Feedback Definition and 239 Threads

Hello! I am locking a ~30 kHz linewidth laser to a ~100 kHz linewidth ultrastable (ULE) cavity, aiming to reduce the laser linewidth to ~ 1 kHz using PHD locking. The feedback signal is sent to the laser current (it is an external cavity diode laser). For PDH the modulation of the EOM used to...

Dear Physics Forums members, I want to address a serious mistake that has impacted our community’s trust. A deeply regretful error of judgment that I alone am responsible and accountable for. No other staff had any knowledge. During the past several months, to counter declining engagement, I...

How did you find PF?: Google search Hi everyone, I’m applying for the Erasmus Mundus Scholarship for the Quantum Science and Technology program, and I’ve already written my motivation letter. I would greatly appreciate it if you could review it and provide feedback to help me improve its...

Congratulations Amazon! You made yourself unquotable! I was looking for a link to Spivak's calculus book and Amazon told me that they only show me results that can be shipped to Germany although I was on their American page! What? How in the world should I know where people who read my link...

The answer should be around 39g. I keep getting around 45g. This is the calculation I tried Any feedback on what I am doing wrong ? Regards!

Well I got my second strike in some weeks, and this is one I do not agree with. I had cut part of the comment to paste it in twitter, there was an extra line linking to the 2004 thread and a final one commenting on Lubos et al conjecture, but well, this is the surviving thing. I do not see a...

https://www.physicsforums.com/posts/7123135 And several earlier posts show differing "In xx minutes". Have fun!

Hi, I wonder if someone can help with the following problem? We have a sealed box in space and inside the box is an electric motor with the stator attached to the box. The rotor arm is attached to the inner race of a bearing and the outer race of the bearing is also attached to the box. There...

I spent the whole day trying to figure why transresistance amplifier modelled with z-parameters does not match with nodal analysis results but I sill can't figure out. I desperate need help on this... I write down step by step what I did for a very simple transresistance amplifier here and hope...

Hello everybody I have being in PF for about one month and a half and I would like to share my advice on my experience on the site so far. I am still figuring out how it works and what is the best use of this site. Due to some setbacks I have mixed feelings but still positive on continuing...

Sorry, but what on Earth are trophy points for? I can see that they get awarded for meritorious behaviour - like joining PF in the first place - but when you've got them, what can you do with them? Or are they like any other trophy that you put on a shelf to gather dust? I just got one for...

The mentor list in https://www.physicsforums.com/help/mentorforums/ is not complete. Shouldn’t there also be a list of various advisors near here?

Hi, Curious if there is an expression for a negative feedback system that experiences phase shift. For example, at 0 degree phase shift, the additional gain is 0 because it is fully negative feedback. At 180 phase shift the additional gain is infinite because you have full positive feedback. Is...

Solutions are also attached as a file

I like creating physics and chemistry problems and i want some feedback on them. What is the most appropriate forum to post them and ask for oppinions?

Good afternoon! I am fumbling my way through setting up a JC model in python, I was hoping I could get some feedback on it please. I just want to make sure everything looks good and the data I am collecting is valid. Any advice or feedback would be very welcome...

I have used root locus before but my confusion now is that the input is the negative feedback. Usually when I have negative feedback I consider the the error between the input (ideal) signal and the observed signal. Also, in this case what is the tranfer function since u = -k*y, and what does...

I was puzzled when I thought about what happens to a klystron when it's output is fed back to it's input. This doesn't apply to magnetrons because they cannot be driven like amplifiers so they are oscillators by definition. I've dealt with audio amplifiers mostly and there almost always...

Hi all, I'm trying to derive fuel temperature coefficient in a TRIGA reactor using a monte carlo code. When i do that, if i assume a radial temperature profile along the core, i obtain smaller value (-7pcm/K) than the one achieved with uniform temperature (-9pcm/K). More in detail: in my case...

In this case, there is negative feedback. ##V_{out}## is almost equal to ##V_{in}## in this case. But I really can't understand how to even proceed to find out the input impedance in this case, from the equation I know. Can someone help me out in figuring how should I proceed?

I am still trying to find somewhere to post to report this problem. If try to visit and post in Feedback, or if I try just to VISIT the "Advertisements" topic there, the only page that loads is this: "Page could not be loaded,... " and I cannot even post the whole page message here because...

\newcommand\func{\(f\)} \newcommand\myset[1][math]{\ifthenelse{\equal{math}{#1}}{\(K\)}{K}} \newcommand\diff[4]{\(|#1-#2|#4#3\)} \newcommand\ball[3]{\diff{#1}{#2}{#3}{<}} \newcommand\Fllab[2]{\diff{f(#1)}{f(#2)}{\epsilon}{\geq}} \newcommand\term[2][n_k]{\({#2}_{#1}\)}...

This is the circuit in question. During lecture, when checking whether this was negative feedback, my instructor said that if the v_out increases, then v- increases as well, which would lead to the next v_out decreasing because v_out = A(v+ - v-). I get how if v- increases the next v_out would...

I had a bunch of questions regarding the feedback component as well as the feedback mechanism itself. 1. I am using the attached schematic as reference for my design. As per the LM2576 module data sheet, it can handle a maximum current of 3 A whereas I need the IC to handle at least 15 A...

I recently started looking into a boost converter design that would be no load most of the time which causes it to operate in DCM. After calculating the duty cycle D, it is dependent on Vi, Vo, L, f, and R. The load R and output voltage Vo are fixed, but I would like to vary the other parameters...

