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Of incidence is equal to the angle of reflection

Refraction. - Experiments have shown that light travels with the greatest speed in a vacuum and that it travels with different speeds in different mediums. When it passes obliquely from one medium to another in which it has a different velocity, there occurs a change in the direction of propagation of the light. This bending of the ray of light when passing from one medium to another is known as refraction.

Refraction can be illustrated by taking a cup which is opaque (Figure 38) and placing a coin on the bottom of it at the point B, so that the far edge of the coin can just be seen when the eye is at E. If now, without moving the eye, water is poured into the cup, the coin will come completely into view. The ray BA as it leaves the water is bent away from the normal NA. Other rays are bent in a similar manner, and an image оf the coin is formed at C, so that the depth of the coin below the surface of the water seems to have been lessened. Here it is seen that rays coming from the water to the air are bent away from the normal. The rays are always bent away from the normal when they enter a medium in which their velocity is greater than it was in the medium from which they came.

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