Light and the Electromagnetic Spectrum

WAVES AND MEDIUMS What medium is light transferred through? LIGHT DOES NOT NEED ONE!

Visible Light Spectrum

Light Light is the form of energy visible to the human eye. This is “radiated by moving charged particles.” *Source: www.centralsquareschools.org/brewerton/artwork/prism.html

Visible light is the smallest part of the electromagnetic spectrum.

LIGHT Light provides the energy need for both plant and animal life. The plants will then complete the process of photosynthesis.

LIGHT The colors of the visible spectrum change depending on the wave frequency.

The higher the frequency the shorter the wave length is. (see chart) LIGHT The higher the frequency the shorter the wave length is. (see chart)

WAVELENGTH AND ENERGY OF THE VISIBLE SPECTRUM COLORS Red 700 nm 1.771 eV Reddish orange 650 nm 1.909 eV Orange 600 nm 2.067 eV Yellow 580 nm 2.138 eV Yellowish green 550 nm 2.254 eV Green 500 nm 2.480 eV Blue 450 nm 2.765 eV Violet 400 nm 3.100 eV Source: Kurt Nassau, Experimenting with Color

It is no coincidence that this wavelength falls within the range of wavelengths at which the Sun emits most of its electromagnetic energy—our eyes have evolved to take greatest advantage of the available light.

Color “Is a physical phenomenon of light or visual perception associated with the various wavelengths in the visible portion of the electromagnetic spectrum.”

COLOR When looking at objects the object appears a certain color. This is the color that is being reflected off of the object, in reality, the object is every color but the color it appears to be.

COLOR White light is made when the primary colors are added together “at equal intensities.”

When all wavelengths of light are being absorbed we see black (black also, isn’t really a color)

The colors we see in objects are the colors that are reflected, all other colors are absorbed. A red t-shirt appears red because red is reflected to our eyes and the other colors are absorbed. When all colors are being reflected we see white light (white isn’t really a color)

Color Reflection So if we see something as WHITE, that means … It reflected back all the wavelengths of light to our eyes If we see something as RED or BLUE It reflected only the RED or only the BLUE wavelengths The others were absorbed. And if we see something as black? It did not reflect back any of the light. © 2003 Mike Maloney

Primary Colors of Light Red Blue Green

Colors of Light These colors can be combined in different proportions to create all other colors.

Secondary Colors of Light Red Light + Green Light = Yellow Blue Light + Green Light = Cyan Blue Light + Red Light = Magenta

Colors of the Spectrum Remember R-O-Y G. B-I-V? Red Orange Yellow Green Blue Indigo Violet

Visible Light We know that the light waves enter our eye, and stimulate parts of it that cause a electrical impulse to be sent to the brain which creates this visual image. But everything does not emit radiation. How do we see those things? And why cant we see a window? © 2003 Mike Maloney

How Do Our Eyes See Color? Two types of cells in the eyes: Rods – Black and white Cones – Color – 3 different types of cone cells - Set 1 – Sees red - Set 2 – Sees blue - Set 3 – Sees green

Our Eyes © 2003 Mike Maloney

LIGHT IS A WAVE! Since light is a wave, it will act like a wave! Interference Reflection – bounce back Refraction – bending through a medium Dispersion - scattering Diffraction – bending to fit through Polarization - concentration

Seeing things We know that when waves run into a boundary they are partially transmitted and partially reflected. Light behaves as a wave, so it to is reflected. Therefore, an object does not need to emit photons itself to be seen, it just has to reflect light back to our eyes where we can detect it. © 2003 Mike Maloney

Objects that do not allow light to pass through them are called opaque. Objects that allow light to pass through them are considered transparent. Objects in between are called translucent.

What is a Prism?

Prisms A Prism is triangular object that separates white light into the spectrum colors. The white light is bent once it enters the prism, and the prism bends the different wavelengths of the white light. Out come the colors of the spectrum. The longer the wavelength (red) the less that it is bent, the shorter the wavelength (violet) the greater it is bent. Prisms are used for many different things: Spectra Scopes and Binoculars. Isaac Newton was the first to show that “When a second prism brings the different colors together again, white light is once more obtained.” Source: http://www.phy6.org/stargaze/Sun4spec.htm

Polarization Polarization is a phenomenon of light that is used in sun-glasses and 3-D movies. Play with the two polarizing filters for a few minutes and note what is happening and see if you can think of any reasons for it. © 2003 Mike Maloney

Polarization Hint Light vibrates in all directions. A polarizing filter acts like a picket fence. It only lets certain direction vibrations pass through it. Therefore, if you pass light through two of them you can completely block the light from passing through. HOW? © 2003 Mike Maloney

Polarization © 2003 Mike Maloney

Color Transmission Filters work in a similar way. Red filters only let RED light thru. Blue let only BLUE light thru. What do you think that UV sticker means on your sunglasses? Why do they sell those orange glasses that are supposed to reduce glare? © 2003 Mike Maloney

Station 1 Prisms

Station 2 What do your eyes see? Reflected or Absorbed

Station 3 Seeing is believing

Station 4 Illusions

Station 5 The rose

Station 6 Color Wheel

Station 7 Venn Diagrams

Station 8 Polarized filters

Station 9 Transparent, Translucent, Opaque

Some Sweet Color Tricks Combining colors in art class How does color printing work? Combining lights Why is the sky blue? Why are sunsets red? Why is water greenish-blue? How does 3-D work? Why does a CD reflect a rainbow, and a mirror does not? How can you help people who are color blind? OTHERS  link to site © 2003 Mike Maloney

BACK © 2003 Mike Maloney

Illuminance Flux is the total of all the light that is emitted from a source. This is not very useful, often we would like to know how much of that light is hitting a surface at some point. The illumination of a surface is called illuminance, E. It is measured in lumens per square meter, lm/m2 © 2003 Mike Maloney

Refraction and Reflection Telescopes Refracting telescopes were the first telescopes ever used. It is said that two children invented this kind of telescope, when they were playing with two lenses. This was perfected by Galileo. Isaac Newton created the Reflecting Telescope. Both telescopes work in the same way. The difference is that reflecting telescopes make better use of mirrors instead of lenses. Refraction Reflection Source: The Universe

Hubble Telescope The Hubble Space Telescope uses refection to portray images. When light enters the telescope it is reflected off of large mirrors that are kept in static, dust free environments. Any dirt or dust present would ruin the images collected. Then the light passes to a secondary mirror which reflects the light to the center of the primary mirror. At the focal point (where the light is focused into one point) the light is set to several different sensors which collect data based on that light. Hubble Space Telescope's “mirrors are made of glass and coated with layers of pure aluminum (three-millionths of an inch thick) and magnesium fluoride (one-millionth of an inch thick) to make them reflect visible, infra-red and ultraviolet light.” The mirror can weight almost 2000 pounds. Source: http://www.howtodostuff.com/hubble

Examples of Visible Light Source: The Universe, and www.nasa.org

C = λν The frequency (v) of a wave is the number of waves to cross a point in 1 second (units are Hertz – cycles/sec or sec-1) λ is the wavelength- the distance from crest to crest on a wave

Why does this make sense? The product of wavelength and frequency always equals the speed of light. C = λν Why does this make sense? NOTE: c is a constant value= 3.00 x 108 m/s

A certain frequency has to be achieved or the effect does not work The photoelectric effect – When light shines on metals, electrons (photoelectrons) are ejected from their surface. A certain frequency has to be achieved or the effect does not work Red light will not cause electrons to eject!

The photoelectric effect has practical applications in photoelectrical cells used for solar powered cars, and solar powered calculators.