question: since electricity can only travel in a closed circuit, how does it know that the circuit is closed if it hasn't "travelled" there?
comment: It follows the "path of least resistance". Think of electrons like cars crowded in a parting lot after a concert. They all want to go home, but they can all see a car right in front of them. When one car leaves the lot, it makes a little open space, and another car fills it. All they have to do in move into an open space, they don't need a long term view of the circuit and their ultimate path to the sink. They are electrons, not as clever as people.
passages: The TES is voltage-biased by driving a current source "I" through a load resistor "R" (see figure). The voltage is chosen to put the TES in its so-called "self-biased region" where the power dissipated in the device is constant with the applied voltage. When a photon is absorbed by the TES, this extra power is removed by negative electrothermal feedback: the TES resistance increases, causing a drop in TES current; the Joule power in turn drops, cooling the device back to its equilibrium state in the self-biased region. In a common SQUID readout system, the TES is operated in series with the input coil "L", which is inductively coupled to a SQUID series-array. Thus a change in TES current manifests as a change in the input flux to the SQUID, whose output is further amplified and read by room-temperature electronics.
   Maxwell, looking further than Faraday, reasoned that if light is an electromagnetic phenomenon and is transmissible through dielectrics such as glass, the phenomenon must be in the nature of electromagnetic currents in the dielectrics. He therefore contended that in the charging of a condenser, for instance, the action did not stop at the insulator, but that some "displacement" currents are set up in the insulating medium, which currents continue until the resisting force of the medium equals that of the charging force. In a closed conductor circuit, an electric current is also a displacement of electricity.
   The conductor offers a certain resistance, akin to friction, to the displacement of electricity, and heat is developed in the conductor, proportional to the square of the current(as already stated herein), which current flows as long as the impelling electric force continues. This resistance may be likened to that met with by a ship as it displaces in the water in its progress. The resistance of the dielectric is of a different nature and has been compared to the compression of multitudes of springs, which, under compression, yield with an increasing back pressure, up to a point where the total back pressure equals the initial pressure. When the initial pressure is withdrawn the energy expended in compressing the "springs" is returned to the circuit, concurrently with the return of the springs to their original condition, this producing a reaction in the opposite direction. Consequently, the current due to the displacement of electricity in a conductor may be continuous, while the displacement currents in a dielectric are momentary and, in a circuit or medium which contains but little resistance compared with capacity or inductance reaction, the currents of discharge are of an oscillatory or alternating nature.
   To test or remove a particular printed circuit card from service, there is a well-known algorithm. As fewer connections pass through the card's subswitch, the software routes more test signals through the subswitch to a measurement device, and then reads the measurement. This does not interrupt old calls, which remain working.
   Section::::Representative circuit.
  
