MATERIALS:
bag of uv-beads (Prof.Bunsen, $15);
UV-light
or torch; sunlight if possible; ordinary torch
petri
dishes, zip-lock bags or acetate sheets;
sunscreens
with diff. SPF.
SAFETY NOTES: Do not stare into the UV light for long
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Testing beads
1.Show
the students UV-beads and ask for any
observation
2.
Place a small handful of beads on the table and turn on the UV light for few
seconds. Ask about changes. What do they think caused the changes?
Shine
an ordinary light (torch) on the beads (no colour change)...
3.
Tell the students about ultraviolet light
4. Have
the students take the beads outside in the Sun. Ask why they think the beads change colour
in the Sun.
Give
each pair of students a few beads. Have the students put the beads in a
pocket or other dark place. Tell to face away from the Sun and take out the
beads. Make sure they keep the beads in their shadow. Ask why the beads changed colours even though they
were in the shadows?
5. Tell
the students that ultraviolet light is scattered (bouncing off particles) in
Earth’s atmosphere. Some of this UV light ends
up
bouncing into areas that are in shadow. Therefore, the beads will change colours
even if they are in shadow!
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Sunscreen Test
With the
different SPF (Sun Protection Factor) numbers available, we want to lotion
really works best at keeping out the sun's harmful UV rays?
We used
two sun-blocks: Lacura15+ and Everyday
30+ and UV Beads to determine the
blocking potential of the sunscreen.
Place
the beads in a zip-lock bag (or petri-dish) and apply a layer of sunscreen to
the outside of the bag. Use a permanent marker to write the SPF number of the
sunscreen you're testing on the outside of the bag. Be sure to set up one bag
without any sunscreen coating for comparison (the CONTROL). Expose the beads to direct sunlight (or shine UV-light)
for 5 minutes and look for any changes in color.
NOTEs: Some
may claim that the sunscreen blocks UV light because you can’t see through
it. It was found (see the Ref. ) that cream cheese is a substance that blocks
visible light but not UV light.
Pill bottles
block UV light so the drugs inside are not damaged.
Extension: There are many substances that allow
visible light to pass and block UV light. You
can
test items such as windows, car windshields, and sunglasses to see which
allow UV light to pass through and which block UV light.
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Teacher’s Notes:
UV
sensitive beads contain pigments that change colour when exposed to
ultraviolet light.
The colour
of the beads becomes deeper when it is exposed to more intense UV light.
Our
atmosphere scatters light. Short wavelength light is scattered more than long
wavelength light. Scattering of short wavelength blue light is why our sky is
blue. UV light has an even shorter wavelength so it is scattered even more
than blue light. If your eyes could detect UV light, you would see UV light
coming from every direction in the sky!
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Materials
Three teaspoons
of white vinegar
One medical
latex glove (or balloon)
Two teaspoons
of baking soda
A glass jar,
flask or a bottle
*30 ml vinegar + 1tsp baking
soda is just fine (KN)
Procedure
Fill the jar with three tablespoons of white
vinegar.
Take out one glove from the box and pour two
tea spoons of baking soda inside. (use funnel)
Wrap the base of the glove over the mouth of
the jar, making sure that no baking soda falls in just yet.
When you are ready, take the attached glove
and put it inside the jar. What happens?
—The Scientific Explanation
When vinegar and baking soda are mixed in a container, they react violently. The balloon (or GLOVE) blows up because a gas called carbon dioxide is created and given off when you mix the baking soda and vinegar.
Research
Questions
·
What do you think will happen when baking
soda and vinegar come in contact (what will be produced)?
·
What do you think will happen to the
balloon attached?
· Why does the balloon stop blowing up (why
does the reaction stop)?
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