What is Excitation: Definition and 142 Discussions

An electric generator or electric motor consists of a rotor spinning in a magnetic field. The magnetic field may be produced by permanent magnets or by field coils. In the case of a machine with field coils, a current must flow in the coils to generate the field, otherwise no power is transferred to or from the rotor. The process of generating a magnetic field by means of an electric current is called excitation. Field coils yield the most flexible form of magnetic flux regulation and de-regulation, but at the expense of a flow of electric current. Hybrid topologies exist, which incorporate both permanent magnets and field coils in the same configuration. The flexible excitation of a rotating electrical machine is employed by either brushless excitation techniques or by the injection of current by carbon brushes (static excitation).

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1. Square wave excitation for lock in amplifier?

Why does square wave for both excitation and demodulation lead to demodulation at DC While using one of the signals sine the signal gets demodulated to odd harmonics? I'm unable to do the maths of Fourier expansion and multiplying and passing through low pass filter

3. B Can an electron remain in an exited state forever with constant energy input?

what will happend if I keep giving the same amount of energy, constant in time to an electron? Will it stay at the exited state forever
4. A How do we derive the number of string excitation modes for large N?

On page 52 in Becker, Becker, Schwarz, there is an equation (2.148) for the number of open string excitation modes. I tried to Tayler expand eq 2.145, but couldn't reproduce 2.148. Plus, one gets 2.145 by setting w close to 1; even if I use the 2.146 and try to analyze it around 0, I am still...
5. I Is a phonon a quasiparticle or a collective excitation?

The Blog Post The Wikipedia Article
6. Very High Standard Deviation in Excitation Emission Matrix Measurement

Hi, I obtain really high standard deviations in Excitation-Emission Spectra mainly for the phenolic compounds in olive oil (Em: 290-350nm). Method: I weigh 0.05g of olive oil and dilute it up to 25ml with cyclohexane to remain in the range of linearity for absorbance measurements to correct...
7. A Coil excitation adjustment on 3D Ansys Maxwell transient analysis

Hi. I am making a 3D Ansys Maxwell project to design DC electromagnet. My model as in attached pictures. I have couple of questions. 1- How important the width value of sheet of coil terminal? Altough I did not change number of conductors and current of coil, changing the width of sheet of the...
8. Synchronous generator variable speed and constant excitation

The question is regarding an electrically excited synchronous generator. Consider that this generator is not connected to the grid and thus not locked with the grid frequency. This generator is spinning at variable speed and gets constant and similar excitation current meaning that the...
9. B Is a photon an excitation of the electromagnetic field?

Allow me to hijack this thread for a second: a photon is an excitation of the electromagnetic field, right? The photon does not exist until measured. So how can we send a photon in a particular direction, so it has a known position and momentum?
10. I Does vacuum excitation violate the conservation of energy?

Hi, there. I am reading the article Relativistic quantum optics: The relativistic invariance of the light-matter interaction models by Eduardo Martin-Martinez el al (2018). Here he calculate the transition probability of a vacuum excitation for a detector. Suppose there is a lab where the...
11. The relationship b/w infrared, temperature, and electron excitation

Homework Statement:: 1. Does the increase in kinetic energy in (for example) water that results from increasing its temperature result from electron excitation (i.e. increasing electron energy levels) or simply increasing their velocity or vibration amplitude/frequency? 2. If excitation is...
12. I Time independent perturbation theory in atom excitation

Hello! In Griffiths chapter on Time independent perturbation theory, he has a problem (9.20) in which he asks us to calculate the first order contribution to the electron Hamiltonian in an atom if one takes into account the magnetic dipole/electric quadrupole excitations, beside the electric...
13. What is the governing equation of a spring with sinusoidal excitation?

Hi, Most of the spring vibration lectures assume spring to be fixed on one end and mass on the other end [Example]. In my case, spring has a sinusoidal excitation on one end and mass on other end. Pl. refer the image below. How to get the governing equation? With that I also want to find the...
14. Chemical structure vs excitation frequency (photons)

Is there a text, or set of texts, on how to predict what frequency of photon is released when a particular molecule is brought to an excited state and then relaxes? So for example if you were to put, say, benzene into an electrical tube and excite it what frequency would be released and more...
15. The problem of excitation of vibrations during collisions

Homework Statement Dear colleagues, my problem is following: The ball of mass with the initial velocity collides with a system of two identical balls of mass each, connected by a massless hookean spring with stiffness and length . It is necessary to find the final velocities of the...
16. Ansoft Maxwell Problem in Assigning Excitation of Current

As the picture showed, when I assigned a current excitation on the coil plane( pink one in image), Ansoft Maxwell alert ”current1 can not assigned on the entity of type face". This is incredible as I take the process completely based on the book!
17. Re: The electrical excitation of quantum dots

