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.
Hi PF
Are there an interaction between an electromagnetic wave and a charge source? For example, does an electromagnetic wave get attracted by a charge source, the same way the Earth attracts the moon? Or is something else going on?
i really want to understand the lesson so bad i read the lesson 10 times and the lesson is like 50 pages and i still don't get the concept of how electromagnetic waves were originated??
and what about polarization? please with all the details you have and thank you
Homework Statement
A laser beam of power P and diameter D is directed upward at one circular face (of diameter d < D) of a perfectly reflecting cylinder. The cylinder is levitated because the upward radiation force matches the downward gravitational force. If the cylinder's density is ρ...
Hi,
In electromagnetic wave, electric field take the form
E(z,t)=A q(t) sin(kz)
where A is a constant, k is a wave number, and q(t) is a time dependent factor having the dimension of length.
This mean that q is a position..but position of what ??
Is a position of the wave ?
Below is the Wikipedia URL shows the shape of EM wave.
http://upload.wikimedia.org/wikipedia/commons/3/35/Onde_electromagnetique.svg"
Electromagnetic laws say that'
"changing magnetic field produce electric field and changing electric field produce magnetic field"
In the...
Homework Statement
Hi there! I am currently taking physics and we are in the process of learning about electromagnetic radiation. I am a bit confused as to how exactly an electromagnetic wave is produced. I understand that a periodically oscillating charge produces and oscillating magnetic...
Lately I'm thinking about the question of how to convey how Maxwell was able to derive from first principles how fast electromagetic waves propagate. How is that possible at all?In Maxwell's time it was already well known, of course, that the electric field and the magnetic field are very much...
"mass" of electromagnetic waves
Consider the stress energy tensor T^{\mu\nu} of a particle. Integrating the trace T over space gives the invariant mass m of the particle. For electromagnetic fields, T=0 which fits with the quantum picture where a photon has zero invariant mass.
However...
We all know that Earth is rotating. So every particle on it is accelerating. So all the charges present on it are accelerating. So why there is no production of elecrtomagnetic waves by them? (As accelerating charges produce EM waves)
Can I assert that any charged particle vibrating at a certain frequency produces an electromagnetic wave with the same frequency? Considering this, do elastic waves generate electromagnetic waves?
Boundary conditions & time domain electromagnetic waves: does classical model fit?
Consider two propagating media: a lossy dielectric medium and a lossless dielectric medium. Thus, the interface that separates them has two tangential components of electric field, one for each medium. One of...
-Why do electromagnetic waves not readily penetrate metals?
Also a question occurred in class, and they asked
-"The sun emits most of its electromagnetic wave energy in the visible region of the spectrum with the peak in the yellow-green. Our eyes are sensitive to the same range, with peak...
based on this picture
if light is made up of little tiny massless particles called photons
what are radio waves made of?
what are microwaves made of?
what are infrared waves made of?
what are ultraviolet waves made of?
what are x-ray waves made of?
gamma rays are made of electrons and...
I've two electromagnetic waves (light) with amplitudes 1x (normal) and 2x (double) amplitude. And I want to pass these two waves through a "normalizer" expecting 1x amplitude for both waves.
Question is: Is such a "normalizer" possible and/or exists. I'm not looking for any electronic...
I am following Engineering Electromagnetic by H. Hayt,
And there, we derived, the speed of Electromagnetic wave in good copper is just around 3.2m/s.
Sure, this can't mean it takes 1 second for a light bulb 3.2 m away to glow if I press a switch? I have experience that this is almost...
Homework Statement
Not really a homework/coursework problem, I'm just trying to make sense of some class notes from our chapter on special relativity. I'm trying to find the expression for electromagnetic wave propagation in a reference frame S' that is moving at a constant velocity with...
Hello!
Not sure if I've posted here before... (in the intorductory Physics section, that is!)
Anyway, I don't have a particularly good understanding of physics, and I have just started looking at waves recently. However, I have a quick question regarding electromagnetic waves. I have read that...
Homework Statement
Suppose Maxwell's displacement current was left out of the Maxwell equations. Show that , in a vacuum, the magnetic field has to have the form B = grad f(r,t), where f is any function which satisfies the Laplace equation.
Homework Equations
curl E = - dB/dt
curl B = 0...
If we have case \rho=0, \vec{j}=\vec{0}
then we have this equations
\Delta\vec{E}-\frac{1}{c^2}\frac{\partial^2 \vec{E}}{\partial t^2}
\Delta\vec{B}-\frac{1}{c^2}\frac{\partial^2 \vec{B}}{\partial t^2}
Particular solutions of this equation
\vec{E}=\vec{E}_0...
Hello, could you please help to clarifly the following.
Do electromagnetic (e.g. light) and gravitational wavefronts caused by e.g. a supernova both appear at the same time seen from a distant observer perspective?
Thank you!
Homework Statement
Two monocromatic waves is given by
\vec{E_1}=\vec{E}_{01}cos(\vec{k}\cdot\vec{r}-\omega t+\alpha_1) and
\vec{E_2}=\vec{E}_{02}cos(\vec{k}\cdot\vec{r}-\omega t+\alpha_1)
are linearly polarized along two normal directions. Taking that waves have equal amplitude...
