Optical activity
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Some substances rotate the plane of polarisation.
Certain substances (sugar solutions, quartz) rotate the plane of polarisation. The rotation is proportional to path length and concentration, measured in polarimeters.
Used in the sugar industry.
Different enantiomers rotate in opposite directions.
In more detail
Optically active substances rotate the plane of polarisation of light passing through them. Sugar solutions and some crystals show this effect.
Real-world uses
- Polarimeters measure sugar concentration using optical activity.
- Pharmaceutical quality control uses optical activity to check chirality.
- Sugar solutions rotate polarised light, which chemists use to measure the concentration of a sample.
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Frequently asked questions
Why do some substances rotate light?
Their molecules are chiral, so they interact differently with left and right circular polarisations.
What is a polarimeter?
An instrument that measures the rotation of polarised light by a sample.
How is the rotation used in practice?
A polarimeter measures the angle of rotation, which depends on the concentration of the optically active substance.
Related topics in Optics
Brewster's angle · Polarisers and LCDs · Birefringence · Coherence and lasers · Holography · Fermat's principle