Science Buddies: "Ask an Expert"

I am doing the leaves and light project with my son. (I have copied the instructions for you to view.) My question is about step number 8.
We have learned, with background research about light, that the colour you see is the colour reflected.
Step 8 seems to says the opposite. I am confused. I do not know how to explain this to my 8 year old son. Who asked the question in the first place.

Thanks for your time.

Steph

Experimental Procedure
1. In this experiment you will be covering the leaves of your houseplant with sleeves of differently colored clear plastic, or with black construction paper as a control group. First you will need to make the different colored sleeves for your experiment.
2. Using your permanent marker, color one sheet of transparency film completely with each color. When you are done, you should have one red sheet, one yellow sheet, one green sheet, and one blue sheet. You will also need to keep one clear sheet as a control group.
3. Cut the different colored sheets (clear, green, yellow, blue, red, and black) into six squares by cutting each sheet in half along the length and into thirds along the width.
4. Place two squares of the same color together and tape with the scotch tape along three sides, making a sleeve. When you are finished you should have three sleeves of each color.
5. On your houseplant, place the sleeves over the leaves one at a time. Try to space the different colored sleeves out upon the plant. Each time, secure the sleeve to the stem by taping the open side shut with scotch tape.
6. Place the houseplant in a sunny window for one week, rotating the plant every day.
7. After one week, carefully remove the sleeves from the plant one at a time, each time noting the color of the sleeve and the appearance of the leaf in a data table:

8. Now look at your data and analyze your results. Remember that the color of the sleeve is the same as the light that is being ABSORBED by the leaf, not the color that is being BLOCKED from the leaf. The exception is the black sleeve, which is blocking all of the colors of light from being absorbed by the leaf.

Hi Steph. That's a great question, and I am sure it is confusing for many people. I had to search around for the info so I could give you the answer. The details are here (scroll down to the section about filters and color subtraction): http://www.physicsclassroom.com/class/l ... ubtraction

The background is explaining how it works for opaque materials - like your shirt, the paint on your walls, etc. Filters are transparent, so they work a bit different:
Opaque materials selectively absorb one or more frequencies of light and reflect what is not absorbed.
Transparent materials selectively absorb one or more frequencies of light and transmit what is not absorbed.

So, a red shirt will absorb all colors except red and reflect the red light, so you see the shirt as red.
A red filter will absorb all colors except red, and both reflect red and transmit red light, so you will see the filter as red AND it will let red light go through it - so the leaves will only get the red light.

I hope that helps and you will be able to explain it to your son.

Tonya

stgroulx,

To add onto what Tonya has provided, I think you were also asking about the discrepancy in step 8 that says the leaves will be absorbing the colour of the sleeve. The I've read through the procedures and it is noting that the coloured sleeves will filter all other light out except the one colour frequency. This colour is allowed to transmit through, as Tonya described, to hit the leaf. Instead of blocking that colour. This is different from an uncovered leaf in sunlight that absorbs all frequencies of colour and retransmits a select few (like green) that we see as colour.

Think of it like this. If you have a sponge and you spray it with a song stream of water, most will get absorbed into the body of the sponge, some will be absorbed only enough to interact with the top layer atoms but have enough energy to be reflected back and splash out, and some will soak all the way through and come out the other side. Now unlike my example how light reacts depends on the frequency (colour) of light and the atomic structure of the material be interacted with.