What is Electromagnetic waves: Definition and 329 Discussions
In physics, electromagnetic radiation (EM radiation or EMR) refers to the waves (or their quanta, photons) of the electromagnetic field, propagating through space, carrying electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays. All of these waves form part of the electromagnetic spectrum.Classically, electromagnetic radiation consists of electromagnetic waves, which are synchronized oscillations of electric and magnetic fields. Electromagnetic radiation or electromagnetic waves are created due to periodic change of electric or magnetic field. Depending on how this periodic change occurs and the power generated, different wavelengths of electromagnetic spectrum are produced. In a vacuum, electromagnetic waves travel at the speed of light, commonly denoted c. In homogeneous, isotropic media, the oscillations of the two fields are perpendicular to each other and perpendicular to the direction of energy and wave propagation, forming a transverse wave. The wavefront of electromagnetic waves emitted from a point source (such as a light bulb) is a sphere. The position of an electromagnetic wave within the electromagnetic spectrum can be characterized by either its frequency of oscillation or its wavelength. Electromagnetic waves of different frequency are called by different names since they have different sources and effects on matter. In order of increasing frequency and decreasing wavelength these are: radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.Electromagnetic waves are emitted by electrically charged particles undergoing acceleration, and these waves can subsequently interact with other charged particles, exerting force on them. EM waves carry energy, momentum and angular momentum away from their source particle and can impart those quantities to matter with which they interact. Electromagnetic radiation is associated with those EM waves that are free to propagate themselves ("radiate") without the continuing influence of the moving charges that produced them, because they have achieved sufficient distance from those charges. Thus, EMR is sometimes referred to as the far field. In this language, the near field refers to EM fields near the charges and current that directly produced them, specifically electromagnetic induction and electrostatic induction phenomena.
In quantum mechanics, an alternate way of viewing EMR is that it consists of photons, uncharged elementary particles with zero rest mass which are the quanta of the electromagnetic field, responsible for all electromagnetic interactions. Quantum electrodynamics is the theory of how EMR interacts with matter on an atomic level. Quantum effects provide additional sources of EMR, such as the transition of electrons to lower energy levels in an atom and black-body radiation. The energy of an individual photon is quantized and is greater for photons of higher frequency. This relationship is given by Planck's equation E = hf, where E is the energy per photon, f is the frequency of the photon, and h is Planck's constant. A single gamma ray photon, for example, might carry ~100,000 times the energy of a single photon of visible light.
The effects of EMR upon chemical compounds and biological organisms depend both upon the radiation's power and its frequency. EMR of visible or lower frequencies (i.e., visible light, infrared, microwaves, and radio waves) is called non-ionizing radiation, because its photons do not individually have enough energy to ionize atoms or molecules or break chemical bonds. The effects of these radiations on chemical systems and living tissue are caused primarily by heating effects from the combined energy transfer of many photons. In contrast, high frequency ultraviolet, X-rays and gamma rays are called ionizing radiation, since individual photons of such high frequency have enough energy to ionize molecules or break chemical bonds. These radiations have the ability to cause chemical reactions and damage living cells beyond that resulting from simple heating, and can be a health hazard.
We can determine what kind of elements exist in different planets by observing electromagnetic waves from planets' direction, but does anyone have any suggestion on how planets generate electromagnetic waves at the first place?
Does anyone have any suggestions?
Thanks in advance for any...
Yer.. I'm lazy and tired, did not enough research and found out that the radio/electromagnetic wave makes all the electrons move back and forth when the wave oscillates between the magnetic and electric fields... so you can see how much the current oscillates etc.
But... um cameras work...
Homework Statement
In what units is energy density measured?
1. Watts
2. Watts per cubic meter
3. Newtons per meter
4. Joules per cubic meter
Homework Equations
E = cB (as derived by Maxwell)
The Attempt at a Solution
This question is so basic yet I'm confused. I thought...
This is a question about electromagnetic waves and gravitational waves.
Let's say we're on the Earth and we're looking up at the sun (safely).
If the sun were --for some reason-- to violently and dramatically jerk from its position, how would we first find out?
Would we first *see* the...
My book takes a look at the maxwell equations in free space, shows that E and B satisfies the wave equation and then guesses on a plane wave as a solution such that you get a tranverse wave with E and B perpendicular to the direction of propagation.
I don't know if I am too slow in realizing...
I was watching the lectures on the MIT OCW course 5.111 where it was said that electromagnetic radiations are periodic variations of the electric field. Does it mean that when we are talking about electromagnetic radiation, frequency indicates how quickly do the electric fields change(their...
I am trying to figure out how I would go about finding the steady-state temperature distribution in an absorbing medium using the steady-state heat conduction equation:
(1) -\nabla\cdot\left(K\nabla T\right) = q_{gen}
where T is the material's temperature, K is the material's thermal...