Hi! I'm a high school physics student. I really, really love physics, especially rocket science, and I had an idea about a rocket design, but I don't know how feasible it is. I was hoping you guys could give me some feedback. So I was learning about electricity, and as far as I know, electric...

The book says that " The op-amp multiplies the potential difference between V+ and V- by the open-loop voltage gain to produce Vout." So my first question is, since we say we assume open-loop voltage gain is infinite, so does that mean the Vout produce will be infinite too? Then, the book says...

I built the tool initially for myself to better understand how Lorentz Transforms and spacetime diagrams work. Then while trying to discuss it with a friend I need to put it online and it snowballed from there. Now I am wondering whether there is any value for others in what I have created...

I know that when the feedback is connected, the voltage gain changes by the above formula. But I don't know how to find final values of input and output impedances.

In an op-amp with negative feedback, say initially the + input has some small positive value and the - input is at 0. Then the op-amp amplifies this difference, and a part of it is fed to the - terminal through resistances. This will increase - and will lessen the difference. My question is...

I have a laser and I am adjusting it's position using a motor, and I am reading the laser light intensity at the top and bottom using a sensor. then I divide the top from the bottom and the goal is to get around 0.97%. This is called delta, if delta is too high, you move the motor lower and if...

I'm not sure how will this oscillator work. Assume A is low, so B will be high and the capacitor will charge through B-C- 2Mohm. Now even D has gone high, so A will be high and B will be low and C will discharge. I'm not sure how the voltage divider rule across RC will take into effect. I found...

This is my motivation letter for the university of Regensburg (Masters). The bad thing is that my grades are above average, not great. And I have little to no research experience due to my BSc school. I avoided useless mumbo-jumbo and flatter so it's going to be short and to the point. I pushed...

Just need a bit of guidance to make sure that I am heading the right way. Question is: Fig 3 shows the block diagram of the control of an electric heating system. The heater is driven from a voltage-controlled power supply, the voltage V1 being derived from a potientiometer. The output...

From this table: Looking at the 7 row and taking the first entry, 1 This is 000001 Adding back the highest and lowest bit: 10000011 And then the equation would just be x^7 + x +1 ? Or taking the taking the third entry, 7 This is 000111 Adding back the highest and lowest bit: 10001111 And...

We express such equations by $$\frac{dx}{dt} = \beta - \gamma \cdot x$$, t denotes the time. In this case, γ depends on x, thus the dynamic equation should probably be: $$\frac{dx}{dt} = \beta - \gamma(x) \cdot x$$ 1. Setting the equation to 0 leads to two different cases: If x < K: xST = γlow...

From my understanding, the root locus is only concerned with open loop gain. I figured this means you would ignore the negative feedback loop and calculate the root locus from just the plant's function Workings: zeros: -1 poles: 0, -2, -2, relative degree = 2 => 90-degree asymptotes meeting...

Homework Statement FIGURE 3 shows the block biagram of the control of an electric heating system. The heater is driven from a voltage-controlled power supple, the voltage V1 being derived from a potentiometer. The output temperature, θo is subject to distrubances, θd, because of changes in...

I took a stab at simplifying Special Relativity, but I want to be 100% sure I'm not butchering physics in the process. Anybody care to weigh in on that? Here is a draft of my Medium article: https://medium.com/@philipkd/special-relativity-explained-with-a-deck-of-cards-f99bfd873bd5 Thanks, - Phil

I want to create a small pad consisting of two electromagnets that repel and attract each other, this can give the feeling that something is pushing up against your skin if held. Is this a practical idea?

Homework Statement Hi, Here is what I know about the Ideal Op-Amp. - The open loop voltage gain is infinite - The output voltage is given by the following $$v_o = A(v_+ - v_-)$$ - Only with a negative feedback loop is $$ v_+ = v_-$$ My query is with regards to the negative feedback loop...

Homework Statement Choose a technology such as MP3 players, laser, medical imaging, or another that interests you (Other than the cell phone). Research the internet and find out how it is related to the physics of light and waves. In approximately 100-150 words, write a paragraph explaining the...

Hello! I don't really know how High School ends in other countries but in Sweden it ends with an examination project depending on the programme you've selected. Anyhow we were free to choose one research topic that is related to mathematics, physics, biology and chemistry. I choose the brain...

Homework Statement [/B] Homework Equations Adiff(single-ended)= 1/2gm*ro||Rd β=R2/(R1+R2) The Attempt at a Solution I am really confused as to how to find A. I know the feedback of the circuits around the R2 and R1, but I don't understand how the open loop gain can be found. Can someone...

In this example: The input multiplier to the artificial neural network, at the bottom of the screen, for each note is determined by an output of an Expectation Maxamazation sequence that converges after ten iterations with input of the artificial neural network's output above a threshhold...

In a positive feedback amplifier, as I understand, output of the amplifier is fed back into the input of amplifier, essentially creating a loop. My question is specifically, how the loop does not go in an infinite cycles ? what prevents it from going into an infinite loop ? How many cycles...

Hey, I just thought I would share some of my video art. They are meant to be visuals going alongside Techno / House music in the nightclubs of Berlin. However I got a lot of ideas from reading up on physics, like diffraction patterns, fractals, polarization of light / materials, lenses, video...

If we consider an efficient measurement performed on a system in a pure state. How would we use feedback (by applying to the system a unitary operator that depends upon the measurement result), to prepare the system in the same final state for every outcome of the measurement (this can be done...