  The circuit diagram illustrates a simple ground loop. Two circuits share a common path to ground. This path has a resistance of formula_1. Ideally, the ground conductor would have no resistance (formula_2), yielding no voltage drop across it, formula_3, keeping the connection point between the circuits at a constant ground potential. In that case, the output of circuit 2 is simply formula_4.
   The sensor circuit is supplied with constant current. A distinguishing feature of the IEPE principle is that the power supply and the sensor signal are transmitted via one shielded wire.
   The language itself can be seen as a set of connections between logical checkers (contacts) and actuators (coils). If a path can be traced between the left side of the rung and the output, through asserted (true or "closed") contacts, the rung is true and the output coil storage bit is asserted (1) or true. If no path can be traced, then the output is false (0) and the "coil" by analogy to electromechanical relays is considered "de-energized". The analogy between logical propositions and relay contact status is due to Claude Shannon.
   Because the bus lines are electrically open collector it works like a long OR gate between all device line drivers. The logical value for ground is true and vice versa. Any device may set a line "true". A line only becomes "false" if all devices signal false.
   BULLET::::- The current in typical electric circuits is confined to the circuit, with very little "leakage". In typical magnetic circuits not all of the magnetic field is confined to the magnetic circuit because magnetic permeability also exists outside materials (see vacuum permeability). Thus, there may be significant "leakage flux" in the space outside the magnetic cores, which must be taken into account but often difficult to calculate.
   General communication with a specific fixture occurs in a request-response pattern. The controller sends the request to the device, addressing it by the device's UID. When the request has been sent, the controller relinquishes control of the DMX line for a given period of time, so the device can transmit its response. Unicast communication is the only way in which data can be retrieved from a fixture (other than its UID which can be obtained using the discovery mechanism mentioned above). If the device does not respond within a given period of time, the controller can assume communication has failed, and may retry.
   The master starts a transmission with a "reset" pulse, which pulls the wire to 0 volts for at least 480 µs. This resets every slave device on the bus. After that, any slave device, if present, shows that it exists with a "presence" pulse: it holds the bus low for at least 60 µs after the master releases the bus.
   The basic principle is shown in Fig. 1, in which individual particles suspended in fluid flow one-at-a-time through a micro- or nanoconstriction. The fluid is weakly conducting, and the obscuration of an electrical sensing current flowing through the fluid by the presence of the particle causes an increase in the measured voltage, in other words, the particle causes a change in the electrical resistance of the nanoconstriction. This is shown schematically in Fig. 2.
   Leaking pipes: The electric charge of an electrical circuit and its elements is usually almost equal to zero, hence it is (almost) constant. This is formalized in Kirchhoff's current law, which does not have an analogy to hydraulic systems, where the amount of the liquid is not usually constant. Even with incompressible liquid the system may contain such elements as pistons and open pools, so the volume of liquid contained in a part of the system can change. For this reason, continuing electric currents require closed loops rather than hydraulics' open source/sink resembling spigots and buckets.
   The most common way to determine whether a section of line is occupied is by use of a track circuit. The rails at either end of each section are electrically isolated from the next section, and an electrical current is fed to both running rails at one end. A relay at the other end is connected to both rails. When the section is unoccupied, the relay coil completes an electrical circuit, and is energized. However, when a train enters the section, it short-circuits the current in the rails, and the relay is de-energized. This method does not explicitly need to check that the entire train has left the section. If part of the train remains in the section, the track circuit detects that part.
   A track circuit typically has power applied to each rail and a relay coil wired across them. When no train is present, the relay is energised by the current flowing from the power source through the rails. When a train is present, its axles short (shunt) the rails together; the current to the track relay coil drops, and it is de-energised. Circuits through the relay contacts therefore report whether or not the track is occupied.
   First we have the normally open, timed-closed (NOTC) contact. This type of contact is normally open when the coil is unpowered (de-energized). The contact is closed by the application of power to the relay coil, but only after the coil has been continuously powered for the specified amount of time. In other words, the direction of the contact's motion (either to close or to open) is identical to a regular NO contact, but there is a delay in closing direction. Because the delay occurs in the direction of coil energization, this type of contact is alternatively known as a normally open, on-delay.
   When a device is first attached to a switch port, it will not immediately start to forward data. It will instead go through a number of states while it processes BPDUs and determines the topology of the network. When a host is attached, such as a computer, printer or server, the port always goes into the forwarding state, albeit after a delay of about 30 seconds while it goes through the listening and learning states (see below). The time spent in the listening and learning states is determined by a value known as the forward delay (default 15 seconds and set by the root bridge). However, if instead another "switch" is connected, the port may remain in blocking mode if it is determined that it would cause a loop in the network. Topology Change Notification (TCN) BPDUs are used to inform other switches of port changes. TCNs are injected into the network by a non-root switch and propagated to the root. Upon receipt of the TCN, the root switch will set a Topology Change flag in its normal BPDUs. This flag is propagated to all other switches to instruct them to rapidly age out their forwarding table entries.
   RCDs operate by measuring the current balance between two conductors using a differential current transformer. This measures the difference between current flowing through the live conductor and that returning through the neutral conductor. If these do not sum to zero, there is a leakage of current to somewhere else (to earth/ground or to another circuit), and the device will open its contacts. Operation does not require a fault current to return through the earth wire in the installation; the trip will operate just as well if the return path is through plumbing, contact with the ground or any other current path. Automatic disconnection and a measure of shock protection is therefore still provided even if the earth wiring of the installation is damaged or incomplete.
   In NOR gate flash, each cell resembles a standard MOSFET, except the transistor has two gates instead of one. On top is the control gate (CG), as in other MOS transistors, but below this, there is a floating gate (FG) insulated all around by an oxide layer. The FG is interposed between the CG and the MOSFET channel, and because the FG is electrically isolated by its insulating layer, any electrons placed on it are trapped there and, under normal conditions, will not discharge for many years. When current flow through the MOSFET channel binary code is generated, reproducing the stored data.
   Early attempts to solve the two-pulse measurement problem were made by Trebino and Kane and co-workers beginning in 1995. They took advantage of the fact that FROG and its variations involved crossing two replicas of the pulse to be measured in a nonlinear-optical medium (where one gated the other in time) and measuring the spectrum of the product of the two pulse electric fields vs. delay. Thus, instead of using a known reference pulse as the gate, the second unknown pulse was used as the gate. The mathematical form of the measured trace is
   Scientists working with high vacuum systems test for the presence of tiny pin holes in the apparatus (especially a newly blown piece of glassware) using high-voltage discharges produced by a small handheld Tesla coil. When the system is evacuated the high voltage electrode of the coil is played over the outside of the apparatus. At low pressures, air is more easily ionized and thus conducts electricity better than atmospheric pressure air. Therefore, the discharge travels through any pin hole immediately below it, producing a corona discharge inside the evacuated space which illuminates the hole, indicating points that need to be annealed or reblown before they can be used in an experiment.
   A digital current loop uses the absence of current for high (space or break), and the presence of current in the loop for low (mark). This is done to ensure that on normal conditions there is always current flowing and in the event of a line being cut the flow stops indefinitely, immediately raising the alarm of the event usually as the heavy noise of the teleprinter not being synchronized, something that would not have been possible if the idle state had been no current flowing.
  
