By measuring the angle e the specific rotation of an optically active substance can be determined. Just after the convex lens there is a Nicol Prism P which acts as a polariser. H is a half shade device which divides the field of polarised light emerging out of the Nicol P into two halves generally of unequal brightness. T is a glass tube in which optically active solution is filled. The light after passing through T is allowed to fall on the analyzing Nicol A which can be rotated about the axis of the tube. The rotation of analyser can be measured with the help of a scale C.
|Published (Last):||8 September 2006|
|PDF File Size:||8.37 Mb|
|ePub File Size:||14.25 Mb|
|Price:||Free* [*Free Regsitration Required]|
That is, angle through which the plane of the polarized light is rotated on passing through a specific length of solution of known concentration. The experimental arrangement is shown if figure, S is source of monochromatic light placed at the focus of convex lens L. The beam, rendered parallel by lens L, falls on called polarizer P. After passing through polarizer P the light His fundamental striking articles at XAmplified are easy-to-understand and helpful enough for Physics-phobic folks Table Of Content Principle It is used for the measurement of the angle of rotation of optically active substance in solution.
General Description The experimental arrangement is shown if figure, S is source of monochromatic light placed at the focus of convex lens L. After passing through polarizer P the light become plane polarized. The polarized light beam passes through a half-shale device H called Laurent plate and then through a tube T containing optically active solution.
White light is used in place of monochromatic light. The left half plate rotates the plane of vibration in anti — clockwise direction, while right-half plate in the anticlockwise direction. Apr 15,
Laurent’s Half-Shade Polarimeter
In essence, the polarimeter consists of a collimated linearly polarized light source S, L and P that is passed through the sample tube T which will rotate the polarization if the sample is optically active , and then polarized A and seen through a telescope E. In this basic setup without the half-shade A you are looking for the maximum and minimum brightness, which then tells you that the analyzer A is precisely aligned with the output rotation. The half-shade H goes between the polarized light source and the sample, and it consists of two half-disks of equally absorptive material. One half, ACB, is glass, and it lets the polarized light pass through unchanged. The usefulness of the half-shade is on the sensitivity of the apparatus. This is the core of the method, and it is replayed over and over again in metrology - you get better measurements with differential measurements of quantities that have a sensitive change with respect to the thing you care about, rather than looking at the extrema where the change is more shallow.
Moogum Often, the sugar refineries use a modified polarimeter with a lauurent cell and used in conjunction with a refractometer called a saccharimeter. In this basic setup without the half-shade A you are looking for the maximum and minimum brightness, which then tells you that the analyzer A is precisely aligned with the output rotation. The position of the analyzer is noted on circular scale. Because many optically active chemicals such as tartaric acidare stereoisomersa polarimeter can be used to identify which isomer is present in a sample — if it rotates polarized light to the left, it is a levo-isomer, and to the right, a dextro-isomer. As the temperature of the sample has a significant influence on the optical rotation of the sample, modern polarimeters have already included Peltier Elements to actively control the temperature. The light after passing through T is allowed to fall on the analyzing Nicol A which can be rotated about the axis of the tube.