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Colors, Colors, Everywhere

In this post, we are going to spend a bit more time with color--light and pigments.  By now when you hear the words reflect and absorb, each should have new meaning to you. Now what happens when we mix colors from either type?

http://edtech2.boisestate.edu/eckela/images/Light-vs-Pigment2.gif

Have you ever wondered why a stage looks white when all the stage lights are not white?

 

http://www.showproaudio.net/Theatre_Lighting_Large.jpg

Perhaps, you were able to use the color mixing guide for light in the image above this one to answer my question.

Transmission, Reflection, and Absorption
We already know that the color of an opaque object is the color that it reflects. The color of a transparent or translucent object is the color that it transmits. What exactly does this mean? This means that the color of an object depends on the light that shines on the object and the light that that bounces off or is transmitted through the object. 

Look at the two windows below.  The first window (which is transparent) is only transmitting white light because it allows all colors of light to pass through. However, the stained glass handles light a bit differently.  The color of the glass determines what colors will be transmitted through.  In other words, green blades of grass in the stained glass only transmit green light and absorbs all others.  So what colors of light are transmitted through the trophy in the stained window glass? 

http://fiveashrenovations.com/images/window.jpg

This takes us into the topic of color filters. I am sure you have seen color filters one time or another, but what happens when a color filter is placed in front of an object? A couple of things actually occur.  Can you tell from the pictures below what happens? (These pictures should look familiar as they were taken from the textbook.)

The images show the red filter only allows red light waves to transmit or pass through while it absorbs all others. As a result, the red on the apple is reflected and still looks quite red behind the filter.  However, the apple leaves don't appear green behind the filter.  Instead they appear black. You can see what happens when the color filter is changed to green and then blue.  In these cases what colors would be absorbed, transmitted, and reflected?

I guess before I wrap this subject up we should just address two more things. Is there really such a thing as black light? What happens to objects when there is no light?

For question one, check out this informative website.  As far as the second question is concerned, let's revisit the first image on this post.  When you mix any or all of the colors of light, none of the combinations make black light. So why do objects appear black, especially at night?  Well the answer is simple.  Objects appear black because there is an absence of light.  What? That's right! This means that there are no available colors of light reflecting off of the object, therefore, the object will appear to look black.  Remember to see color, the cones and rods in our eyes need to absorb and focus the light waves to determine the colors we see.  Without the light filtering into our eyes, our eyes will not be able to pick up the colors on the object.

Over the last final days of this semester, we will be engaging in light lab activities. You will need to take all that you have learned and connect it to the activities.  Before I wrap up, I spent some time sharing these images created with an iPhone, a prism, and a spectroscope. How about you share what you learned about these items and what they have to do with light with your parents. You can also make your own spectroscope  by following the directions found here.

Created with a spectroscope (The light is focused and then passes through a prism inside the spectroscope.)

Created with an iPhone and an equilateral prism (The objects are located to the sides of the front-facing camera.)

Waves Interference and Standing Waves

Here are some of the items discussed in class this week that I thought I would post.

Do You See What I See?

Said the science teacher do her science class, "Do you see what I see?"

Okay, okay so we probably can't break into chorus right now, but our title does highlight the focus of this post.  We have finished our reading about how the eye sees visible light in terms of different wavelengths.  This post will go in depth about how light interacts with the objects that we see.

First let's get 3 terms out of the way: transparent, translucent, and opaque.

Light Interactions by Monique Prince is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

Objects that are transparent --> glass, window, water bottle, clear wrap
(You are able to see right through the object once light interacts with it.)
Objects that are translucent --> sheer material, wax paper
(You are able to see that something is behind this type of material, but may not always be able to make out every aspect of the object because as the light passes through it is being scattered throughout.)
Objects that are opaque --> suitcase, handbag, construction paper, comforter, desk, school portrait, aluminum foil, concrete)
(These objects either reflect light or absorb it. As stated in last week's post, objects that absorb light energy usually convert that energy to thermal energy)

Are these clouds opaque, translucent, or transparent?

(c) M. Prince, 2012

(c) M. Prince, 2012

Now, how exactly are we able to see the things that we see?

