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the object distance is smaller than the image distance because for the image to be formed the rays must move a longer distance. Image distance is greater than object distance.

Snell's law states that the ratio of the sines of the angles of incidence and refraction is equivalent to the ratio of the phase velocities in the two media, or equivalent to the opposite ratio of the indices of refraction:

with each θ as the angle measured from the normal, v as the velocity of light in the respective medium and n as the refractive index of the respective medium

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