Electromagnetic Radiation

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
Cooking Equipment
Electromagnetic Radiation

Who invented the microwave cooker?

Percy LeBaron Spencer is regarded as the inventor of the microwave oven. Spencer worked as an engineer with the Raytheon company, which was a company that developed defence and industrial equipment. The story goes that the concept of the microwave was discovered by accident while Spencer was experimenting with and testing a magnetron (diode vacuum tube).

The magnetron, which had been invented during WWII at Manchester University, produced microwaves of such high frequency and power that it was invaluable in directing allied aircraft to intercept German Luftwaffe raiders during the battle of Britain.

The magnetron was passed to Raytheon in the USA for further development. During testing, Dr Spencer reached into his pocket for his chocolate bar and discovered it had completely melted. He noted the connection between the melted chocolate and the heat-producing magnetron, and tested his theory on a bag of unpopped corn kernels, which then popped. In further testing, he placed an egg in front of the magnetron, and the egg exploded.

For this reason, Spencer is credited with discovering one of the critical components of the microwave oven. Further modifications of the microwave oven developed out of his observations, and by 1947 Raytheon had perfected a commercial microwave oven. It was a large unit about the size of a tall cupboard and remained large until the Apollo 11 astronauts returned to Earth and were immediately quarantined in a sealed caravan in case they had brought Moon bacteria back to Earth. They cooked their meals on one of the first counter top Microwave ovens ever made.

The first magnetron was invented by Randall and Boot at Bournemouth University in 1940. Due to the exigencies of war, this invention like many others was suppressed from public knowledge at the time.

Electromagnetic Radiation

What part of EM spectrum does the arecibo telescope detect?


Electromagnetic Radiation
Earth Day

What would happen if electricity in the world ran out?

since the world is full of electronics, when the world ran out of electricity, machines that are dependent to electricity won't work (like computers, TV, etc.),machines that have their own battery won't work too because batteries have electricity (like PSP,nintendo ds, laptop, etc.), transportation won't work because they have batteries, batteries have electricity (like cars, motorcycles, the subway) back to basic.. the uses of animals for transportation, no high-tech entertainment, no movies, no night life, early bedtime, early mornings.

Electromagnetic Radiation
Visible Light Spectrum

What is the difference between Free Electron Theory and Band Theory of solids?

Free Electron Theory:

This theory tells that, metals conduct electricity because of the presence of free electrons in it. The outermost shells of metal atoms will be loosely bound with their nucleus. So the electrons in it are free to move anywhere in the solid.These electrons are called free electrons and they are responsible for the conduction of electricity.

Band theory of solids:

A solid is assumed to contain many bands in which the electrons in it are packed. The most important are valence band and conduction band. The energy of electrons in these bands will be different.The difference in energies of valence band and conduction band determines whether the solid is a conductor, semi - conductor or insulator.For insulators, the difference between energies of them ( energy gap ) will be very high, and for conductor, these bands overlap each other.

The conduction band carries the electrons that conduct electricity, but the valence band has all the electrons in the ground state. Whether they go into the conduction band depends on the temperature and the energy gap between the bands. In a conductor, these bands overlap, and hence many electrons can become conducting. Thus, Band Theory explains distinction between metals and insulators, which Free Electron theory cannot do (since it assumes all valence electrons become conducting). Calculations are be performed to see which materials will have big energy gaps and which will have overlapping bands.

Electricity and Magnetism
Electromagnetic Radiation

What is the wavelength of water?

Water absorbs over a wide range of electromagnetic radiation with rotational transitions and intermolecular vibrations responsible for absorption in the microwave (≈ 1 mm - 10 cm wavelength) and far-infrared (≈ 10 µm - 1 mm), intramolecular vibrational transitions in the infrared (≈ 1 µ- 10 µ) and electronic .


Electromagnetic Radiation

What is spatial aberration?

Spatial aberration is a term used in optics that means how blurry something is.

Electromagnetic Radiation

What Far field approximation gives?

if we're talking about a short dipole, you have {E.H} field depending by r^(-k), where r is distance between antenna's feed and point of {E,H} calculus and k is >=1.

In far field, you can imagine r>>1, so r^(-k) contribution is lower for greater k and you can approximate {E,H} expression by considering only the contribution with the lowest k.

This make Poynting vector become real, according with the assumption that far field radiation power is active, near field one has also a capacitive contribution.

Electromagnetic Radiation

What are the negative effects of overexposure to radiation?

DNA Damage.

Electromagnetic Radiation
Ozone Layer

What does nm in calculation of ultraviolet rays mean?

nm = nanometers

It is a measure of the wavelength of the light, with energy inversely proportional to the wavelength: E = h / wavelength

Electricity and Magnetism
Electromagnetic Radiation
Waves Vibrations and Oscillations

Why is light considered as electromagnetic wave?

James Maxwell was able to show that a vibrating charge would result in the propagation of an electromagnetic wave that would travel with velocity that "just happened" to be the speed of light. Since that time, repeated tests have shown that every prediction resulting from the idea that radio waves, light waves, and x-rays (amongst others) are examples of this EM wave have turned out to be correct.

