The Electromagnetic Spectrum Part 2 Chapter 4 The Electromagnetic Spectrum Part 2

Radio waves Includes FM, AM, and TV waves Used in many devices such as remote control items, cell phones, wireless devices, etc.

Radio Astronomy

Microwaves First used in radar, now used in communication (wireless local internet networks), and consumer use (microwave ovens). medical applications in cancer treatment (destroy tumors by heating them). “Active Denial System” – the “Pain Ray”

The Cloak of Invisibility Physicists in Texas have developed a method to make objects "invisible" within a limited range of light waves. It's not Harry Potter's invisibility cloak just yet, but scientists say it has a lot of potential.

The Cloak of Invisibility Light and invisibility We see things because light reflects off of them and hits our eyes. Or radar (microwaves) bounce off of them and hit a detection device. Light has properties that can be manipulated, which is how objects can be rendered invisible. It can be reflected away, for example. Illusionists can use mirrors to make an object disappear.

Light also refracts -- or bends -- when it passes through an object such as a prism or raindrops, resulting in the colors we see in a rainbow.

Previous attempts at achieving invisibility have involved refracting (bending) or reflecting light around the object so as to make it appear to vanish. The invisibility cloak takes a new approach. It attempts to disturb the light beams so as to neutralize them.

The cloak's material The cloak is made by combining copper tape with polycarbonate, a material commonly used in DVD's and CDs. The resulting cloak has a tiny pattern that neutralizes the waves bouncing off of it.

For it to work, the material's pattern has to be roughly the size of the wavelength of light to be canceled out. Unfortunately that only allows it to work on a limited range of wavelengths.

Current technology allows the cloak to work with only microwaves but scientists say the principle behind the cloak can also be used for visible light.

So far it has only been able to hide objects from the human eye that are so tiny that we can't see them anyway. However, scientists believe that this could "pave the way" for larger objects to be rendered “invisible”.

Infrared Waves Infrared radiation is popularly known as "heat“ Used in heat lamps de-icing systems thermomedic therapy.

Infrared Waves Missile guidance systems, short range communication systems

Infrared Radiation can be detected with special devices such as night goggles

Weather satellites track weather systems using infrared.

Visible Light The portion of the electromagnetic spectrum that human eyes can detect ROY G BIV (red, orange, yellow, green, blue, indigo, violet). Why can we only see the visible light portion of the spectrum?

Visible Light The Sun is the dominant source for visible-light waves our eyes receive. Our Sun produces more yellow light than any other color because its surface temperature is 5,500°C. If the Sun's surface were cooler—say 3,000°C—it would look reddish, like the star Betelgeuse. If the Sun were hotter—say, 12,000°C—it would look blue, like the star Rigel.

Why do the colors of the stars correspond to their temperatures?

We perceive electromagnetic energy having Visible Spectrum We perceive electromagnetic energy having wavelengths in the range 400-700 nm as visible light.

Ultraviolet Can cause skin cancer and blindness in humans Used in tanning beds and sterilizing equipment UV watermarks UV identification

Bee vision is very different from human vision, they perceive colors we are simply incapable of seeing. Most insects have light sensitive cells, or photoreceptors, that are sensitive to ultraviolet light.

X-Rays Primarily used in medicine.

X-Ray Scanners

X-Ray Diffraction The diffraction of X-rays is used to disperse X-rays in a spectrometer and to determine the structure of crystals or molecules.

Gamma rays Highest energy and most dangerous type of radiation. Can cause cancer through damage to DNA. Blocked from Earth’s surface by atmosphere. Used in medicine and irradiation.

Irradiation

Gamma Knife

Electromagnetic Waves

Star Finder Video: Electromagnetic Spectrum (Stop at 4:28)

Homework Chapter 4: Worksheet 2 (due Monday).