Barber Pole Effect

A beam of polarized light is passed through a cylinder of corn syrup containing a few grains of silver nitrate. The sugar solution rotates the plane of polarization depending on wavelength and depth, creating a colorful helical pattern that rotates with the polarizer. Viewing through an additional polarizer enhances the effect.

1. See methods give in the Links section below.

This tests your understanding of light | The barber pole effect - 3Blue1Brown:

The Barber Pole: a sugar-induced rainbow - QuinnPhys:

📄 BARBER POLE DISPLAY - oberlin.edu: https://www2.oberlin.edu/physics/catalog/demonstrations/optics/barberpole.html

• Replace white light with a monochromatic source (e.g., laser) to study periodic intensity changes.
• Use different concentrations of sugar solution to see how the degree of rotation changes.
• Try alternative optically active solutions such as fructose or tartaric acid.

• Use caution with electrical equipment (motor, power supply, projector).
• Avoid looking directly into bright light sources or lasers.
• Ensure glassware (cylinder) is securely mounted to prevent spills or breakage.

• Why does the sugar solution rotate the plane of polarization? (Because sugars are optically active molecules that interact asymmetrically with polarized light.)
• How does the depth of the solution affect the observed rotation? (Greater path length produces more rotation.)
• Why does adding silver nitrate improve the display? (It scatters the light, making the helix visible, and also inhibits bacterial growth.)
• What happens when you view the setup through a second polarizer? (Colors become more saturated as scattered light is filtered.)
• Why do maxima and minima appear when a laser is used? (The interference pattern arises from constructive and destructive polarization effects.)