Background. Things to think about
as you mess around
Questions. Challenge questions
which the messing around investigations are designed to answer
Tools & Materials.
Lists, descriptions, and suggestions for the use of tools & materials
need for messing around with light
Investigations. Hands-on
activities to help you learn about properties of light which are important
for the study of haze.
More of the Story: Initial Investigations
Pollution of light sources (most notably the sun) are of some concern as
we look into the future and think that nuclear war or continued use of combustion
engines or industries or even natural disasters like volcanic eruptions
might BLOCK the wonderful sunlight we now enjoy and "take for granted".
Notice how one hardly ever wonders whether the next day is going to have
light instead of dark. One hardly ever wonders whether night will continue
through the next day except perhaps our colleagues closer to the North or
South poles where weeks of sunlight or darkness exists. Some who work and
study in polluted areas are very aware of the pollution because it tends
to partially block the sun.
In Mexico City, Mexico, pollution gets trapped because of the mountains
on three sides of the city. When it rains, the pollution comes back down
onto the city. Unfortunately rain can be absent for a long period of time
in Mexico City.
In Warsaw, Poland, pollution is bad and it is hard to breathe sometimes.
In Los Angeles, California, U.S.A., some people wear gas masks to
protect themselves from the bad air.
In Concrete, Washington, U.S.A., the houses were covered with a layer
of concrete which at one time was dust in the air and blocked the sun completely.
It is the bad air that rises and gets to the upper reaches of the troposphere
(that layer of air where we live and breathe). Sunlight is partially blocked
but such pollution. We call the phenomena - haze.
Background
We are attempting to eventually find out the amount of haze in our local
area and to record this data at regular intervals to provide a much needed
database for students and scientists around the world.
To study haze, you need to know about light. We are concerned here with
some of the properties of light as we consider haze and light pollution.
Linear propagation
Intensity
Reflection
Refraction
Scattering
Diffraction,and interference
Wavelength, speed, and frequency
Energy
Questions
You will be determining the amount of haze in the air by measuring light
intensity. What problems arise when measuring light intensity, and how can
you eliminate these problems? These are some of the questions about light
that you will need to answer before you start to study haze.
What units are used for light intensity?
How is light "intensity" related to distance from a light
source?
How does ambient light affect the measurements?
What is the relationship of particle density vs. light intensity?
How might you measure the intensity of specific wavelengths of light
from the sun?
Investigations:
The first thing you do in a HOP unit is "messing around". This
part of the unit gives you a chance to gain an understanding of the basic
ideas without having to worry about running detailed experiments. This can
be fun, but still quite serious. Keep your eyes open, ask lots of questions,
and write down your observations. You should always be asking yourself
"Why are we doing this?",
"How does this realate to haze?", and
"What do I expect?"
There are four investigations in this section. You explore how light is
spread out (scattered) when it shines past small particles, and you investigate
several light souces and several detectors of light. You build some electronics
for detecting light, and you study color .
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 haze unit uses a number of different light sources and detectors.
In this activity, you investigate a photoresistor and get a feel for how
light detectors operate.
The detector used in the haze experiment is not very sensitive to
light, so you will need to amplify its output. This activity shows how to
do this with a simple electronic circuit that uses an important kind of
chip, called an operational amplifier, or opamp.
Light consists of different colors that can be separated out into
a spectrum. In this activity, you will create a spectrum and find out how
different materials and detectors respond to the different colors.
Hands On Physics