Short Definition and 523 Threads

Dear All: I like to write and I’m a physicist myself. Right now, I’m currently outlining a short sci-fi story called “Borrowed Time”. It goes as follows: In the near future, science has conquered the technology that allows the manipulation of the flow of time. Space and time limitations, as...

Hello! I want to induce a (weak) signal in a wire across the room from me. I was just wondering, how would I go about doing this if I couldn't touch the wire and couldn't modify the equipment to accept these signals BUT was close and in line of site of the wire?

Hi,let: 0->A-> B -> 0 ; A,B Z-modules, be a short exact sequence. It follows A is isomorphic with B. . We have that tensor product is right-exact , so that, for a ring R: 0-> A(x)R-> B(x)R ->0 is also exact. STILL: are A(x)R , B(x)R isomorphic? I suspect no, if R has torsion. Anyone...

Hi everyone, I am working with a solar cell realized with a metal-semiconductor junction. I need to find an expression for the short circuit current of this solar cell, but in the literature I have only found models for the standard case of a pn junction solar cell. Does anyone know a...

I'm building a telescope and one of the more important choices I'm making is what focal length to make the mirror, my understanding is the longer the focal length the closer you see far away stuff, but the field of view diminishes a bunch. I've seen both long tube dobsonians and short tube ones...

So I'm designing a system that requires an extremely high amount of current for an extremely short pulse lengths. These pulses would be consecutively spaced at relatively large intervals from one another. I'm just wondering if there is some sort of instantaneous power limit to wires, even if the...

I want clarity on STC rating that is 25kA or 16kA or 18.4 kA. If I want to change my Specification of 12kV Indoor Breaker from 16kA to 25kA STC rating then how can I support my self. What are advantageous points. Please clarify me.

I have attached one circuit. I don't know why we consider the rightmost capacitor gets short circuited. And what do you mean by short circuit ?

My doubt is about the circuit in the picture. The capacitor is charged ans the switch open. There's a voltimeter connected to the terminals of the capacitor. Does a current flow through the wires of the voltimeter causing a short circuit? If not, what would happen in the circuit described...

Homework Statement a)What value does ##\left(\frac{\partial U}{\partial V}\right)_T## tend to as T tends to 0? b)A heat pump delivers 2.9kW of heat to a building maintained at 17oC extracting heat from the sea at 7oC. What is the minimum power consumption of the pump? c)Explain how a...

I am trying to write down a compact form of S = A+L/(B+C)+L/(B-C), does it make sense in general to write down S = A+L/(B\pmC)? Update: I have simplified it too much in the minimal working example, the denominators is actually more complicated, let me elaborate...

Homework Statement 1) If one is using light bulbs to detect phase sequence then it is wise to connect them in series with circuit resistor. Why ? 2) There is short circuit in phase "A". In which case is short circuit voltage larger, in four-drive (?) system or in three-drive (?) system ...

Hello guys, I have to make a short circuit calculation for school but I am a bit lost.. I have a copy off the IEC61363 and internet connection as my help lines. Homework Statement The network consists of a generator feeding to switchboard A with a cable in between, on the same...

The question is fairly simple but I am afraid the answer will not. I have seen many information about magnetic force between infinite parallel wires but almost nothing about finite ones. So, let's have two finite parallel wires, each one 50cm length, in 10cm distance, both have the same...

That 2 terminals shows PD of 1 volt on Meter, but when shorted, there is no current shown on Meter? I checked and rechecked [using different meters, wires, AC, DC options and what not], so I see only V measurement, but no I. Is it possible? If so, then what is the use of that PD, when we can't...

Hi All, I am trying to make a system which supplies a large burst mode AC signal to a piezo and then short circuits the terminals once the burst is over( here in the literature). The system has a Function Generator attached to a High Power amplifier which is attached to the leads of the...

Homework Statement Homework Equations The Attempt at a Solution I am trying to find the value for i as i→∞. Since ∞>0, I must look at the circuit when t>0. However, when t>0, there is a short circuit. I know that you can short circuit resistors so I can easily short circuit the...

