How we can prove that a light ray passes through the optical centre of a lens undeviated ?

Answer 1

Using spherical lenses, the sides of the lens are parallel at the midpoint. This means that the ray going through it does so as if it is ordinary plate window glass. Be careful, because you CAN'T prove that this light is undeviated. If you do the math (snell's law twice) you'll find that the ray proceeds in the original direction, but is slightly offset. The offset depends explicitly on the thickness of the lens. Let me guess you're working with THIN lenses? Thus, this offset is "negligible" and the ray can be approximated as undeviated through the center.

Answer 2

The key in the question is the "not parallel" part. A light ray that travels along the centerline of a lens, convex or not, doesn't bend because it meets both surfaces of the lens at a right angle. Unless the lens has an index of refraction equal to the medium surrounding it, that is the ONLY ray for which this is true. Figure your light paths according to the surface angle, just like any other place on the lens.

Answer 3

Our teacher told us dat the refractive index at the centre is highly negligible as compared 2 dat of d rest of the mirror.......
So the ray of light that passes thru it is considered as UNdeviated

Answer 4

Read "Nodal points" in this site.


http://en.wikipedia.org/wiki/Optical_centre

Answer 5

You can use the Fermat Principle .