electromagnetics ???

[seanguyen]

Does anyone in here has great skill or knowledge of electromagnetics (including waves, fields, and its appllications)?
I would love to know and discuss more about it. I want to improve my skill, knowledge and my thought of it in communication in the complex media.

[yeudoi]

Uses in Rail roads. Medical scans, motors, generator, car lifting, finding gold :15:, surgery, loud speakers...

Someone please give some thery on this would be nice. All I can remember now is
F = BIL sin(theta)

[roro]

:) cái này có nhiều applications, quá trời rộng không biet phai start tù đâu :) Roro củng 0 good lám, nhó đuọc có chút

dzị thủ start from def. for Electromagnetics:
It is the study of the effects of electric charges at rest or in motion. Its applications: thinking of radio, phone (mobile phone), satellite, radar, microwave ovens, enegry conversion (motors, generators) ...

Electromagnetic theory is no more abstract than circuit theorỵ
In circuit theory, main system variables are Voltages and currents, and they are constants (for d-c circuit), time dependent (for ac circuits). They are scalar quantities and independent of space coordinates.

But in Electromagnetic, most often encounter vectors, quantities have both magnitude and direction. And electromagnetic variables are function of time as well as of space coordinantes

(F=BILsin(theta)), just remember được tí ti from that equation :
for ex: a metal bar sliding over the railroad with constant velocity, v, in a static magnetic field B, there is a force Fm = q v X B cause the electrons freely moving in a bar to drift toward the end of the conductor and leaved the other end of positive charged, which create a seperation of positive and negative charges. That force is known as the Coloumbian force of attraction and the magetic force Fm that carries current I in magnetic B is
Fm = integral (Idl x B) (the limit is the distance of the railroad or close contour)

again B is the vector, which has the magnitude and direction, with the cross product, it has angle (direction)

Roro củng nhó có chút ít, but like to discuss about this topic , Anyone know more about this please share

[Chris-T]

I like to know more & learn about this subject. But I have none or
very limitted understanding about it, thus cannot share with you.
It's very interesting subject and are widely used/applied nowadays
for commercial uses. Thanks for bringing it up.:)

[seanguyen]

Thank you (yeudoi, roro, Chris T) so much to join with me on this topic.
To other viewers, always welcome to drop a few lines.

I agree that this topic is so broad to define and of course there are so many of its applications in real life. Let's start with the basic understand (without equations or formulas). What is electromagnetics? (Việt Nam gọi là điện không gian) Can anyone give a speech of it so people who have no knowledge about it still understand what it is? That's why I said above "without equation"?
What the difference between regular circuit theory and electromagnetic theory? (Sự khác biệt giữa điện gia dụng và điện không gian?)

Electromagnetic is much more complex than the circuit that we learn in circuit theory class or circuit at home. One thing we need to know when talking about the electromagnetic is frequency. In circuit theory, the frequency is 60 Hz or below, sometime we assume it's equal to zero. In other hand, frequency in electromagnetic is very high.

Talk later

[Tuong-Vi]

gosh this topic is so Broad and to be able to just define electromagnetics is quite difficult in itself because one has to have some idea of fundemental physics to be able to grasp the basic understanding of forces, and laws that lie within the definition...

here's my definition of Electromagnetics

there are two important dynamic effect in electromagnetics , one is the generation of electric fields by time-varying magnetic fields, as expressed by Faraday's law. Another is the complementary effect whereby time-varying electric fields produce magnetic fields.

It is said that changing the magnetic flux density produces a change in electric fields and/or vice versa; and this leads the production of electromagnetic waves. In general, wave phenomena result when there are two forms of energy, and the presence of a change in one leads to a change of another. If we change the magnetic field at one position, this generates a change of electric field in both time and space, by Faraday's law. The subsequent change of the electric field produces a change of magnetic field through the displacement current, and so on. In energy terms, the energy interchanges between electric and magnetic types as the wave progresses.