Consider two points A and B (Fig.1) at rest in S frame having a distance L0 between them (a long scale may be imagined as placed between A and B). ------ (1) The ‘traveler’ twin (S-frame) starts from A at time t = 0 and suddenly accelerates to attain a constant velocity v in the view...

Here find some attached circuit of three phase cabinet which operation voltage is 400V /415V and have operated current 800A, fault current for 1 sec is 46 KA and have incoming and outgoing links with one phase Lighting and socket. I want to know is there some method that one can calculate...

Homework Statement A 50 KVA,6360 V/230 V transformer is tested on open and short-circuit to obtain its efficiency,the results being as follows: O.C.: Primary Voltage-6360 V, Primary Current-1 A, Power Input - 2 kW S.C: Voltage across primary winding-180 V Current in secondary...

Homework Statement http://postimg.org/image/b8p4rszot/ There is a short circuit between the terminals a-b Homework Equations The Attempt at a Solution so I found the node voltages at 1 and 2, but I don't know how to use these to get the short circuit current...

Homework Statement For a spin 1/2 system, the eigenstates of z-component of the angular-momentum operator Sz are given by: S_z |\pm> = \pm \frac{\hbar}{2}|\pm> Suppose at time t, the state of the system is given by: |\psi> = a|+> + b|-> If Sz is measured, what are the possible results of...

Hi everyone, this my first post in here. Anyway, this is a solved problem, but I can't get the answer :S Homework Statement Homework Equations * Series-Parallel combination (RT=R1+R2+R3...+Rn for series, 1/RT=1/R1+1/R2+1/R3...+1/Rn for parallel) * WYE (TEE) - DELTA (PI)...

A satellite orbiting the globe at some 300 miles at 18000 mph. Does the clock on the GPS tick slower or faster than the same clock on Earth? 1) the clock is distant to Earth and is under less gravitational pull, resulting in time slowing down less than the Earth clock, therefore ticks faster -...

I know this isn't a counselling website, but what the hell, here goes.. A little bit of background: Hi everyone, I am a Physics student at a UK university currently in my 3rd year of a 4 year MSci (Integrated Masters) degree. I am doing well so far on my course, I achieved an average of...

0\rightarrow A\rightarrow B\rightarrow C\rightarrow 0 is a short exact sequence if the image of any morphism is the kernel of the next morphism. Thus, the fact that we have the 0 elements at the two ends is said to imply the following: 1. The morphism between A and B is a monomorphism...

I had 4 1.2 volt guys lying around in a holder. The 2 wires sticking out were lying around and I started smelling stuff. I look down and I see they are connected together and the steel points seem to be slightly melting together, the batteries were hot, did it damage them or is this okay?

Hi, After adding a wire across a circuit to section off part of the load in the form of a short circuit, I am still seeing a couple of milliamps flowing through the load. Is this due to the fact that the wires used to create the short circuit will have a small amount of resistance, hence...

Is it correct to define matter as a force moving primarily in time dimension, and energy as the same force moving primarily in space dimension of spacetime?

Prove that if (a_n) is a null sequence and (b_n) is a bounded sequence then the sequence (a_nb_n) is null: from definitions if b_n is bounded then ## \exists H \in \mathbb{R} ## s.t. ## |b_n| \leq H ## if a_n is a null sequence it converges to 0 (from my book), i.e. given ## \epsilon ' > 0 ##...

Hello I asked a question about infrared and UV a while back for which I got some very informative responses: https://www.physicsforums.com/showthread.php?t=676881 This is in a sense a very short follow up question: Is the reason that we don't feel 'heat' from an infrared remote...

My book has some questions involving "short links" connecting trusses to a support. It doesn't seem to explain what short links do. Can anyone shed some light? I attached a picture of what they look like. I really just can't find any information on what they do. Is it supposed to be very obvious?

Question http://gyazo.com/17223631de9dfcbcca00f6b3f8758cb9 I'm talking about part ii) if ## a = |\vec{BC}| ## then ## a^2 = (\vec{OC} - \vec{OB})^2 ## is this correct? if we expand a^2 then we get ## a^2 = (\vec{OC})^2 - 2\vec{OC}\vec{OB} + (\vec{OB})^2 ## I don't understand, what is...