Ive asked this question so many times on various forums and i feel there is a simple answer that i just haven't heard yet. I realize that an EM wave is represented as a sine wave, but from what i understand, that's not the physical motion the fields take. Let's say we take a snapshot at the peak...
I have seen the retarded potentials and what not, but what has always bothered me is why these field solutions reflect when they meet surfaces.
I have looked and looked, but there seem to be no analytical explanations for this, only empirical ones.
So my gripe is, since electromagnetic waves...
Let's say I have some source that generates a spherical wave that propagates outwards at the speed of light, and I have a vehicle that is charged.
The wave will accelerate my vehicle periodically and eventually bring it to great speeds.
Does this work?
I know they're represented as sine waves but what would they actually look like in space. they wouldn't actually physically go up and down and side to side like a sine wave would they? I have seen representations of sound waves, which i assume is a longitudinal wave, but not a EM wave.
Why does nickel reflect infrared, but gold does not?
I've seen devices that shine infrared at a metal surface and measure the reflectance. They're mainly used for looking at thin film coatings.
For example, you could have a metal part made of nickel, and thinly coated in gold. The gold...
Every book I ever read describes a electromagnetic wave as a phenomena generated by charged particles accelerating. This will produce a change in electric field that induces a magnetic field.
But, due to Maxwell equations a change in magnetic field will also produce an electric field. So, if a...
This is just a conceptual question that I've been personally wondering about. So light has a magnetic field wave perpendicular to an electric field wave. I don't quite understand the magnetic field wave though.
I thought that magnetic fields were not supposed to have a beginning or end. They...
Let's suppose that on Earth I have two devices which permits me to detect the gravitation produced and electromagnetic waves (photons) emitted by the Sun. Then, the Sun suddenly disappears. Which of the two devices will notice first that the Sun has gone, i.e. which wave propagates faster, the...
Homework Statement
The figure below shows a plane electromagnetic sinusoidal wave propagating in the x direction. Suppose the wavelength is 56.0 m and the electric field vibrates in the xy plane with an amplitude of 20.0 V/m.
(a) Calculate the frequency of the wave.
(b) Calculate the magnetic...
I haven't been able to find any literature that answers this question in a pleasing way. Also, all sources on the internet are contradictory.
If electromagnetic waves (out of phase since they are emitted by the gaseous atoms in discharge tube) sent through a diffraction gitter interfered with...
I was just thinking about electromagnetic fields and magnetostatics. Magnetostatics is the study of magnetic fields where they do not change or very little. I was wondering if a static magnetic field is still considered part of a Electromagnetic field? Since the magnetic field is not changing...
I am having trouble understanding how a light wave travels through a medium, such as the Earth's atmosphere when emitted from a light bulb...
I have read some topics on the difference between transverse and longitudinal waves, but I am having trouble understanding how they exist.
I can imagine...
I have trouble understanding the concept of electromagnetic waves.
my textbook has the following explanation for electromagnetic momentum. It's not very clear to me.
[ light reflecting from a perfect reflector will leave the surface with its initial momentum, thus having twice its initial...
So what i understand from my professor about the electromagnetic waves is this :
an electric charge has an electric field E
a moving electric charge induces a magnetic field B
The electromagnetic wave produced is due to the moving charge which has both components E and B...
But my...
Hi
There is lots of text, but it is actually just a presentation of facts and thoughts to explain where I am in all this.
There are two main questions:
1) Are the incident waves from a very distant source, say a star very far away, interfering with one another to create one or more resulting...
Hello, why the electromagnetic waves move up and down instead of just travel straight?
When an electron go in a lower energy level it relases a photon, but where does this photon came from?
Thank you!
Homework Statement
A plane monochromatic electromagnetic wave with wavelength λ = 2.2 cm, propagates through a vacuum. Its magnetic field is described by
\vec{B} = (Bx\vec{i} + By\vec{j})cos(kz+ωt)
where Bx = 1.8E-6 T and By = 3.8E-6 T, and i-hat and j-hat are the unit vectors in the +x and...
I hope this is the right forum for a first year undergraduate problem!
The problem I've been working on is here: http://i.imgur.com/IhTtL.png
I think that I have the correct answers, but I'm not sure. I think that the energy densities of the E and B field components will be (0.5)(ε0)(E^2)...
Hi
Much of what I am going to write in this post is based on what I have read and understood (with very, very limited knowledge of the subject) on the Internet. So, if I have been misinformed or I have misunderstood anything, please don't hesitate to correct me. I would appreciate it.
As...
I like to know if electromagnetic waves pass through a medium (Glass) and if this medium were in contact with two other mediums in its boundary which the first one with same optical dense (Glass) and the second with less optical dense (air).
Is there any tendency or priority for wave to pass...
I've always thought that photons and electromagnetic waves are one in the same. And I still do, but I'm trying to get a better grasp on the idea and am finding it difficult.
