1. For optically active substances
This is equation of straight line inclined at /2 with x-axis. That is with the vibrations of incident light.

2. For optically active substances

3. Practice Problem

4. Specific rotation for liquids
The specific rotation of an optically active substance at a given temperature for a given wavelength of light is defined as the rotation (in degrees) produced by the path of one decimeter length in a substance of unit density (concentration)
The unit of specific rotation is deg.(decimeter)-1(gm/cc)-1
The molecular rotation is given by the product of the specific rotation and molecular weight of the substance.

5. Specific rotation for solids
The specific rotation of an optically active solid substance at a given temperature for a given wavelength of light is defined as the rotation (in degrees) produced by the path of 1 mm length in a substance.
Specific rotation for liquids
The specific rotation of an optically active liquid at a given temperature for a given wavelength of light is defined as the rotation (in degrees) produced by the path of 1 deci-meter length in a substance with density 1gm/cc.

6. A quartz plate cut perpendicular to the optic axis is to be used to rotate the plane of polarized light through an angle of 900. The refractive indices of quartz for right and left handed circularly polarized light of wavelength 7620 Å are and respectively. Find its thickness.
2. If 20 cm length of a certain solution causes right handed rotation of 420 and 30 cm length of another solution causes left handed rotation of What optical rotation will be caused by 30 cm length of a mixture of the above solutions in the volume ratio 1 : 2. The solutions are not chemically active.

7. Polarimeters
A device designed for accurate measurement of angle of rotation of plane of vibration of a plane polarized light by an optically active medium is said to be a polarimeter.
Two Types:
Laurent's Half shade polarimeter
Bi-quartz polarimeter

8. Laurent's Half shade polarimeterV2 T
Two nicols- N1 AND N2
Half shade device-H
Telescope-T
Glass tube-T1 V1
Nicol N2 can be rotated and its position can be noted on a circular
scale with verniers V1 and V2
Monochromatic light after passing through N1 become plane polarized with its vibrations in principal plane of nicol.

9. Laurent's Half shade polarimeter

10. Laurent's Half shade polarimeter

11. Laurent's Half shade polarimeter

12. Laurent's Half shade polarimeter

13. Laurent's Half shade polarimeter

14. Laurent's Half shade polarimeter

15. Laurent's Half shade polarimeter

16. Laurent's Half shade polarimeter

17. Half shade device (H) Y  O X C SPECIFIC ROTATION
Where l is length of tube T1 in cms.

18. Bi-quartz Device
White light source is used.
Two semicircular quartz plates (Right and Left handed) with Optic axis perpendicular to crystal surface (rotation effect only).
Device is designed for yellow color.
YY’ is tint of passes
If Analyzer axes is perpendicular to YY’ then yellow color will be disappeared and we can get resultant of Red and Blue colour (Reddish violet color) as min intensity.
This is much more sensitive and accurate then Half shade device polarimeter. But having major drawback for color blindness person.

20. Bi-quartz Device
Right handed Quartz
Left handed Quartz

21. Bi-quartz Device

22. Bi-quartz Device
White light source is used.
Two semicircular quartz plates (Right and Left handed) with Optic axis perpendicular to crystal surface (rotation effect only).
Device is designed for yellow color.
YY’ is tint of passes
If Analyzer axes is perpendicular to YY’ then yellow color will be disappeared and we can get resultant of Red and Blue colour (Reddish violet color) as min intensity.
This is much more sensitive and accurate then Half shade device polarimeter. But having major drawback for color blindness person.