Color and Light

11 March 2013

Yesterday I discussed polarization of light and how it can be used to determine the position of the Sun, even on a cloudy day. This works because sunlight is polarized when it scatters in the air.

There are lots of materials that can affect the orientation of light. One of the more interesting effects can be seen with corn syrup or other kind of sugar water. Because sugar molecules have a handedness to them, polarized light changes orientation as it moves through the corn syrup. The polarization twists as it moves through the corn syrup. However the rate at which the light twists depends on the color of the light. This means the polarization is spread apart by color, similar to how a prism spreads out the colors of light by direction. You can’t see this effect normally, but if you look at the light through a polarizing filter you can see the colors vary by orientation, as shown in the video below.

If you did a careful measurement of the spread of color, you could measure how much corn syrup the light has passed through. The more corn syrup it passes through, the greater the spread of colors.

We can use the same effect effect in radio astronomy, but I’ll talk about that next time.