DAY 161

Video lecture for today https://youtu.be/kf9J6HEJXQc

Goals:  SWBAT 

1. combine colors to remove (absorb) unwanted colors

2. solve color subtraction problems via algebra equations

WARM-UP (3min)

write a sentence explaining how the combination of the magenta and yellow filters creates red light.

Hint: You can use the colored filters simulator from yesterday to answer the above question LINK

CLASSWORK

1. 161A: Color Subtraction

Read the following: 

The previous lesson focused on the principles of color addition. These principles govern the perceived color resulting from the mixing of different colors of light. Principles of color addition have important applications to color television, color computer monitors and on-stage lighting at the theaters. Each of these applications involves the mixing or addition of colors of light to produce a desired appearance. Our understanding of color perception would not be complete without an understanding of the principles of color subtraction. In this part of Lesson 2, we will learn how materials that have been permeated by specific pigments will selectively absorb specific frequencies of light in order to produce a desired appearance.

We have already learned that materials contain atoms that are capable of selectively absorbing one or more frequencies of light. Consider a shirt made of a material that is capable of absorbing blue light. Such a material will absorb blue light (if blue light shines upon it) and reflect the other frequencies of the visible spectrum. What appearance will such a shirt have if illuminated with white light and how can we account for its appearance? To answer this question (and any other similar question), we will rely on our understanding of the three primary colors of light (red, green and blue) and the three secondary colors of light (magenta, yellow and cyan).

 

The Process of Color Subtraction

To begin, consider white light to consist of the three primary colors of light - red, green and blue. If white light is shining on a shirt, then red, green and blue light is shining on the shirt. If the shirt absorbs blue light, then only red and green light will be reflected from the shirt. So while red, green and blue light shine upon the shirt, only red and green light will reflect from it. Red and green light striking your eye always gives the appearance of yellow; for this reason, the shirt will appear yellow. This discussion illustrates the process of color subtraction. In this process, the ultimate color appearance of an object is determined by beginning with a single color or mixture of colors and identifying which color or colors of light are subtracted from the original set. The process is depicted visually by diagram at the right. Furthermore, the process is depicted in terms of an equation in the space below.

W - B = (R + G + B) - B = R + G = Y

Now suppose that cyan light is shining on the same shirt - a shirt made of a material that is capable of absorbing blue light. What appearance will such a shirt have if illuminated with cyan light and how can we account for its appearance? To answer this question, the process of color subtraction will be applied once more. In this situation, we begin with only blue and green primary colors of light (recall that cyan light consists of blue and green light). From this mixture, we must subtract blue light. After the subtractive process, only green light remains. Thus, the shirt will appear green in the presence of cyan light. Observe the representation of this by the diagram at the right and the equation below.

C - B = (G + B) - B = G

 

From these two examples, we can conclude that a shirt that looks yellow when white light shines upon it will look green when cyan light shines upon it. This confuses many 

students of physics, especially those who still believe that the color of a shirt is in the shirt itself. This is the misconception that was targeted earlier in Lesson 2 as we discussed how visible light interacts with matter to produce color. In that part of Lesson 2, it was emphasized that the color of an object does not reside in the object itself. Rather, the color is in the light that shines upon the object and that ultimately becomes reflected or transmitted to our eyes. Extending this conception of color to the above two scenarios, we would reason that the shirt appears yellow if there is some red and green light shining upon it. Yellow light is a combination of red and green light. A shirt appears yellow if it reflects red and green light to our eyes. In order to reflect red and green light, these two primary colors of light must be present in the incident light.

To create colors, printers and artists use three main colors of paint to remove (absorb) unwanted colors. 

Consider a cyan filter - which colors does it allow to pass? Which color will it absorb?

Example 1:

Example 2: Magenta light shines on a sheet of paper containing a yellow pigment. Determine the appearance of the paper.

Example 3: Yellow light shines on a sheet of paper containing a red pigment. Determine the appearance of the paper.

Example 4: Yellow light shines on a sheet of paper containing a blue pigment. Determine the appearance of the paper.

2. 161B: Primary Colors of Paint

A trip to the local newspaper or film developing company will reveal these same principles of color subtraction at work. The three primary colors of paint used by an artist, color printer or film developer are cyan (C), magenta (M), and yellow (Y)

Each primary color of paint absorbs one primary color of light. The color absorbed by a primary color of paint is the complementary color of that paint. The three colors that are primary to an artist (magenta, cyan, and yellow) subtract red, green, and blue individually from an otherwise white sheet of paper. Thus,

Magenta paints absorb green light.

Cyan paints absorb red light.

Yellow paints absorb blue light.

Let's suppose that an artist wishes to use the three primary colors of paint in order to produce a picture of the colorful bird shown at the right. The bird will be painted onto white paper and viewed under white light. It is hoped that the bird will have green tail feathers, a blue lower body, a cyan upper body, a red head, a magenta eye patch, a yellow eye and middle feathers, and a black beak. How can the three primary colors of paint be used to produce such a likeness? And how can we explain the answers in terms of color subtraction?

green tail feathers, Example: apply C & Y

a blue lower body, apply _______ M & C

a cyan upper body, apply ______ C

a red head, ________ M & Y

a magenta eye patch, _______ M

a yellow eye and middle feathers, ________ Y

and a black beak, ________ ALLLLLLLLLLLLL

3. 161C: Applications of Color Subtraction:

Guidelines are on Schoology

Activity is here: LINK

Unable to access today's CW assignment?  Here's the link:

161A,B: https://docs.google.com/document/d/1Zaa934NwL9argye68qr-DRv6n52ACqx3Z3fJqdaDU-8/edit?usp=sharing

161C: https://docs.google.com/document/d/1-F_Ra4whg80iG6zSlvQdnbLH40H55ZWTMQkAFeXWWsg/edit?usp=sharing 

ESSENTIAL QUESTION: How can we build a motor out of magnets, wire, and a battery?

Goals: SWBAT...

1. create successful parallel and series circuits

2. use a voltmeter to measure voltage potential

3. discover the difference between series and parallel circuits

WARM-UP (5min)

1. Answer "pre lab" questions 1-4 (assignment is on Schoology)

CLASSWORK

1. 161A: Circuit Simulation Lab

Lab / instructions are on Schoology. Complete in class today - if you need more time, the hard due date is Sunday 11:59pm

Some clarifications:

Link to simulator: LINK

Can't access the lab for today on schoology? Here's a backup link (LINK)

LEARNING AT HOME (HW)

1. 161B: Check to see what you know about circuits so far: Formative Assessment is on Schoology

2. 161C: Video on Resistance LINK (answer the questions on Schoology, and submit there. Questions are also listed in the following link, in case you can't access Schoology --> LINK)

3. 161D: Final Review LINK (this is mostly complete, but I will be adding thermodynamics content tomorrow)

4. Lab 161A due Sunday 11:59pm

SENIORS: Bring your textbook on Tuesday for return to the bookroom