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# To measure the index of refraction of some small transparent chips of plastic of irregular shape, a physicist places the chips in a glass beaker full of water. She then gradually adds sucrose to the water until the chips suddenly become nearly invisible. Explain why a measurement of the index of refraction of the sucrose solution then yields the index of refraction of the chips of plastic.

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We can see plastic chips in water due to refraction of light on them. Light rays reaching our eyes are distorted due to the presence of an object and we can form an image of whichever transparent material is submerged in water.

The index of refraction of a solution is initially 1.33 (pure water). Adding a sucrose to the water increases the refraction index of a solution (sucrose + water). This index of refraction at some point becomes equal to the index of refraction of the unknown material. At this point object becomes invisible because no light rays refract on it edges and light rays travel as if there were no obstacle on its way.

Therefore, index of refraction of a solution and that of a plastic chip are equal when object is invisible. Hence, we only need to measure an index of refraction of a solution.

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