13. Physics | Polarization of Light | Optical Activity of Substances | by Ashish Arora

let us now study about an important concept
of optical activity of substances. here we can write. that some specific. transparent substances. have property. to rotate, the plane of polarization. of a
polarized light. when it is passed. through it. such substances which, rotate the plane of
polarization like when polarized light incident onto it and, the light which comes out will
be having a rotated plane i’ll also discuss with the help of some diagrams. but we can write that such substances. are
called. optically active substances. like say if in a tube a transparent glass
tube we fill. an optically active substance. on which when a polarized light is a allow
to incident. which is having its. vibration plane. which i am drawing here it is vertical direction. so when the vibrations, incident onto the
optically active substance this is the tube in which optically active substance is filled. when the light vibrations enters into it then,
as it propagates. the direction of plane. rotates like this. in this situation. here we can say as mush, distance it travels
the. rotation of plane will be more. so finally when the light is coming out the
vibrations will be rotated by some angle. from the initial direction say it is rotated
by theta but in this situation it may be more then. 1 or. more complete turns so it may be theta
or 2-pie plus theta or 2-n pie plus theta. so this is the way how. the rotation. of plane of vibration takes
place here. with respect to the initial direction here
you can see if it is rotating the plane of, vibration in clockwise form. such substances we call. dextro. rotatory. substance. and if finally the light plane which is coming. out of the substance it is rotated in anti
clockwise manner. if in the situation here it is rotating clockwise
if it comes out in anticlockwise rotation. then such substances we call. leevo rotatory substance. and here. with the unit length of. substance, depending on its per unit concentration
which have angle of rotation it produces that we termed as specific rotation by the substance.

Author Since: Mar 11, 2019

  1. sir,how can we be sure that the ppl has rotated clockwise only?.In other view it can seem to be anticlockwise with a larger angle.

  2. sir so dextro and laevo are a function of length of optically active substance used? i.e., a dextro substance can be told to be laevo when the length of substance used is changed appropriately?

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