  Section::::Electrical characteristics.
   Wireless powerline sensor
  
  A Wireless powerline sensor hangs from an overhead power line and sends measurements to a data collection system. Because the sensor does not contact anything but a single live conductor, no high-voltage isolation is needed. The sensor, installed simply by clamping it around a conductor, powers itself from energy scavenged from electrical or magnetic fields surrounding the conductor being measured. Overhead power line monitoring helps distribution system operators provide reliable service at optimized cost.
  
  Section::::Communication.
   The monitoring device switches off the transmitter when the antenna shows incorrect behavior, e.g. as a result of undesired electrical charge. When the transmitter is switched off, these charges dissipate. The monitoring device makes several attempts to switch back on. If after several attempts the antenna continues to show improper behavior, possibly as result of structural damage, the transmitter remains switched off.
  
  Section::::Structure protectors.:Lightning conductors and grounding precautions.
   If a current "I" from a separate source is flowing through the ground conductor, the resistance "R" of the conductor will create a voltage drop along the cable ground of "IR", so the destination end of the ground conductor will be at a different potential than the source end 
  
  Since the differential amplifier has high impedance, little current flows in the signal wire, therefore there is no voltage drop across it: formula_15 The ground voltage appears to be in series with the signal voltage "V" and adds to it
  
presuppositions: Due to electricity traveling in a closed circuit, it should not be able to know if a circuit is closed without traveling to it. Because electricity only travels in a closed circuit, it is not probable for the circuit to know if it is closed if it hasn't traveled there yet.
corrections: Electricity follows the path of least resistance. Electricity follows the path of least resistance.
raw_presuppositions: Due to electricity traveling in a closed circuit, it should not be able to know if a circuit is closed without traveling to it. Because electricity only travels in a closed circuit, it is not probable for the circuit to know if it is closed if it hasn't traveled there yet. Electricity can only travel in a closed circuit.
raw_corrections: Electricity follows the path of least resistance. Electricity follows the path of least resistance. Electricity follows the path of least resistance.