We most often witness the presentation of quantum dots in viles or containers which are excited via UV light. I am more interested in their electrical excitation. Could I simply take a sample of QDs from one of those viles and passing an electrical current through that sample excite the...
18. Cylindrical rotor generator power under loss of excitation

Hello all, I want to know about turbo alternator real power producing capability under loss of excitation condition. Normally in salient pole rotor have capability to supply real power under field current=0 condition, as there is reluctance power developed. But what about non salient pole...
19. A Two-Photon Excitation: Theory and Applications

Maria Goeppert-Mayer described the theoretical foundation for 2-photon excitation and it was later proven correct with the advent of lasers. Today, two-photon microscopy uses this quantum physics principle. For example, if you want to excite a fluorophore that has an excitation peak at 495...
20. B

B Understanding Excitation Energy in Atoms: Threshold Values and Potential States

My physics textbook says roughly that: Within an atom; when electrons are raised from the ground state to the energy levels that comprise their various atomic spectra, the potential energy carried by either a photon or an electron (or other) must exactly match these quantitative energy levels...
21. I Atomic orbitals: change during excitation?

Sorry if this question has been asked before or is common knowledge. It seems to me that when one or more electrons in an atom is excited to a higher energy state, then the effective potential experienced by other electrons should be different from the potential in the ground state. Hence the...
22. I Rotational excitation of quantum particle

I was watching a lecture and there was a connection drawn between classical rotational energy and quantum rotational excitation. The energy of a rotating system is $$E = (L^2) / 2 I$$ with L being the angular momentum and I the moment of Inertia. Then to make it quantum$$n^2 * ħ^2$$ was...
23. Near-resonant excitation of a two-level system

Homework Statement Hello, I have the following task: [/B] Homework Equations In the task[/B] The Attempt at a Solution I looked at this task with the notes from the class, but I can't really see through. It seems that the first step is the transformation into the single decoupled...
24. Base excitation of undamped Spring-mass system

Homework Statement I am a little stuck/unsure in an homework question for my signals and systems course. See question sheet attached. I have been able to do question 1 for the first section using FBD, and I have solved the DE using Laplace Transforms (See below for my solution). I am both...
25. Temperature Calculation for a Distant Star with Thermal Excitation

Homework Statement The spectrum of a distant star shows that one in 3x106 of the atoms of a particular element in its first excited state 7.3 eV above the ground state. What is the temperature of the star? (You can ignore the other excited states and assume the ratio of statistical weights is...
26. B Photoelectric effect and atomic excitation

A few quick questions I'd like cleared up:1) Alkali metals are said to have a really low threshold energy, enough for visible light to cause the photoelectric effect. Does this mean if I aim a flashlight (turned on) at a piece of sodium, I could ionise it? Simply flashing a light over a piece of...
27. Why Fluorescence is detected @right angle to the excitation?

Hi everybody, I would like to know what would be the best angle (or best geometry) to put the detector relative to the light source in order to observe the emission radiation from the fluorescent materials? As I know the most common geometry used for fluorescence is right angle observation...
28. Engineering Diode circuit with AC excitation source

Homework Statement Graph ##V_{out}## Homework EquationsThe Attempt at a Solution When ##V_{in}=V## C1 is positive on the left and negative on the right, and C2 is negative on the the down side and positive on the upper side so there is no Vout?
29. A Incandescence and electronic excitation

As far as I experienced, incandescence happens in a wide variety of materials no matter what a substance (conductor, insulator and so on) is. Does this effect is related to the electronic excitation? Could anyone please explain the reason of this effect?
30. I Photoluminescence Excitation (PLE) vs PL spectroscopy

I'm not sure I understand what information we can get from Photoluminescence Excitation (PLE) that we don't get from regular PL. Let's imagine we have a sample with emissions between 700nm and 850nm. If I'm not mistaken in a typical PL experiment you'd just use a laser source with a wavelength...
31. Problems in excitation and boundary while doing ANSYS transient

hi, I m designing a current transformer in ansys. initially i designed a 3D toroidal (split) core. i wanted to get the B-H curves by varying different permabilities of core with different frequencies.the current injection is through the conductor which is in centre of core. but i am facing a...
32. Excitation of a hydrogen atom by electron collisions

The problem: A beam of electrons with kinetic energy 12.8 eV collides with a hydrogen target. What visible spectral lines will be emitted due to collisions? My question: I am confident I know how to do the bulk of this question, I am just uncertain about one thing: I know that 12.8 eV is enough...
33. Can Sodium Ions in the Brain Be Excited with Electromagnetic Radiation?

