So do polarimeters. A polarising filter transmits only light in a certain polarisation direction and suppresses the light of other polarisation directions. Light which has passed through a polarising filter is called polarised. When polarised light passes through a second filter placed parallel to the first filter, the plane of oscillation is maintained and light reaches the screen. Very nice the effect is to be seen when you turn a 3D glasses or a polarised sunglass in front of an LCD computer screen.
At a certain rotation angle the transparency disappears. If the glasses are turned further, the review appears again. Just try it …. Optically active substances change the polarisation direction of the light wave. Optically active are chiral substances which have molecular systems whose asymmetry results are in handedness.
These chiral substances have a pair of nonsuperimposable mirror-image shapes. Examples of optically active media are sugar, lactic acid, quartz, calcite and sodium chlorate. If a tube with no optically active substance is placed between two parallel polarisation filters, the oscillation plane is retained. Light will be visible on the screen at the end. If the tube is filled with an optically active substance, e. This happens because the oscillation plane of the light has been changed.
The reason: sugar solution, as an optically active substance, has rotated the polarisation direction. The angle of rotation depends on the length of the path in the solution and on the concentration of the solution itself and it also depends on the type of sugar. The specific optical rotation for the pure enantiomer is. The instrument used below allows you to calculate the specific rotation, if you know the concentration of the solution.
The cell used for the measurement has a pathlength of It has to be cleaned thoroughly after the measurement was performed and is returned to the teaching assistant or instructor. The instrument has to warm up for at least minutes, if it is not already turned on.
The switch is located in the back of the instrument. The proper wavelength is chosen. The polarimetry cell is filled with the solvent. After filling the cell, the path through the cell should be clear If the path is not clear, the air bubbles in the path have to be removed prior to the measurement. The cell is placed on the rails inside the instrument, all the way on either the right or the left side.
The " Zero button " is pressed to zero the instrument. The screen should show 0. If this is not the case, make sure that the light can pass through. If this does not solve the problem, inform the teaching assistant or instructor about this problem immediately. Then, the solvent is removed and the cell is dried. However, if the light rotates counterclockwise, we call that rotation levorotatory. Look for an internal plane, or internal mirror, that lies in between the compound.
The stereochemistry e. R or S is very crucial in determining whether it is a meso compound or not. As mentioned above, a meso compound is optically inactive, so their stereochemistry should cancel out.
Begin typing your search term above and press enter to search. Press ESC to cancel. Skip to content Home Physics Why sodium lamp is used in polarimeter? Viewed 1k times. Improve this question. Therefore, polychromatic light may give blurry results. Add a comment. Active Oldest Votes. Improve this answer. Farooq M. Farooq Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password.
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