I am having trouble understanding short circuits and would appreciate some help with it. From what I understand, a short circuit occurs when we have a connection with a very low (zero) resistance is made between two points in a circuit. With R=0, the only resistance in our circuit would be...

Hi, I hope this is the right forum to ask the following: January has 31 days, February 28 and March 31 : 90 days in total, is there an astronomical reason why we do not have three 30-day months?

Hi! I'm having problems understanding the last step of a derivation for a version of a theorem of Gromov's we had in class: In short, the proof takes the Riemannian universal covering (\tilde M, \tilde g, \tilde p) of (M, p) and uses a short basis (\gamma_1, \gamma_2, ...) of the deck...

In Dummit and Foote Section 10.5 Exact Sequences (see attachment) we read the following on page 379: "Note that any exact sequence can be written as a succession of short exact sequences since to say X \longrightarrow Y \longrightarrow Z [where the homomorphisms involved are as...

Hi everybody. I would like to find out the exact script of a short video that I intend to show to my French pupils who learn physics in English at school. If anyone could give me a hand, it would be nice. This is the video http://vfsilesieux.free.fr/curiosity/video.swf (you may have to...

Hi, Would someone care to please explain why no current passes through R1 (see attachment) in case Vs is replaced with a short and the inductor is considered a short too (in the steady state, for DC)? Why would the R1 branch be open and not short? Is it not in parallel with short under the...

Homework Statement What do a capacitor and a selenoid have in common? Homework Equations The Attempt at a Solution

Am i right? Short things can be faster! theyre moves, to do things are short . and they can finish they jobs more fast for example falling of 2 meter and 5 meter tree . Both fall on same time but 5 meter tree must and in did fall by higher speed than 2 meter tree Or Openning a big door or small...

A short word for "acceleration" (pedagogy) I tutor physics, and I am good at explaining to students what acceleration is. I teach them to disambiguate kinds of motion--because before studying physics, most people get by without separating velocity and acceleration as concepts. I know how...

Infinities in QFT come from high momenta. I sometimes hear that is equivalent to coming from short distances, but I'm not sure I see the connection. The free propagator G(x-y) which I think goes like 1/|x-y|^2 is singular for short distances (when x=y). In momentum space G(x)= ∫d^4k exp[ikx]...

I'm currently a 2nd year undergrad student. I have done introductory courses on Mechanics and Electromagnetism, with the corresponding maths required for them. I am trying to figure out where my interests lie in order to apply for Grad school next year (my degree is of 3 years). I need a list...

Why voltage in a short circuit is 0? I=U/R , R goes to 0, I goes to infinity => U=IR= 0 times infinity, i don't get it, why 0 "wins" here? Thank you!

Homework Statement Problem number 6a in the picture. Homework Equations Transistor: Ic = βIb Ic = αIe Ic = Is*e^(Vbe/nVt) OP-Amp: Vo = Acl*Vi Acl = 1 + (Rf/Ri) The Attempt at a Solution I tried to solve but just couldn't understand the behavior the transistor.

The "Rule of Four" in calculus is the teaching philosophy that all concepts should be taught algebraically, graphically, numerically, and verbally. In particular, when dealing with functions, the teacher should emphasize the algebraic, graphical, numerical, and verbal representations. I could be...

In Deep Down Things, an excellent book of B Schumm, at page 288, he explains that the weak force is short range because the Weak quanta have a large mass. Using de Broglie wavelength relation: Lamda = h / p, he gets a wavelength of 10 ** -18 m, and he concludes that this is the W quanta range...

Homework Statement If both k of the spring and m are doubled while the damping constant b and driving force magnitude F0 are kept unchanged, what happens to the curve, which shows average power P(ω)? Does the curve: a) The curve becomes narrower (smaller ω) at the same frequency; b) The curve...

I am solving a VERY complicated exercise and I have this part that I don't understand.The image posted is a very big simplification of a part of the exercise.I have to find the potential between A and B.My question : Are the 15 Volt and the 13 Volt in the picture involved in the calculation? I...