Is it possible to excite the sodium ion in the brain with photon from electromagnetic radiation to create a yellow glow like the sodium-vapor lamp here? Please bear with me, I'm bad with Chemistry
34. What are the conditions to excite an atom by collision?

I know that an atom can become excited in one of two ways: by absorbing some energy from a source of electromagnetic radiation or by colliding with some other particle—another atom, for example, but my question is about the second part. So I want to know how and in what conditions (pressure...
35. Energy Excitation: Why Electron Emits Radiation

Why doesn't an electron which has been excited not keep the energy gained and stay in a higher quantum level? Why does it prefer to emit radiation and return to a lower energy level?
36. Excitation from unbalanced mass

Homework Statement A rigid body of mass M slides vertically inside a friction-less prismatic pair. It is linked to the fixed frame through the spring of stiffness k, and a viscous damper with coefficient c. Beside the body, a point mass m rotates with constant speed w(omega) on a circular...
37. Nuclear Nuclear Theory: Excitation Mechanisms of the Nucleus v. 2

I am looking to purchase the third edition of this title by Judah Eisenberg and Walter Greiner, so far I searched through amazon and bookdepository and abebooks, but I didn't succeed in finding any copy of this edition for sale. Anyone knows where may I find a copy to purchase?
38. Digital logic excitation equation from state diagram?

Homework Statement Design serial transmitter circuit take 8-bit word in parallel as input, when an input control signal (SEND) goes high, and serially outputs the word (i.e., one bit during each clock cycle) to a single transmission line. Transmission of a word begins with the least...
39. Photon excitation to full orbitals

In introductory physics and chemistry, photon excitation is usually illstrated with a simple hydrogen molecule. I am wondering what happens if an electron is excited to an orbital that is already full. Would the orbital split up into different energy levels as hybridisation, so as not to violate...
40. QFT, excitation of quantum field, physical or mathematical?

In, QFT, an elementary particles is an excitation of its quantum field. Quantum fields are just mathematical. For example an electron is excitation of the electron field. But is the excitation of the field physically real or just mathematical? What i mean is, is there something physically...
41. Is an electron a delocalized excitation before measurement?

When we observe an electron it is always a localized excitation in the electron field. But when it's not being observed, does the excitation begin to spread through space and become a delocalized excitation?
42. I On liquid oscillation excitation

(I'm new to the Forum, so if I violate the rules unknowingly, please do let me know) So, during a recent research, I analyzed the frequency spectrum of our hand's oscillation while walking. As it turns out, it contains distinct harmonic frequencies (around 1.8*n Hz), and the second among them...
43. Synchronous generator excitation

I recently read about synchronous generator and some things really confuse me.. How does the excitation affect reactive power? I don't understand their relation.. For constant load and variable excitation, how does the power factor change? Icosø remains the same but both I and cosø change with...
44. Collisional excitation: selection rules for rotations?

To be specific, I am referring to CO molecules undergoing collisions with H2, resulting in CO transitioning to an excited vibrational state. I can't seem to find any rotational selection rules for collisions, meaning ΔJ could be essentially anything, as long as energy and angular/linear momentum...
45. Field Excitations and their Collisions

How do collisions occur between different particles when the field excitements that make them are not the same? Also how do you collide when the field are the same? Wouldn't the values of the field just increase until the particles pass through each other? (Like a constructive wave). What I mean...
46. Ansoft Maxwell - Multi terminal excitation on 3D Transient

Hello everybody,I am busy with a magnetic transient 3D model and quite new in the use of Maxwell. I am simulating a 6 pulse rectifier in double star connection (connection number 5 as per IEC 146-1-1). Each of the 6 arms of rectifier foresee 8 paralleled diodes. I am interested to see the...
47. Excitation of two-atom state by single photon : FTL hope?

This concept is rather interesting : "Excitation of two atoms by a propagating single photon pulse" -- http://arxiv.org/abs/1411.3445 . They say that, in principle, one can tailor an optical pulse so that it will excite two atoms from the ground state (i.e., the |gg> state) so it ends up in any...
48. Base excited stacked mass spring damper systems

Homework Statement I'm trying to derive the equations of motion and state space as well as the transfer function for a system which has two mass spring damper systems stacked on top of each other. The system is base excited. I attached a pic of the system Homework Equations - Sum of the...
49. Excitation of electrons by electromagnetic source

If you hit a bound electron with a photon corresponding to that electron's ionization energy, you ionize the electron. What if you hit the electron with a photon with less energy? Will the photon still add its energy to the electron? Will the electron re-emit the photon with less energy? Do you...
50. Understanding Flip-Flop Truth & Excitation Tables

I am not getting these truth table & excitation table for a flip-flop.. I mean I can understand it but what is the difference between the two?? they are same to a large extent what actually is differentiating an excitation table from a truth table??