling from a less dense to a more dense medium slows down. If the angle between the media isn’t 90 degrees, the beam suffers a change in direction as well.  Light waves are refracted towards the normal when going from less dense to more dense material (air into glass or water) and vice-versa. Water is refracted towards the normal when travelling more slowly in shallower water. If we look at a ripple tank pattern the waves travel more slowly in the shallower water. If they enter the shallow water at an angle the wavefront’s direction changes.

refraction_imagelargeWe can see the shorter wavelength and change in direction at the top of this image very clearly where the speed is slower. There’s no change in frequency.


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