Electromagnetic waves exist in nature in the radiation that takes place when atoms or molecules change from one energy state to a lower one, with frequencies from the microwave through visible into x-ray regions of the spectrum. (Still lower frequencies are generated by lightning and other natural fluctuation.) These natural radiations are utilized in astronomy and radio astronomy. Telecommunications, navigational guidance, radar, and power transmission depend on our ability to generate, guide, store, radiate, receive, and detect electromagnetic waves.

[roro]

wowo, supper wa' dzi. be' tv, be' ho.c mo^n to^?ng ho*p. huh,
roro imre dzo go'c ngoi^` ho.c hoi? be' bbx
=============================================

The electromagnetic spectrum is just a name gave by scientists for a several types of radiation when they talk about them as a group.

Electromagnetic spectrum are ranging from the extremely low frequency waves(ELF) to the highest frequency x-rays and gamma rays(which exceed 10^(24) Hz) according to their wave-length.

There are 7 basic types of Electromagnetic Wave (EM): radio waves, microwaves, Infra Red, Visible lights, Ultra Violet, X-rays and Gamma Rays.

Electromagnetic waves generate electric fields as well as magnetic fields.

Electric fields are easily shielded by nonconducting materials while magnetic fields are more difficult to avoid as they can penetrate most substances as all living tissues.

All electromagnetic waves have these properties:

+ are produced when atoms or electrons lose energy
+ are transverse waves
+ transfering energy as vibrating electric and magnetic fields
+ can travel through a vacuum, transfer enery from one place to another
+ travel at a speed of 3x108 m/s in a vacuum (in air this is virtually the same)
+ can be reflected, refracted, diffracted
+ The shorter the wavelength (the higher the frequency) the more dangerous they are

These properties of these waves changes as the frequency changes.

Some definition and some application for wavelength classification:

- Extreme Low Frequency (ELF) : use to detect of burried metal objects
- Supper Low Frequency (SLF) : electric power, submarine
communication
- Ultra Low Frequency (ULF) : Telephone range
- Very Low Frequency (VLF) : Navigation
- Low Frequency (LF) :
- Medium Frequency (MF) : AM radio
- High Frequency (HF) : fascimilie,
- Very high Frequency (VHF) : Television, FM(Frequency Modulated
signal) radio, mobile radio
- Micro-waves : cook food, and sattelite transmission
( the frequency use for cook food: absorb by water molecules)
- Ultra High Frequency (UHF) : Television, radar...
- Supper High Frequency(SHF) : radar, sattelite
- Extremely High Freq. (EHF) : radar, space exploration
- Infra-Red (IR) : night vision
- Ultraviolet (UV)
- X-rays : medical applications
- Gamma rays : food irradiation, cancer therapy

[CAptain DaLaZBoi]

wowo

dzu*~ do^.i a`

Anh roro bi. tuongvi chuong va(ng dzo go'c ngo^`i ru`i hihihi

:)

[roro]

uh, cap. she du~ do^.i thiet., ra chu*o*?ng 1 cai', bay ma^'t tieu luon

[Tuong-Vi]

hhahah chưởng rồi ngu gì ngồi ở đó lảnh đạn roro... người ta chui vô chuồng khò a'... tv học mon tùm lum.. giờ không biết cái gì ra cái gì, sợ tẩu hoả nhap ma á ... roro khiêm nhường kia ta ơi tv học hỏi roro thì có..

ok to be continue with this topic later, giờ phải đi hành hạ học sinh tiếp rồi :D :D khoái job này ghe :D

[Huyenthoai99]

step by step..
In a simple form:

Electrooooomagnetics is composed of electric (E) and magnetic (B) waves, they are always perpendicular to each other

[BungRieu]

Thanks các Anh Chị ...:55:
This sounds interesting ... for BR at K11&K12 ...:p ...
are they independently exist as E-wave and H-wave ???
why do they have to normal to each other ??? :a8: ...any exception ???
Anh Huyenthoai99:. What is the next step ..???. . :a11:

Anh roro : BR was taught that the E-field can be insulated by conducting material ...as in the case of the Faraday cage ...???

