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The physical length of the transmission line in relation to the wavelength of the signal being propagated determines if the line is electrically long or short. It varies depending on the source, but typically, an electrically long line is at least 1/4 the length of the signal wavelength.


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What you understand has to be refined a bit. Potential is defined referring to what happens to a positive charge in a field. A positive charge is moved by the electric field from the higher to the lower potential. Therefore, a negative charge is moved in the opposite direction. See the diagram: Now to your formula: Indeed, for a positive charge in an ...


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Take a battery of 4,5 V. Take one light bulb and some wires and arrange a simple circuit, measure the current, and lets say it is 2 A. Then, take another light bulb and connect it in parallel to the first one. Overall current will now be 4 A, it will increase. The rule is intact, as you can see, because in each branch now you have 2A which ads up to total of ...


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Think about the power supplied to the bulb. Assume for a moment constant voltage source, and constant resistance for each bulb (not true for bulb but often used to simplify discussion at this level) then in series you have a total resistance of $2R$ and power $P= VI = \frac{V^2}{2R}$ . This power is split by two bulbs so each sees $V^2/4R$. When the bulbs ...


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The bulbs will only appear brighter if the available current to the system is not limited. In that case the series bulbs will have a lower voltage across each individual bulb and they will appear dimmer. If the power input to the circuit is a constant than the total wattage output from all bulbs is also constant and the bulbs will all appear the same ...


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Although dry wood is a relative "good" insulator, a tree is not a good insulator because of the sap/water inside it. Most likely you touched the tree at about the same height as the fence. If the tree has about a 10" diameter, you might have the equivalent of 2" of insulation (and 8" of water), that means most of the voltage will be dropped across you ...


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There is no such perfect insulator. Depending on conductivity materials are loosely classified as conductors, semiconductors and insulators. As Potential difference between two points in the medium increases the material begin to conduct at some point. The nature of the material also crucial here. If it contain ions then charges easily flows. Hence the ...


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because electrons can be easly removed where as protons are bonded to neutron so it will become an atomic bomb if you want to remove protons.


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Suppose we have a pump submerged in a liquid of density $\rho$ at a depth $d$ which we want to use to raise the liquid to a height $h$. The pump has to do work to overcome the potential energy difference between the two heights of liquid. That is: $$W(t)=\rho Qg (h-d)t$$ Where $g$ is the acceleration due to gravity (taken as $9.81m/s^2$). $Q$ is the ...


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I have the same problem with my bathroom fan knocking out my tv, electric motors in general produce an electic field that interupts your signal pattern, also yes i am amazed you have a signal at all with the cables like that, its fairly easy to join them strip both ends back join the 2 inner cores in a connector then twist the stranded outer cores together ...


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Trees are not as good an insulator as you might think. This source suggests a typical conductivity of living tree sap is 0.01 S/m with a relative permittivity of 80. So not an insulator, though a poor conductor. Typical advice when using electric fencing is that you do not use wooden posts! Presumably because wet wood is also conductive to some extent. In ...


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"Wood is an insulator" is a very broad statement. In fact it's wrong. "Wood is not a good conductor" would be a more accurate statement, but moisture in a living tree would easily carry enough current to give you a shock and have enough resistance not to trip out the breaker/discharge the battery powering the fence.


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It won't kill you if you touched the side after the transformer, that is the side that connects your laptop. The transformer is the big black box. However if you touched the side that is connected to the the Power Socket and were properly earthed you would have died assuming the current flowing from the the power board was not limited by placing some kind ...


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It depends which side of the transformer the cable is broken. The cable from the mains outlet to the transformer carries 250V AC. If you are NOT well earthered, for example, you are on nylon carpet, or wearing rubber-soled shoes, then the electricity will not travel through you very well, and will get a severe shock. But if are well earthed, ie., there is a ...


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It would be the current that would cause damage and assuming your laptop had a 3 amp fuse in the plug top then yes across you chest 10 - 20 milli amp can stop your heart. Electrical engieer


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Yes there is an electric field outside of a current carrying wire, in a direction along the wire axis (i.e. parallel to the wire). This is true in both the AC and DC case. There is also of course a magnetic field in the azimuthal direction. For a resistive wire oriented along the z-axis, the electric field inside the wire is given by Ohm's Law $E_y=\eta ...


