## Electromagnetic (EM) radiation is the energy transmitted through space or a material medium in the form of electromagnetic waves. The frequency range of such waves is tremendous, and is shown by the electromagnetic spectrum. These waves include radio waves, microwaves, infrared waves, visible light waves, ultraviolet (UV) waves, X-rays, and gamma rays.

###### 6,782 Questions
Space Travel and Exploration
Energy

# How do thermocouples generate electrical energy?

A thermocouple produces a tiny voltage proportional to the temperature difference between two junctions where dissimilar metals meet.

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Thermocouples use rare-earth metals (chromium, aluminum, nickel, etc), usually in pairs. As these metals heat up, they react with one another and one metal sheds off an electron, which is then seen as electricity. Thermocouples usually produce a very small amount of electricity, often only enough to operate electric 'gates'.

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Physics
Waves Vibrations and Oscillations

# What equation relates frequency and wavelength and speed of light?

(Frequency) x (Wavelength) = Speed of light.

Note carefully that the "speed of light" in the equation above is the speed of light in the medium that the wavelength is measured in. In vacuum it will be the famous constant "c", but when light travels through any sort of material it's speed is slowed and its wavelength shortened by a factor called the refractive index of the medium. Because wavelength and speed are reduced by the same factor the equation still holds. Light's frequency is not affected by the medium.

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Earth Sciences
Electrostatics
Batteries

# Who invented the lemon battery?

alessandro volta

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Electricity and Magnetism
Waves Vibrations and Oscillations

# How electromagnetic wave produced?

electromagnetic waves are produced by the changes in the sub atomic level when heat or electricity is applied to an atom electron which is present in lower energy level will obsorbs energy and jumps in to higher energy level after that it again jumps in to lower energy level.when the electron is jumping in to lower energy level it emitts energy in the form of photons.these transmission of photons is said to be electromagnetic waves.in the electromagnetic waves electric and magnetic fields are perpendicular to each other and also perpendicular to the direction of wave propagation.

EM waves can also be produced by the action of a radio-frequency current in an antenna. Radio transmitters produce power at a single frequency and the antenna acts as a tranducer taking the power from the transmitter and converting it into power that is radiated into space and can be received at a distant point.

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Health
Physics
Pollution

299300301
Science
Physics

# Which mechanism of heat transfer can work in a vacuum?

The radiation of thermal energy can occur in a vacuum. Radiation is accomplished by the movement of electromagnetic waves through the vacuum, like light. Light, and particularly infrared light, is often associated with the movement of thermal energy (heat) through a vacuum.

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Toys
Cooking Equipment

# How does infrared cook food?

IR is heat in the form of electromagnetic radiation. The IR is absorbed by the food causing it to become hotter, eventually becoming cooked (or finally burning).

The Easy-Bake oven toy uses mostly the IR emitted from a 100W lightbulb to bake its small thin "cakes".

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Math and Arithmetic

# How do you find the wave frequency?

You can Stick to the formula which is :

wavelengths/secounds = Hz

so that

Frequency (Hz) = Wave speed (m/s) / Wavelength (m)

OR

Frequency (Hz) = 1 / Period (s)

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Electronics Engineering

AM.

289290291
Chemistry
Electrostatics

# What does electromagnetic spectrum refer to?

The EM spectrum is the range of frequencies of EM radiation.

From low to high frequencies the spectrum goes: Radio, Microwave, Infrared, Visible, Ultraviolet, X-ray, and Gamma ray.

Frequency is inversely related to wavelength by c = frequency * wavelength where c is the speed of light. So the same spectrum goes from long wavelength to short wavelength

289290291
Physics
Chemistry

UV and IR radiation are both electromagnetic radiations. They differ in wavelength (the distance traveled by the wave in the time of one period, which is related to frequency). UV has a shorter wavelength than IR, and is thus more energetic (because shorter wavelength also means higher frequency, and the energy of a single photon is proportional to its frequency.) The energy in each photon in the UV frequency range is enough to wreak havoc with the structures of many moelcules, and thus cause a wide range of damage. This can be damage to tissue (as in a sunburn) or to DNA molecules (causing risk of skin cancer) or something relatively harmless, like the activation of a mechanism in the skin that increases pigmentation (i.e., a suntan.) This is also why the sun has a bleaching effect on the colors of many objects (the UV alters or destroys the molecules that provide the color) and causes others to become weak or brittle.