1) As I understand it, they are the same. But an electromagnetic wave with definite frequency is a perfect sine wave...
Hi all,
I'm trying to understand exactly what the physical meaning of conductivity/current is in relation to waves.
if we have a wave traveling through a conductor, we find that it decays exponentially, i.e.
e^{-\alpha z}
where \alpha=imag(k)=\omega\sqrt{\frac{\epsilon\mu}{2}}...
Hi everyone I have a question that has been bothering me for a while now. I have basically built a Faraday cage using wire mesh. I know there is a relationship between the mesh hole size and the wave suppressing ability of the cage.
As I understand it an electromagnetic wave can be thought of...
Homework Statement
Hi
In Griffiths it is stated that any possible wave can be written as a sum of plane waves
f(z,t)=\int_{-\infty}^{\infty}{A(k)e^{i(kz-\omega t)}dk}
This is a sum over spatial frequencies. In another book I have, they write the H-field as
H(r, t) = \sum_n{C_n H_n(r)\exp...
You know how a microwave oven has a mesh on the door so visible light gets through but not the microwaves? Can such a thing be done with infrared radiation too? Is it possible to block heat from getting through a mesh but not visible light?
Both are energy right?
I'm asking cause I'm trying to understand the double-slit experiment and I'm just wondering how they can be sure to treat the electron as a particle. Could it be performed with for instance whole atoms or maybe the cores or something else that's more obviously matter...
Say one had three intense laser pulses and one weak reference pulse coming together on the surface of a thin nonlinear medium as if coming from the corners of a square. The three intense laser pulses mix, and there will be the third order mixing k1+k2-k3 or k1-k2+k3 or whatever coming out in the...
I'm having some trouble understanding visually the propagation of an electromagnetic wave. I'm self-studying electrodynamics so I've never had someone explain this properly to me.
I understand an electromagnetic wave is a propagating disturbance in an electromagnetic field. Originally, I...
Are the amplitudes of the electric and magnetic components of an electromagnetic wave proportional?
Or is the amplitude of the electric portion unrelated to that of the magnetic portion?
Homework Statement
Electromagnetic waves contain time varying electric and magnetic field perpendicular to each other and also to path of progression. The phase difference between electric field vector and magnetic field vector is zero
Homework Equations
The Attempt at a Solution...
A standing wave can be produced in a guitar string where the wavelength of the wave is the same length as the string (I believe this is referred to as the first harmonic) and where the string is an exact multiple of the wavelength of the wave (referred to as the second and subsequent harmonics)...
Hello,
This is not homework, as I'm not in school :)
I was wondering if there are any standard equations for electromagnetic waves interfering with each other. For instance, can I change the frequency of a wave by hitting it with another wave of a different frequency? I can find info on...
From: http://answers.yahoo.com/question/index?qid=20090223155307AAgqbWk
Question: Why are electromagnetic waves transverse waves?
Answer: "Because they are generated by the rapid vibration of elecrons, which go side to side, perpendicular to the direction the waves travel (very very rapid...
Hey everyone,
Im doing this research and reading this http://science.hq.nasa.gov/kids/imagers/ems/gamma.html" it had a diagram of the depth of penetration of different wavelengths into the eaths atmosphere...
my question is, How come x-rays penetrate deeper than visible light - what is the...
If EM waves are pumped into a resonant cavity at it's resonant frequency will each incoming wave add it's energy to amplify the wave(s) in the cavity?
I know that if you pulse a light source into a circular wave guide and you pulse the light source each time the light wave returns to it's...
Hello every one .
We know Radio waves carrying data
When a radio device receives radio waves , It render the waves and we hear sound .
Now my questions are :
1 - How data on electromagnetic waves are transmitted ?
When a electromagnetic wave hit a atom it absorbed by the atom
like this...
Electromagnetic waves, aka light and such. What is it?. I know that it is a wave of energy, magnetic and electric forces traveling in wave forms but when struck turning into a particle. But what exactly are they made of? Is it just a pure wave of energy and nothing else to it?
Do physicists...
Hi guys,
I am too old to remember basic knowledge about electromagnetic waves :D
I am looking for a combination of an electromagnetic wave and a material such that the wave can pass through human tissues, but it is blocked by the material. All I know is that X-ray/gamma can penetrate human...
In the double slit experiment, a wave is forced to go through a tiny slit. I do not understand what is stopping it from going through the barrier.
After all, we can think of an electromagnetic wave as just the electric/magnetic fields of a sinusoidally oscillating particle, evaluated using...
Homework Statement
The average intensity of sunlight at the top of the Earth's atmosphere is about 1400 W/m^2. What is the maximum energy that a 20 m × 30 m solar panel could collect in one hour in this sunlight?
Homework Equations
Not sure what equation to use
The Attempt...