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The torque on electricity generators is continuously adjusted to keep them running at a constant speed (e.g. 60Hz in the US and 50Hz in the UK). When you turn on some electrical item the current it consumes places a greater load on some electricity generator somewhere and this reduces the speed. To counter this, at the generating station more torque is ...


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Power generation and supply management is not easy and it is to their credit that most of the time power companies supply people with AC at the same voltage no matter what the demand for power is. So when we turn on appliances we do not see the voltage drop as a result. Or more realistically when everyone gets home from work and starts cooking/ boiling ...


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The live found a route to earth, discharging it's energy on whatever load was connected between live and earth, and then luckily the RCD cut off the supply before you cooked yourself.


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That is called EMC : Electromagnetic compatibility. Your DC machine stator is fed through a brush. Since it is rubbing the commutator plates, it can generate sparks, small arcs and so on. Since these phenomena are really fast, they tend to emit electromagnetic radiations in the whole frequency spectrum (see the Fourier transform of a dirac delta function) ...


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The answers posted by CIA and dmckee are great, and they correctly point out that textbooks usually handwave about why electrons don't easily leave the surface of conductors, but I would add that the electrons actually can move through the air, even if the electric field is not strong enough to ionize the air and form a plasma. Anyone who has tried doing ...


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The first equation is the definition of the polarisation field. The second equation is not a definition and is only true in limited circumstances - those dielectric materials where the polarisation is indeed linearly dependent and in the same direction as the applied electric field. The connection between the two in those materials where this is true, is ...


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You seem to be asking about mode transformers; these are extensively used in antennas as they connect to waveguide feeds. The waveguides usually employ TE10 (rectangular) or TE11 (circular) modes, but if you want to feed a horn, say, then you have to shape the field properly to avoid reflection, reduce sidelobes, and reduce cross-polarization coupling, etc. ...


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You want to learn about the Biot-Savart Law which allows you to calculate the field at any point in space caused by an arbitrary current distribution. From the above link: It basically describes the field $dB$ due to a current $I$ in a tiny wire of length $dL$; to get the value for a big wire you simply sum over all those littlewires. To really understand ...


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Gas can conduct electricity under two condition using a discharge tube; (1)low pressure (about ~0.01mmHg) (2)high voltage (>1000v)


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Gas on its own cannnot conduct electricity but it can be made to conductor electricity by subjecting it under LOW PRESSURE and HIGH VOLTAGE.


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Why are electrons attracted to a magnetic field? Perhaps nobody knows. You can know the name of a bird in all the languages of the world, but when you're finished, you'll know absolutely nothing whatever about the bird... So let's look at the bird and see what it's doing — that's what counts. I learned very early the difference between knowing the ...


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Moving charged particles are not attracted by magnet, but turned direction by them. This is what required in CRT -- to aim beam to different points. Also it is possible to build focusing devices of magnets: https://en.wikipedia.org/wiki/Magnetic_lens


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It is because of the Lorentz force, a basic law of electromagnetism. Its expression is $\vec{F}=q(\vec{E}+\vec{v} \times \vec{B})$ What this means is that an electrostatic charge is only influenced by a magnetic field if it is moving (the first term is just the electrostatic force). The other is that the force is perpendicular to both the magnetic field ...


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Looking at the expression you wrote in the comment to @nvvm's answer, you are getting your units messed up. If you just convert everything to SI units, and write the units during your evaluation, you should see where your problem is. You wrote I would rewrite as $$\begin{align}\\ \frac{dT}{dt} &= \frac{I^2R}{\ell\cdot A\cdot c_v}\\ ...


3

It's given that volumetric heat capacity = c is 3.45 joules per kelvin per cc that is equal that the heat necessary to heat up 1 cc of cooper for 1 K is c, so $\Delta Q = CV \ \Delta T$ where $V = lA$ is a volume.


2

Every time two dissimilar insulators rub together, there will be a relative buildup of charge due to the triboelectric effect. In essence the two materials stick together briefly, and when they unstick the electrons may prefer to stay with one surface and not the other. This happens summer or winter. The reason you get "shocked" more in winter has to do ...