IR photons, on the other hand, have only enough energy to shake molecules around a little, which makes material hot but doesn't do any real damage (unless there's enough to make it reallyhot.) That's why IR is sometimes erroneously referred to as "heat rays."

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Science
Physics
Visible Light Spectrum

# Who discovered the visible spectrum of light?

Isaac Newton discovered the visible spectrum of light while fooling around with a prism (from which is derived the basic principle of a rainbow.) He later wrote about his findings in his well-known book, Optiks. Isaac Newton was also a master of atsronomy, calculus, and physics. It was also he who "discovered" gravity when an apple fell on his head. It is also probable that this experience led him to discover the effect of concussions on dementia. OK, not really about the dementia part.

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Physics
X-Ray

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Science
Physics

# Would a laser be visible in a vacuum?

It depends on how you mean it. If one is holding a laser and light is shining on it, then of course it can be seen. But I assume you are talking about a laser beam.

For the spot where the beam hits some object, yes the illuminated spot is visible. A vacuum has no real effect on light. A vacuum environment is just an environment that has had all the air (and other material) sucked out of it (and thus all objects regardless of shape and size fall at the same speed, but one digresses) but this vacuum has little effect on light.

On the other hand, if you're talking about seeing the beam itself then the answer is no. Light travels in a straight line unless it's path is effected by some matter. If a laser projects its light in any direction except directly at your eye, none of the light will enter your eye unless something causes its path to change. In air, there is usually some dust, smoke, mist, or some such stuff that scatters a small fraction of the laser light and allows you to see the beam. Even in perfectly clean air, the air itself scatters a very small fraction of the light, so a bright enough beam can be seen. But in a vacuum, there is no material to divert any of the light toward your eye, so you can not see it at all.

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Magnetism

# Who invented the first semiconductor diode what it is called as and from which metal it is made up of?

The first modern semiconductor diode was made with germanium. These diodes were invented in ww2 for RADAR.

But before that semiconductor diodes were made with galena (lead sulfide), copper oxide, and selenium. I have no idea which was "first".

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Electronics Engineering
Physics
Electrical Engineering

By definition, an isotropic radiator radiates equally well in all directions. A simple vertical whip would have such a pattern in the horizontal field.

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Chemistry
Ozone Layer

# Is UV radiation filtered out by the ozone layer?

Yes, the ozone layer filters out all the UV-C (the most dangerous ultra-violet radiation) and most of the UV-B. The least dangerous radiation is UV-A, and most of this reaches the surface of the earth.

More detail:

Oxygen and nitrogen are the primary absorbers of UV-C and more energetic light (X-rays, gamma rays from space), and they do this completely by the lower stratosphere. One side effect of their absorption of this light, is they make ozone. This ozone is concentrated here, since it is unstable, and the "ozone layer" is formed. Some recombines into N2O*, which later forms either ozone or more stable NOx (if it encounters water vapor first). Some single oxygen atoms encounter O2 and make ozone directly.

Ozone absorbs UV light shorter than 260 nm or so. This includes UV-B, UV-C and more energetic light. Only ozone in our atmosphere absorbs UV-B, which would otherwise be stopped only by soil, meters depth of water, or the DNA of all surface life on Earth.

Additionally, the natural and Man-made "greenhouse gases" in our atmosphere (carbon dioxide, water vapor, ozone, for examples), serve to allow visible light and UV-A in to Earth's surface, but moderate the transmission of infrared light back to space... keeping Earth a tad bit warmer than it would otherwise be without an atmosphere.

Long wave UV (UV-A) and visible light always gets through the ozone layer. As the ozone layer is thinned, additional energetic UV (UV-B) gets through, which will cause problems down here on the surface.

As UV is absorbed, and used in a reaction O3 + uv light = O + O2 ,

Ozone directly absorbs UV-B and either becomes oxygen, or becomes ozone again, with the light scattered again in random directions.

When UV hits the Ozone (O3) it is 'absorbed,' meaning the energy is used to split the ozone into Oxygen gas (O2) and an Oxygen free radical (O). The remaining energy from the UV light is re-emitted as infra-red (heat).

O3 + UV-B -> O2 + O

The Ozone layer is situated on the upper stratosphere. Ozone (O3) is very unstable gas. Ozone is the only gas in our atmosphere that absorbs UV-B.

