Making Waves. A vibrating source creates waves. A vibrating electrically charged rod will create a set of electromagnetic waves.

Transcription

1 Making Waves A vibrating source creates waves. A vibrating electrically charged rod will create a set of electromagnetic waves.

2 Making Electromagnetic Waves Actually, any device that runs on alternating current can generate an electromagnetic wave. As the electrons in this antenna move back and forth, they generate ripples in the electric and magnetic fields.

3 Electromagnetic Waves All electromagnetic waves move through space at the speed of light. In a vacuum that is 3.0 x 10 8 m/s.

4 Electromagnetic Spectrum

5 Velocity = Frequency x Wavelength Frequency and wavelength are inversely proportional to each other. If an E-M wave's frequency increases, its wavelength must decrease by the same amount.

6 Electromagnetic Spectrum E-M waves are classified and ranked according to their frequency and wavelength.

7 Selectivity in Nature Substances can either reflect, absorb, or transmit E-M waves that fall upon them. In this example, the glass is opaque to infrared and ultraviolet light, but for visible light it is transparent.

8 Selectivity in Nature White light is actually a mixture of all the frequencies of visible light. The glass selectively bends the different frequencies through different angles, causing the those frequencies or colors to separate from each other.

9 Selectivity in Nature Some substances reflect all the visible frequencies of light that fall upon them. Other substances absorb all those frequencies. The absence of reflected light makes them appear dark.

10 Selectivity in Nature Some substances are even more selective. This surface absorbs all frequencies except for red, which it reflects to our eyes. This surface looks blue because blue is the only frequency of light it reflects.

11 Selectivity in Nature Even transparent objects can be more selective. A blue filter transmits blue light only. The other frequencies are absorbed. A less than perfect filter will let small amounts of the colors it is supposed to absorb pass on through.

12 What is white? We know that all the frequencies (colors) of visible light make white when mixed together. When light falls upon a rough, textured surface, it is scattered in many directions, mixing the colors well. This is especially true for grainy crystalline substances like snow, sugar, and salt. This is why they look white.

13 What is white? Actually, you don't need all of the colors to make white light. Only red, green, and blue are necessary.

14 The Primary Colors of Light That is because the retina of the human eye has receptors for 3 specific wavelengths (colors) of light. They are: red, green, and blue. These are called the additive primary colors.

15 The Primary Colors of Light

16 The Science of Color Mixing Where red and green spotlights overlap, the colors combine to create yellow. But when red and green filters overlap, we get darkness. Why is this so?

17 The Science of Color Mixing No matter whether it's yellow light or the combination of red and green light, the same red & green receptors are stimulated in the retina of the eye. Either way, it's going to look yellow.

18 The Science of Color Mixing The red filter only lets red light through. The green filter would let green light through but the red filter already absorbed it. There is no light that can pass through both filters to reach the eye.

19 Subtractive Color Mixing When you mix paints you think you are adding colors. What you are really doing is taking away light. The pigments in paints and inks act like filters that selectively absorb certain wavelengths (colors) of light.

20 Subtractive Color Mixing Mix enough paint or stack enough filters and eventually you will filter out all the light. The filters shown here represent the three primary colors used in the printing process: cyan, magenta, and yellow.

21 Primary Colors of Pigments Notice that the secondary colors for pigments are identical to the primary colors for light.

22 Rendering Color in Computer Software The computer sends an RGB signal to the monitor but must translate it into a CMYK signal for the printer.

23 Why Is The Sky Blue? Molecules in the atmosphere do a better job of scattering blue light than colors at the other end of the spectrum. The light blue color shows up well against the blackness of space.

24 Thin-film Interference Another way to filter out colors of light is to reflect light off from a thin film.

25 Thin-film Interference Here, light reflects off from a thin film of oil on top of water.

26 Thin-film Interference Here is the same phenomenon as seen in soap bubbles. Different colors get filtered out in different places according to how the thickness of the soap bubble's wall will vary.