Light is considered to be an EM wave because every test of that statement has given a positive answer.

That is, until, quantum theorists were able to show that light travels in discrete chunks of energy now called "photons."

Environmental Issues
Electromagnetic Radiation

What are radiative corrections in high energy physics?

Radiative corrections are higher-order corrections to leading order feynman diagrams. i.e. accounting for loop contributions.

Electromagnetic Radiation

What type of wave could measure 5 meters in length?


Electromagnetic Radiation

Is there any infrared radiation at night?

yes, the earth radiates heat as IR into space and gets cooler at night.

Consumer Electronics
Mobile Phones
Electromagnetic Radiation

What is the amount of radiation output by a portable device?

Well it depends on the device but anyway it is very little. Cellphones have the highest emission and you shouldn't keep them close like a pocket especially if you are pregnant as it is said it could probably make birth defieciencies.

Electromagnetic Radiation
Air Pollution
Ozone Layer

Does Ozone in the ozone layer absorbs infrared radiation from the Sun?

yes it does

Electromagnetic Radiation
Visible Light Spectrum

How much energy does Uv Light Visible Light and X-Rays have?

X-ray energies in the range 120 eV to 120 keV. UV energies from 3eV to 124 eV.

General and Special Relativity
Electromagnetic Radiation

What is the difference between a concave and a convex lens?

Convex lenses are thicker in the middle than at the edges. They refract toward the center. Only people have convex lenses. Concave lenses are used in telescopes and glasses. Concave lenses are thinner in the middle than at the edges. When light passes through concave lenses always bend away from each other toward the edges of the lens.
A convex or "positive" lens is thicker in the middle and thinner at the edges. A concave, or "negative" lens is thinner at the middle and thicker at the edges. Convex lenses project a real image behind the lens; concave lenses project a virtual image in front of the lens.

Electromagnetic Radiation
Solar Flares

Does solar radiation contain a complete spectrum of all forms of electromagnetic radiation?

Yes it does. It contains all the forms of radiation, but 99% of its energy is carried by radiation with wavelengths between 278 and 4600 nm, with the maximum at 4720 nm.

Pregnancy Health and Safety (Prenatal Care)
Fetal Development
Electromagnetic Radiation

Is it true that radiation on airplanes could harm a fetus?

as a flight attendant, we have the highest amount of miscarriages in any industry. my book on becoming pregnant tells 3 different times how hard it is to become pregnant while flying a lot in the airplane. after being off work for 2 months, i just now became pregnant, and i know this info is in the pilots association web site. our union wont print the radiation chart for the f/a s to see. if you know a pilot, ask him to print it up, you wouldn't believe how much radiation is up there on a plane. im going to find a pilot friend, and ask him to do this, will get back to you with more statistics. t


this web site has good information and the risk is very very very....... small for the occasional flyer. the radiation is typical cosmic radiation the kind you get from just stepping outside on a sunny day.the closer you get to the sun the greater the radiation. read the site

Electromagnetic Radiation

What is the difference in relative frequency between red and violet light?

Violet light has a higher frequency than red light by roughly a factor of 2.

Earth Sciences
Electromagnetic Radiation

Where is infared-waves type of radiation located on the electromagnetic spectrum in relation to other kinds of radiation?

low frequency radio

high frequency radio including microwave


here --> . . . . . infrared . . . . .

red light

orange light

yellow light

green light

blue light

violet light

ultraviolet radiation


gamma rays

cosmic rays

Electromagnetic Radiation
Waves Vibrations and Oscillations

What are the 7 types of electromagnetic waves in order?

radio wave 30cm>

microwave 1nm-30cm

infrared 700nm-1nm

visible light 400nm-700nm the only wave that can be seen by human eyes

ultraviolet 60nm-400nm

x rays 0.001nm-60nm

gamma rays >0.1nm

Electromagnetic Radiation
Waves Vibrations and Oscillations

What electromagnetic wave shows heat loss in buildings?

Infrared radiation

Electromagnetic Radiation

Is lenz law used to find induced EMF's?

It's primary usage is to determine the nature of an induced EMF from changes in the magnetic flux through a circuit. However, you must use Faraday's Law (and a unit conversion factor) to determine the SIZE of such an EMF.

Electricity and Magnetism
Electromagnetic Radiation

Electric energy can be converted into?

Electric energy can be converted into many things, all of them are other forms of energy. Electric energy can be converted into heat energy, like in many stoves and ovens. Electric energy can be converted into sound energy, which happens in speakers. Electric energy can be converted into mechanical energy, like with electric motors in fans and other devices. Electric energy can be converted into light energy as with a light bulb.

Unfortunately, we do not currently have the technology to turn energy forms into matter as is shown in many sci-fi shows like Star Trek's replicators.

Every energy is able to change its type. For example sound energy can be converted into electrical , light, heat and in many other forms.


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