PS: NHỮNG CÂU HỎI NÀY KÔ FẢI CỦA MỘT MÌNH BR ĐÂU À NGHEN .:flower2:
BR VÀ MÍ NHỎ BẠN (NGOẠI QUỐC) ARE INTERESTED SO MUCH IN THIS DISCUSSION ...

[roro]

á, mấy questions này, mấy năm truớc quên hỏi ong thầy :D

bungrieu, roro cũng biết chút thui, and has limited understanding about this subject, đang học hỏi à, để try nhe,

+ E-wave, and H-wave: In time varying situation:
E fields and B fields are coupled, and time varying magnetic field gives rise to an electric field
H_wave is related to B and they are all related by Maxwell' s equations
so, they are not independently exist

+ The direction of E-field crossed into the direction of H-field to give the the direction of wave propagation, so they have to normal. The 3 directions (x,y,z component) are mutually perpendicular.

+ yup, good point, thanks bungrieu
The Faraday Cage Effect : means that the electric charge on a conductor sits on the outer surface of it. Therefore, no electrostatic field is present within the conductor

[BungRieu]

Thanks Anh for the explanations ....:55:
We (BR and school friends) are heard about ElectroMagnetic ,
Electrostatic and Magnetostatic ...
Can Anh or someone else give Us some indication about why those classification ??? :a8:
what are the differences between them ..???

[wolf]

I'm not that great in E-mag course, to me it's one of the tough courses in ee field. To understand very well in applied electromagnetism you should have taken some courses such as Multi-D (three dimension), complex algebra 'cos from the begin to end of the course you'd see all the complex equations :D like complex vectors.

As everyone mentioned above that four important fundamental theory of electromagnetic fields are: Faraday's law, Ampere's law, magnetic Gauss' law and electric Gauss' law.

Sean, it's great to hear you love e-mag :D i took this class couple yrs ago and seemed didn't like it even i've taken all the prerequisite courses :D. Theory of Electromagnetic must be a tougher course, have you taken it?

:15:

[roro]

- Electrostatic : the interactions between electric charges that are at rest
- Magnetostatic: (steady magnetic fields) deals with stationary currents, charges moving with constant speeds, and the interaction between these currents

[BungRieu]

Thanks ANh Roro ...:55:..

Còn nữa ..BR có nghe Electrodynamic ... :flower2:
What is that all about ....???

BR thich physics lắm ... chắc sang năm tới nữa ..
chọn ngành này quá ... :p ...

Lúc đó sẽ hỏi mấy Anh Chị đã luôn ... :D ... bây giờ chưa biết hỏi mấy .. :p
Chuẩn bị đi là vừa nghen .... :D ...

[seanguyen]

wolf,
well, I did take a few courses about electromagnetic. But you know, this thing is a abstract topic (I mean "trừu tượng"), and I don't have a change to get hand on and do some real pratical things. You know, talking about waves, seems like we have to close the eyes and try to imagine what it actually looks like. Since we cannot see how it looks like, it's tough to recognize. Agree that electromagnetic stuff can be applied to most of the things in our real word, it's broad!
Tranmission lines, waveguide, cavity are things that we always mentioned about electromagnetics.
The reason that I brought up this topic is I try to understand in Vietnam (because I'm better in my own language) and try to collect (whatever or whoever comes up) all ideas. Assume that I have no knowledge about this thing, and you try to explain to me what it is, how it works, how it looks like, point to something and say "there's some related between this and electromagnetic" and explain it
For example: the cellphone, how it work, you know, blah blah, waves get transfer to this to that .... blah blah.

Electromagnetic is fun, I didn't do much about it, except that I have designed some stripline, microstripline with meet all requirements such as impedance matching, bandwidth, cutoff frequency, source terminator, load terminator.
What I take now is the electromagnetic "stuff" in complex media such plasma. In this range, some of good conductors would have properties of good dielectrics. And, you know, up to this point, the waves are not simple anymore but instead, they are all in 3 dimension, all kind of p waves and s waves mixed, all kind of other factors such size of medium, shape of it, different material (and of course with different properties). Moreover, all scalar constant such as permeability, conductivity, permittiivity are vector now, not scalar anymore.
This thing is tough and I try to catch up with it without a single physical evidence :)