Oxygen and nitrogen molecules absorb UV-C and more energetic light, and later recombine in different forms. Oxygen atoms sometimes recombine to form ozone, and this primarily occurs in the lower stratosphere... and forms the ozone layer.

Oxygen and nitrogen protect us from very short wave UV, by absorbing the light and breaking apart.

Similarly, ozone has an extra resonance (than its parent oxygen), and can absorb less energetic UV, stuff that still causes cancer, and ozone breaks apart into oxygen gas and a oxygen atom looking for a place to land.

Infrared radiation such as the sun which is blocked by the ozone layer. Such as why to much time in the sun will give you skin cancer. Also it reminds you of when you go to the dentist, whoever is taking your x-ray never stays in the same room and that is why they put a huge metal pad over you. If they did not, it might give them cancer.

Oxygen and nitrogen absorb UV-C. Some of the "shattered" oxygen forms ozone. The UV-C mostly ends up as both heat, and re-emitted as less energetic light in a random direction.

Ozone absorbs UV-B (and some UV-C). The UV-B mostly ends up as heat, and re-emitted as less energetic light in a random direction. Some of the ozone is destroyed in the process of absorbing UV-C or UV-B, and little of it reforms as ozone.

Since atmospheric gases have very low absorptivity / emissivity at visible and IR wavelengths, they do not contribute to heating the surface of the Earth to any great extent. Ozone does have some limited resonance in the IR range, which is why it is called a greenhouse gas too. But it has very low concentration.

UV- C is filtered out but UV-A and UV-B however are not. UV-B is the radiation which begins oxidization of your skin and UV-A is the rays in which change the pigmentation of your skin togive you a tan, UV-C is the only extremely harmful rays and the ozone layer does in fact block them out.

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# Does violet have the shortest wavelength?

Yes, out of all the colors of visible light, violet has the shortest wavelength.

217218219
Physics

# What is the quality factor of gamma rays?

Gamma rays have a quality factor of about one.

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Nuclear Physics
Physics

# What is the difference between bremsstrahlung and characteristic radiation?

Bremstrahlung is German for "braking radiation." It refers to radiation that is associated with the positive or negative acceleration of charged particles. The energy of the emitted photon equals the loss of kinetic energy of the particle. Characteristic radiation refers to groups of discrete wavelengths characteristic of the emitting element.

215216217
Science
Physics

# An acrostic for the em spectrum?

GaXrUlViInMiRa. Done by the first two letters of each type of wavelength. The visible spectrum really consist of the colors but here is listed as "Vi."

Gallant X-rays ultimately violate interesting micron radios.

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Science
Physics
X-Ray

# Sunscreen is used to protect the skin from exposure to which type of solar radiation Visible X-rays Infrared Ultraviolet Microwaves?

Sunscreen is used to protect the skin from ultraviolet radiation emitted primarily by our sun. The ozone layer also protects us from ultraviolet rays, however the current problems with holes in the ozone layer makes wearing sunscreen almost essential if one is going to be outside for an extended period of time.

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Laser Tag

# What is spiking in ruby laser?

The emission of laser beam through the semitransparent end face actually consists of spikes of high intensity emissions. This phenomen is called spiking of the laser.

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Medical Technologies
X-Ray

# Which sorts of materials are transparent to x-rays?

X rays are are able to penetrate less dense materials easily, such as muscle and skin tissue in medical situations or plastics and wood in other applications.

As the material becomes more dense, the x rays penetrate less easily.

Materials such as steel or bone in a medical setting are more dense along with such materials as lead and tungsten in engineering situations.

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Cosmology
Nuclear Physics
Thermodynamics and Statistical Mechanics

# What are the best physics project topics?

The best physics project topics to study depends on what you find interesting.

If you find everyday things like motion, pendulums, and collisions interesting, study mechanics.

If you find things like optics, circuits, and electricity interesting, study electromagnetism.

If you find things like statistics, temperature, and entropy interesting, study thermodynamics.

If you find things like time dilation, the speed of light, and black holes interesting, study relativity.

If you find things like the universe, dark matter, and star formation interesting, study cosmology, astrophysics, and nuclear physics.

If you find things like particles, accelerators, atomic bombs and unified force theories interesting, first study quantum mechanics, then study nuclear and particle physics.

If you meant what are the best physics project topics to do as a science experiment, use the guidelines I stated above, but stick to the first three topics; mechanics, electromagnetism, and thermodynamics.

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