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Chapter 4. The Electromagnetic Spectrum Part 2. Radio waves. Includes FM, AM, radar and TV waves Used in many devices such as remote control items, cell phones, wireless devices, etc. Microwaves.
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Chapter 4 The Electromagnetic Spectrum Part 2
Radio waves • Includes FM, AM, radar and TV waves • Used in many devices such as remote control items, cell phones, wireless devices, etc.
Microwaves • First used in radar, now used in communication (wireless LAN networks), and consumer use (microwave ovens). • medical applications in cancer treatment (destroy tumors by heating them). • Most radio astronomy uses microwaves • “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, in this case, 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 breaks -- when it passes through a prism or raindrops, resulting in the colors we see in a rainbow. • Light also bends ever so slightly due to gravity, when it passes by a planet.
Previous attempts at achieving invisibility have involved bending or reflecting light around the object that is meant to vanish. • The mantle cloak takes a new approach. • Light is a wave that can be disturbed. That's what the mantle cloak does.
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 radiation is popularly known as "heat" Used in heat lamps, de-icing systems and thermomedic therapy. Missile guidance systems, short range communication systems Weather satellites Infrared Waves
Visible Light • The portion of the electromagnetic spectrum that human eyes can detect • ROY G BIV (red, orange, yellow, green, blue, indigo, violet) • Red is the lowest frequency and violet is the highest frequency
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 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.
Homework • Chapter 4: Worksheet 2