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You do not many etails of the setuo, but I assume it an electrical dischage in air inside a closed ball, like in some museums? If such is the case, differnt elements mixed with the air will get the atoms either ionized or some electrons exited to exited to a higuer energy level. When these deay back to their original energy they emiting light of a specific ...


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The norm CEI 287 will give the method of assessment of the resistance of the conductor including the parameters you mentionned. Basically, the method that is used (to my knowledge) is the ohmic losses formula with a corrected resistance due to skin and proximity effect. About the skin effect, you can assume that the current is only flowing in an external ...


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What we call 'earth' or 'ground' in electrical / electronic circuits is a 'reference' point for electrostatic potential. There are generally several 'types' of 'earth' used in this sense. An 'instrument earth' or 'signal ground' is used as a reference for low level signals, such as those used in communications devices. So when we say 'the USB power pin has ...


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You are expected to get an electric shock if you poke your finger in the live side of an A.C. supply and have a bare foot on the ground. If you poke in your finger to one terminal of a D.C. supply and you have a bare foot on ground, you will not get an electric shock. This holds valid, unless you use very high voltage of D.C. supply in which case you will ...


1

The first equation is when you want to solve for either the voltage, current, or power already knowing the other two, similar for $P=I^2R$, when you want to solve for an unknown already having knowledge of the other two. The last equation you get by noting that, $P=IV=I^2R$, hence $V=IR$ or $I=\frac{V}{R}$ plugging this into, the first equation you get ...


2

Yes, a force is still acting on the particle. Moving perpendicular to the lines of force may result in no work being done ($W = \mathbf{F}\cdot \mathbf{r}$) , but since the particle is charged, it will be experiencing a force when moving through any electric field. If the particle is (initially) moving in the $y$ direction and the electric field is in the ...


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I already got the answer. because transformers simply doesn't work in high voltage environments. High voltage environments causes dielectric breakdown which reduce the transformers function which is bad. Tesla coils fix this problem.


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Kirchhoff's current law says that the current entering any junction is equal to the current leaving that junction. The current through $R_1$ must therefore add up to the current through the three legs of the circuit. $$ I_{\mathrm{R}_1} = I_{\mathrm{cap}} + I_{\mathrm{nonlinear\ R}} + I_{\mathrm{R}_2} $$ Using the terms in the diagram, two of these ...


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Kirchhoff's Voltage Law states that the voltage around a closed mesh or loop is zero. In this case, taking an 'imaginary loop current', $i$ around the 'central' mesh in your circuit, you get: $$v_c(t)-v_{R2}(t)-v_L(t)=0$$ where $v_{R2}(t)$ and $v_L(t)$ are the voltage drop across the variable resistor $R_2(t)$ and inductor $L$, respectively. I'll leave ...


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The light from a fluorescent lamp is produced by an electric current discharging through a gas, typically mercury vapour, which releases photons in the UV-range. These are then absorbed by a thin phosphor coating on the inside of the glass tube, which re-emit a photon in the visible spectrum. In order to generate the required voltage and maintain an arc ...


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It is common knowledge that electrons are mobile and therefore used in conductivity. Electrons move freely within the structure of an atom but protons are bound in the nucleus and therefore immobile. Conductivity will therefore occur when electrons move from one atom to another and not protons due to their immobility. We now learn particles are involved in ...


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To increase the current in the circuit, more and more cells are connected in the circuit. cells in parallel reduces the total resistance of the circuit.


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I have never heard about an energy field. However, I see two things. First, what causes the energy transfer : the two terminals of the battery have different potential. This means that the electrons will try to go from the - to the +. If they are allowed to do so (if there is a wire), the difference of potential tends to decrases, and the chemical reaction ...


0

The "whole" electricity will not travel through the whole network. First of all, on a big network, the common physical quantity if the frequency. The voltage is also shared, but may fluctuate locally (geographic viewpoint) depending on reactive power consumption/production. However, even if the voltage is overall constant, you can draw the flux of energy ...


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Okay, in the first place, this is not really a trivial topic, it's an entire subtopic of electrical engineering. But in this case it should suffice to say, that in ordinary conductors, you have resistive losses, they're not ideal. You can find that the entire resistance of a grid element is proportional to the inverse of its cross-section and to its length. ...



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