(c) M. Prince, 2012

 Once light shines on an object, our eyes gather and focus the light so that we may be able to see it.  Eyes are able to transmit, refract, and respond to different wavelengths of light.  This small section of light that we can see is visible light.  Our lenses help us to focus on an object. Light is refracted (bent) from an object to the cornea of our eye.  The light then passes through the pupil and the lens. The iris that surrounds our pupil opens and closes to direct the amount of light we take in through our eyes.  Once the light hits the retina at the back of our eyes, it hits the rods and cones which respond to both light and color of the objects   The rods and cones send signals to the option nerve that helps the brain to interpret the images we are seeing.

(c) M. Prince, 2012

The color that we see on the object is the color that is being reflected.  For instance, the eye images are focusing on a tree.  We are able to see the green leaves and the brown trunk because The colors that make up green are being reflected while all other colors are being absorbed. The same is said for the brown we see on the tree trunk.


How do we see the color on many objects?
The electromagnetic spectrum is a wave with many frequencies.  Remember the longer the wavelength, the lower the frequency.  The shorter the wavelength, the higher the frequency.  Now almost in the middle of the electromagnetic spectrum is a very small section of wavelengths that is just the right size for the human eye to see.  This section is called visible light as previously stated.

Colors of Light vs. Colors of Pigments

http://www.diycalculator.com/imgs/console-09.gif

Did you know that your eye can only detect three colors of light? Well, it's true.  Your eye picks up red, green, and blue (see image above).  Your brain helps you mix those three colors to get yellow, magenta, cyan, and of course, white.  The colors that you see on the images in your television screen.  Now every time you see a white image on the TV screen, you will know all the colors that help to make up that image's color.

Now while you may be able to mix all those colors to get white light, I highly do not recommend that you get your paint set and mix all those colors up to get white.  It simply won't work! Pigment colors do not produce the same colors when mixed.  In school, you have been told that your primary colors are red, blue, and yellow also, right? Well, that is not exactly true.  The primary colors of pigment are yellow, cyan, and magenta. Magenta and yellow make up red, while magenta and cyan make up blue.  When you mix all these colors together you get black, which is quite different from colors of light being combined.

This begs the question: How exactly can you create black from the colors of light? The answer to this is quite simple. In order to see black, it requires that absence of light.  Think about it: If you remove all light-producing objects in your room, close your bedroom door and windows, the only thing you will see are black objects. Give it a try!

Here's a website that covers a great deal of information on Light and Color.

Can you answer the questions for last week's post now?
1. What is the color of George Washington's white horse?
2. Why do you suppose we can only see black at night?
3. What is the difference between colors of light and colors of pigment?
4. How does light interact with different materials?

Making Waves Lab

It took the entire week to do this lab. I have some students who volunteered to share their discoveries and understandings from this lab.  Be on the lookout for this upcoming student podcast!

I had a wonderful time sitting down with several groups this week to "listen in" on what they learned about the properties of waves and the relationship between speed, wavelength, and frequency.

Here are a few videos I created on measuring waves that you may find helpful. While doing this lab, we have to find the speed of the wave by calculating the distance of each wave (4m) by the time it took in each trial.  Once we found the speed of each wave, we could then calculate for the frequency, by substituting what we already knew (speed and wavelength) and setting up our formula (frequency = wave speed / wavelength).  The three videos show us how to generally solve for the unknown.

How Do Waves Behave?

Okay folks, we are still covering the information from last week's blog this week.  We wrapped up with characteristics and properties and we are going to jump into wave behavior after completing our lab on wave speed.  Hopefully, I will get a chance to update this post with a few videos, but in the meantime go ahead and look at the FOUR PREDICTABLE WAYS that waves behave:

(c) Prince, 2012

(c) Prince, 2012

(c) Prince, 2012

(c) Prince, 2012

Questions to Consider This Week:
1. What is the color of George Washington's white horse?
2. What do you suppose we can only see objects black at night?
3. What is the difference between colors of light and colors of pigment?
4. How does light react when it interacts with transparent, translucent, and opaque materials?

Making Waves Lab
PQ: How does a wave's speed relate to its frequency and wavelength?

Students completing the first wave and tracing over it before they measure the length of a wave.

Your task is to conduct three trials making and measuring waves to determine the relationship between wave speed, frequency, and wavelength.  As a group, go through the pre-lab discussion.  Collect your materials and begin working on the lab.  Follow the directions exactly how they are provided.  You will need to add a "speed" column to your data table. What happens the the wavelength and the frequency increases or decreases? Were any of your predictions correct?