Announcement

Long Exam on Monday for Camia and Jasmine. Tuesday for Sampaguita.

Coverage:
1. Nature of light - please include the reading assignment about the different scientist who measured the speed of light
2. Electromagnetic Spectrum - its components and applications
3. Colors and Pigments

please Schedule your consultation this week before the exam if you think you really need a follow-up on the above topics.

Good luck for your 1st long exam.

exercise: colors and pigments

Physics 1

Exercise #2

1. Two lights are arranged above a white sheet of paper. When the lights are turned on they illuminate the entire sheet of paper (as seen in the diagram below). Each light bulb emits a primary color of light - red (R), green (G), and blue (B). Depending on which primary color of light is used, the paper will appear a different color. Express your understanding of color addition by determining the color that the sheet of paper will appear in the diagrams below.

2. If magenta light and yellow light are added together, will white light be produced? Explain.

3. Blue jeans appear blue because the jeans are permeated by a chemical dye. Explain the role of the dye. That is, what does the dye do (absorb or reflect) to the various frequencies of white light?

4. A red shirt looks red when visible light ("ROYGBIV") shines upon it. Use your physics understanding to explain this phenomenon.

5. In the diagrams below, several sheets of paper are illuminated by different primary colors of light (R for red, B for blue, and G for green). Indicate what primary colors of light will be reflected and the appearance of the sheet of paper. (Note the similarity between this problem and the above problem.)

Nature of Light

History and Properties of Light:

·         Sir Isaac Newton:

§  separates white light to different colors

§  Corpuscular Theory of Light – light as particles

§  Newton’s rings which is a disparity of his particle theory

·         Christian Huygens:

§  Supporter of wave theory

§  Wave fronts are made up of tinier wave fronts

·         Thomas Young:

§  Proponent of wave theory of light

§  Proved that light is a wave by his double slit experiment

·         Albert Einstein:

§  Photoelectric effect

§  Light is made up of photons whose energy is dependent on the frequency

§  Energy is quantized

·         James Clark Maxwell:

§  Light is a vibration of electric and magnetic field which are perpendicular to each other

§  Light is a form of electromagnetic wave with a speed of 3 x 10⁸ m/s

·         Quantum Theory of Light:

§  Light has a dual property but will not occur simultaneously.

§  Light behaves as particle when interacting with matter but will behave as a wave during its travel.

o   Electromagnetic  Spectrum:

As you can see in the figure, we have a decreasing trend in wavelength from radio to gamma ray. Since wavelength is inversely proportional to frequency, it’s the opposite trend in terms of frequency. Visible light is only a small part of EM spectrum which composes seven colors from red to violet.

-all the components will exhibit reflection, refraction, diffraction and interference

- will travel without a medium at a speed of 3 x 10⁸ m/s

- will obey the wave equation v = wavelength x frequency

COLORS & PIGMENTS

Primary Colors of Light: will produce white light when combined

1.       Red

2.       Green

3.       Blue

Light addition is the concept behind colored TV screen. When two of the primary colors are combined, it will produce another color. The set of different colors produced are the secondary colors of light.

COLOR ADDITION

-          Combining colors of light will produce another different color.

Red + Green = Yellow

Green + Blue = Cyan

Red + Blue = Magenta

Complimentary Colors of Light

-          Any two colors of light that when mixed together in equal intensities produce white.

Ex: red and cyan; applying color addition:

Red + Cyan = Red + (Green + Blue) = Red + Green + Blue = White

-          One primary color and 1 secondary color

-          Opposite position on the color wheel

Primary Colors of Pigments: when combined together, it becomes black

1.       Cyan

2.       Magenta

3.       Yellow

When any of the two pigments are combined, it produces different color. The colors produced are the secondary colors of pigment.

1.       Cyan + Magenta = Purple

2.       Magenta + Yellow = Orange

3.       Yellow + Cyan = Green

-          Pigments absorb some of the incident light and reflecting some of it to produces color of the object. It follows color subtraction.

Ex: Yellow pigment: yellow as the secondary color of light is produced by combining red and green, so it absorbs blue. Using color subtraction:

White – Yellow = Red+ Green + Blue – Blue = Red + Green = Yellow.

-          Meaning, it becomes yellow because the light used is white light. It absorbs the blue and reflected the red and green light which makes it yellow. But in the case that the light used is green, the pigment now will become green because of the only color present. Since, yellow pigment cannot absorb green, it is being reflected. In short, the color of an object depends on the source of light used and the type of primary color/s it reflected.

Reading Assignment:

Read on the application of the following:

1.       Scattering Effect

2.       Selective Transmission

3.       Selective Reflection