Paramagnetic materials have a small, positive susceptibility to magnetic fields. These materials are slightly attracted by a magnetic field and the material does not retain the magnetic properties when the external field is removed. Paramagnetic properties are due to the presence of some unpaired electrons, and from the realignment of the electron paths caused by the external magnetic field. Paramagnetic materials include magnesium, molybdenum, lithium, and tantalum.
Ferromagnetic materials have a large, positive susceptibility to an external magnetic field. They exhibit a strong attraction to magnetic fields and are able to retain their magnetic properties after the external field has been removed. Ferromagnetic materials have some unpaired electrons so their atoms have a net magnetic moment. They get their strong magnetic properties due to the presence of magnetic domains. In these domains, large numbers of atom’s moments (1012 to 1015) are aligned parallel so that the magnetic force within the domain is strong. When a ferromagnetic material is in the unmagnetized state, the domains are nearly randomly organized and the net magnetic field for the part as a whole is zero. When a magnetizing force is applied, the domains become aligned to produce a strong magnetic field within the part. Iron, nickel, and cobalt are examples of ferromagnetic materials. Components with these materials are commonly inspected using the magnetic particle method.
Diamagnetic materials have a weak, negative susceptibility to magnetic fields. Diamagnetic materials are slightly repelled by a magnetic field and the material does not retain the magnetic properties when the external field is removed. In diamagnetic materials all the electron are paired so there is no permanent net magnetic moment per atom. Diamagnetic properties arise from the realignment of the electron paths under the influence of an external magnetic field. Most elements in the periodic table, including copper, silver, and gold, are diamagnetic.
Light with the shortest wavelengths and the highest energies and frequencies in the electromagnetic spectrum; also called gamma radiation. Gamma rays are produced by violent events such as supernova explosions. They are also produced by the decay of radioactive materials. Gamma rays can kill living cells, so it is good that Earth’s atmosphere can stop them. Gamma radiation is used in medicine to kill cancer cells.
A high-energy stream of electromagnetic radiation having a frequency higher than that of ultraviolet light but less than that of a gamma ray (in the range of approximately 1016 to 1019 hertz). X-rays are absorbed by many forms of matter, including body tissues, and are used in medicine and industry to produce images of internal structures.
Invisible solar radiation that lies just beyond the violet end of the visible spectrum in the wavelength range from 10 to 400 nanometers (just below the x-ray range) and can harm living tissue. Much of the UV radiation is absorbed by the ozone molecules in the upper atmosphere (stratosphere), but a potentially dangerous amount passes through the ozone hole to cause cataracts, skin cancer (melanoma), suppression of the immune system, leaf damage, and reduced yields in some crops. UV rays are generated also during electric (arc) welding.
The visible light spectrum is the section of the electromagnetic radiation spectrum that is visible to the human eye. It ranges in wavelength from approximately 400 nm (4 x 10-7 m) to 700 nm (7 x 10-7 m). It is also known as the optical spectrum of light. The wavelength (which is related to frequency and energy) of the light determines the perceived color. The ranges of these different colors are listed in the table below. Some sources vary these ranges pretty drastically, and the boundaries of them are somewhat approximate as they blend into each other. The edges of the visible light spectrum blend into the ultraviolet and infrared levels of radiation. Most light that we interact with is in the form of white light, which contains many or all of these wavelength ranges within them. Shining white light through a prism causes the wavelengths to bend at slightly different angles due to optical refraction. The resulting light is, therefore, split across the visible color spectrum.
This is what causes a rainbow, with airborne water particles acting as the refractive medium. The order of wavelengths (as shown to the right) is in order of wavelength, which can be remembered by the pneumonic “Roy G. Biv” for Red, Orange, Yellow, Green, Blue, Indigo (the blue/violet border), and Violet. You’ll notice that in the image and table Cyan is also appears fairly distinctly, between green & blue. By using special sources, refractors, and filters, you can get a narrow band of about 10 nm in wavelength that is considered monochromatic light. Lasers are special because they are the most consistent source of narrowly monochromatic light that we can achieve.
Of or relating to the range of invisible radiation wavelengths from about 750 nanometers, just longer than red in the visible spectrum, to 1 millimeter, on the border of the microwave region.
The super-high frequency (SHF) and extremely high frequency (EHF) of microwaves come after radio waves. Microwaves are waves that are typically short enough to employ tubular metal waveguides of reasonable diameter. Microwave energy is produced with klystron and magnetron tubes, and with solid state diodes such as Gunn and IMPATT devices. Microwaves are absorbed by molecules that have a dipole moment in liquids. In a microwave oven, this effect is used to heat food. Low-intensity microwave radiation is used in Wi-Fi, although this is at intensity levels unable to cause thermal heating.
Radio waves have the longest wavelengths in the electromagnetic spectrum. These waves can be longer than a football field or as short as a football. Radio waves do more than just bring music to your radio. They also carry signals for your television and cellular phones.