Hello. In most texts I have read, EM radiation is depicted as sinusoidal in shape. I understand why this would be the case, as the oscillating fields are often the product of circular generators or alternating current, but is this always the case? For example, is the light we receive from stars...
Homework Statement
Consider a plane-polarised electromagnetic wave in source-free vacuum, with magnetic field B = (1,1,0)BoCos(kz-wt), with Bo = 0.001 Tesla. Find
(1) the direction of propagation of the wave,
(2) average energy density carried by the wave, and
(3) the fraction of this...
Hi,
My doubt is how can the EM waves interact with an electron, i.e.,
electron is a particle with negative charge.. have EM waves any charge to attract or to repulse an electron ? :confused:
An example is the microwaves oven when waves interact with water molecules.
Thanks :smile:
In what direction does the magnetic component of an EM wave oscillate?
Is there a lateral end to the interference pattern created in the double slit experiment, and if so, what defines it?
How fast do EM waves expand laterally?
In the double slit experiment, what makes the interference...
Can anyone tell me what Maxwell said is the source of electromagnetic waves? I read that accelerating charges produce EM waves; are there any other sources?
Homework Statement
1.The magnitude of the electric field between the two circular parallel plates is
E = (4.0 x 105 ) - (6.0 x 104 t), with E in volts per meter and t in seconds. At
t = 0, the field is upward. The plate area is 4.0 x 10-2 m2. For t > 0,
a) what are the magnitude and...
Hi
I've looking into path loss for electromagnetic waves and it's quite straight forward to figure out how it works in free space by looking at the free space path loss formula (http://en.wikipedia.org/wiki/Free-space_path_loss).
It has not been that easy figuring out how another medium...
Until now I've learned that light is electromagnetic waves. I haven't learned about photons yet, but I'm guessing that photons are waves according to the electromagnetism theory (or quantum mechanics?, or both?).
My question is "when do you consider photons as particles"? Particles in the...
Hi,
I come across these 2 questions on a website:
1. Why are the antenna on TV and Radios about the same length
2. Why is the antenna on the cellphone (i.e. the older versions) smaller than the Radio antenna?
My answers to these 2 questions are: Firstly, the waves that the cellphone...
Homework Statement
The electric components E1 and E2 of two coherent electromagnetic waves are given as follows :
E_1=E_o\sin (\omega t-kx)
E_2=E_o\sin (\omega t-k(x+\delta))
These two waves superpose each other at a certain point . Derive the amplitude of the resultant wave in...
There is one thing that’s bugging me.
I read about electromagnetic spectrum. It says that light is, by its nature, electromagnetic wave just like radio signals, microwaves, X and gamma rays, infrared waves etc. The only difference between these waves is their frequency, right?
Now imagine...
I am interested in naturally occurring electromagnetic waves, is there a reference that lists wavelength, frequency, electric and magnetic fields, etc.?
Since the combined speed of electormagnetic waves can be 'c' and that they travel in space at 'c' leaves no component for time, hence the time on a watch on a beam of electromagnetic wave does not change at all.
With this understanding, assume two stationary mobile phone users U1 and U2...
I'm a bit confused, when drawing the diagram for oblique incidence, how do I choose which way to draw the electric field? For example, I know the direction of the wave is in the plane of incidence and the wave vectors are simply arrows in the direction of the wave that I draw - and that the E...
I don't really know how to put my doubt in words but I will try.
Electromagnetis waves of various frequencies are used for
communication.Also there are EM waves from other sources, for
example even sunlight is eloctromagnetic wave.Now all these
waves are out there in space. So at...
I am confused regarding the heat properties of electromagnetic radiation. Wiki states "Any electromagnetic radiation can heat a material when it is absorbed.". Does this imply radiation with wavelengths in the visible light region can also heat a material, that is, increase its temperature? From...
Homework Statement
Given the electromagnetic wave traveling in the y direction at velocity c:
B = +cEo sin(k y − ω t) ˆi.
a) What happens to the ratio of the electric to magnetic field if the angular velocity ω of the
wave is decreased? Does it decrease, increase, or remain the same...
I understand that they come from objects with high temperature. But to me it makes no sense because from what I understand temperature is measuring the small molecules moving around, I do not see where the relationship is between the two. Do I have an idea mixed up?
AC Circuits II: AC Power Generator
Homework Statement
A An AC generator supplies an rms voltage of 110 V at 60.0 Hz. It is connected in series with a 0.300 H inductor, a 5.80 μF capacitor and a 236 Ω resistor.
What is the impedance of the circuit?
B What is the rms current through the...
Homework Statement
The 2.0-cm-diameter solenoid in the figure passes through the center of a 6.0-cm-diameter loop. The magnetic field inside the solenoid is 0.20 T.
What is the magnetic flux through the loop when it is perpendicular to the solenoid?
Φ1 = Wb
What is the magnetic flux...
Hello there my fellow physics fact finders,
As the title suggests, I was wondering if we use infrared and radio waves to communicate information because they're the only waves that can carry information, or just because they're the safest.
Which actually brings me on to another question, how...
Homework Statement
Homework Equations
For a plane polarized electromagnetic wave traveling along the z axis, with its E vector parallel to the x-axis and its H vector parallel to the y axis, Faraday's law
\nabla\times \textbf{E}=-\frac{\partial \textbf{B}}{\partial t}
gives that...