why ray through center of lens passes straight through

Physics
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Why does the ray through the center of lens passes straight through and doesn't refract? Wouldn't it have to refract because it's coming from a medium of lower refractive index to one of higher refractive index?

Jan 5th, 2015

Upon reaching the front face of the lens, each ray of light will refract towards the normal to the surface. At this boundary, the light ray is passing from air into a more dense medium (usually plastic or glass). Since the light ray is passing from a medium in which it travels fast (less optically dense) into a medium in which it travels relatively slow (more optically dense), it will bend towards the normal line. This is the FST principle of refraction. This is shown for two incident rays on the diagram below.

Once the light ray refracts across the boundary and enters the lens, it travels in a straight line until it reaches the back face of the lens. At this boundary, each ray of light will refract away from the normal to the surface. Since the light ray is passing from a medium in which it travels slow (more optically dense) to a medium in which it travels fast (less optically dense), it will bend away from the normal line; this is the SFA principle of refraction


Jan 5th, 2015

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Jan 5th, 2015
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Jan 5th, 2015
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