Hands On Physics
In this activity, you simulate a hazy atmosphere with milky water. By shining
light through the water and carefully observing what happens, you gain important
insights about haze in air.
The "Milky Way": Scattering in Water.
In this activty, you investigate light scattering. You simulate a hazy atmosphere
with milky water. By shining light through the water and carefully observing
what happens, you gain important insights about haze in air. Milk cosists
of tiny droplets of fat that are about the same size as haze particles,
so putting milk into water is a good way to model a hazy sky. Start with
clear water and then add drops of milk, a few at a time. Predict and then
observe changes in the intensity and color of the light, as the amount of
milk increases. Keep track of both the light that goes straight through
and the light that gets scattered out the side.This is a model for the scattering
caused by haze in air. Later on you will investigate whether milky water
resembles hazy air.
Questions to think about:
- How does milky water influence the color and intensity of light passing
through the water?
- How does milky water influence the color and intensity of light scattered
by the milk particles?
- How does a clear tint influence the color and intensity of transmitted
and scattered ligh
You need a clear container for water, milk, water tints, a bright light,
and some polarizers. The idea is to shine light through at least 20 cm of
water onto a white surface. You will want to be able to add milk in equal
amounts. An eye dropper to measure out the milk would be helpful.
The container can be a graduated cylinder, a glass milk bottle, an aquarium,
or a clear tube sealed at one end with plastic. Whatever you use, it is
important to be able to shine the light down through at least 20 cm of water,
to look in the side to see the light beam, and to see the amount of light
that gets through and falls on a white card.
Scattering in Water
The light source can be a flashlight, a reading lamp, or a slide projector
with a mirror to direct the light down through the water.
Projector as Light Source
We need some way to color water. You can use food coloring, water colors
used in painting, or colored chemicals like copper sulfate.
These activities are designed to help you see how light is effected when
it travels through clear liquid and and then when it travels through murky
liquid. Observe the intensity and color of the light that goes straight
through the liguid as well as the light that is scattered out to the side
Questions to think about:
Start by shining light through clear water. Experiment with a clear water
colored with a tint such as a food color. Now add a small amount of milk
to clear water and observe what happens. Continue adding the same amounts
- Which scatters light most, clear or murky liquid?
- Are all colors of light scattered equally?
- Is most light polarized?
- Where do you observe polarized light in nature?
- Does polarized light stay polarized when it strikes different surfaces?
- What do you think "partially polarized" means?
- Is the light that goes through milk become polarized?
- Is light scattered off milk polarized?
Investigate the polarization of scattered light. If you are not familiar
with polarized light, start by exploring with the polarized filters. When
you look at a source of light through a polarized filter, you see only light
polarized in one direction. Look around you, through a polarized filter,
and rotate the filter to check for polarization.
If you see no changes as you rotate the filter, then the light you are
observing is randomly polarized. Look at the sky, at haze, at light reflected
off water (glare). Make polarized light by placing a polarizer in front
of a light source. Look at the polarized source through your filter as you
rotate it. Look at various surfaces illuminated by polarized light. Finally,
shine unpolarized and polarized light through the milky water.
Keep a journal as scientists do, even when messing around. Record all your
questions and observations in a bound notebook. Don't erase, just cross
out errors. Write enough so someone else could reproduce your experiments.
Diagrams can save lots of words and help make your ideas clear. If you make
measurements, record your data, with units. Tables are useful for repeated
similar measurements. To make the logic of any calcuations clear, first
record the formula you used, then show the numbers used to evaluate the
formula, and finally your answer.
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