What is Junction: Definition and 223 Discussions

A junction, in the context of rail transport, is a place at which two or more rail routes converge or diverge. This implies a physical connection between the tracks of the two routes (assuming they are of the same gauge), provided by points (US: switches) and signalling. Junctions are important for rail systems, their installation into a rail system can expand route capacity, and have a powerful impact upon on-time performance.

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  1. E

    Mechanically controllable break junction electrodes

    Hi all :) There are some questions troubling me concerning mechanically controllable break junction electrodes. Generally, what happens is the bridge between the electrodes is opened by bending. At a certain point the bridge is broken and the two sharp electrodes are formed. So, my questions...
  2. K

    P-n junction diodes (Both bias)

    Given this picture, the circuit is put in reverse bias. Therefore the electrons are flowing INTO the p-type junction. - As electrons flow into the p-type material the depletion zone is raised as the p-side is made more negative. A picture from hyperphyics.phy-astr.gsu.edu illustrates this...
  3. D

    P-n junction in a thermoelectric device

    Greetings, I've just learned some of the basics about thermoelectrics, and I often come across a diagram that confuses me (see the third and fourth figures in the http://en.wikipedia.org/wiki/Thermoelectric_effect#Charge-carrier_diffusion"). All of the literature I've read refers to the top...
  4. S

    Full-Wave Rectifier w/ 2 P-N Junction Diodes & Transformer

    Show how two P-N junction diodes can be used in conjunction with a transformer that has two secondary windings, to form a full-wave rectifier. (Draw a circuit diagram including connections to the mains transformer). Explain the operation of your circuit using sketches of waveforms. (3 marks)...
  5. S

    Bjt npn base collector junction breakdown

    When the NPN is in the forward active mode The base emitter junction is forward biased and the base collector junction is reverse biased. But isn't it possible for the base collector junction to break down? Or do we assume it never breaks down? Also does anyone know any good water analogies...
  6. PainterGuy

    P-N Junction: connecting P-side to -ive terminal and N-side to +ive terminal

    hi everyone, i have discussed this problem with some other people but couldn't understand it well because of my own limited knowledge and understanding of such things. then i sent an email to my very dear teacher and a friend. email copy and my teacher's reply is below. now the problem is i...
  7. J

    Concentration of minority carriers in a pn junction

    Homework Statement A semiconductor p-n junction is fabricated where the doping concentration on the p and n sides of the junction is Na=1E18cm^-3 and Nd=1E16cm^-3 respectively. Given that ni=1.18E10cm^-3, T=300k calculate: a) The majority and minority carrier concentrations in the...
  8. S

    Pn - junction diode experiment - varying heat

    Homework Statement This isn't exactly a problem, but I need help with an experiment. I've got to design an experiment to show a) the variation of voltage with a diode when the diode is in forward bias b) The variation of current (i think) with heat, keeping voltage constant. The thing is...
  9. M

    Traffic Flow - Junction, Delay, Webster, Greatest Upper Bound

    [PLAIN]http://img96.imageshack.us/img96/7816/12530747.jpg Hopefully this will post successfully... Erm its the first part I'm not sure on, after that it's easy. I'm just not understanding the wording. I need to work out the effective green time during the cycle
  10. S

    PN Junction open conditions conservation of energy

    When a PN juction is in the open circuit condition, my textbooks says the following. "The voltage measured between the terminals is zero. That is the junction Voltage Vo does not appear across between the diode terminals.This is because of the contact voltages existing at the...
  11. S

    Exploring Diffusion & Drift in a Zero-Bias PN Junction

    consider we have a pn junction in zero bias. I am trying to find the equilibrium condition. As soon as a p-n junction is formed, electrons (present in conduction band) from the n-side near to the p-n interface diffuse to the p-side of the interface leaving donors in the region. Same thing...
  12. S

    Understanding the width of the depletion region in a p-n junction

    I am studying to become and electrical engineer and am currently taking Electronics I. I am having trouble understanding the change in the depletion region that results from a bias. I understand that at the time of manufacture the free electrons from the n-type semiconductor are attracted to the...
  13. P

    Why Can't P-N Junction Connected Series Act as a P-N-P Transistor?

    Hi I'm practising past papers however have no answers. one of the questions says: Why can a p-n junction connected in series with an n-p junction not act as an p-n-p transistor. My only thoughts were that the base element must be thin (approx 10 wavelengths of light) and in thus in this...
  14. K

    Questions on P-N junction circuits

    Hi I need circuit diagrams for studying P-N junction & Zener Diode under forward and reverse bias. I know they are available on Google, but I had a few questions, and if I understand the answers, I won't need circuit diagrams. 1. a) Some circuit diagrams have a rheostat connected in series...
  15. W

    Ohmic junction in Cat's-whisker detector

    Hello, I have read (wiki and physicsforums besides other sources) about how preparing an ohmic junction is hard on wafers in the clean room and that usually one gets a Schottky barrier instead, if one is not careful enough. This makes me wonder, how come that people used to get an ohmic...
  16. L

    Understanding Drift Current in a pn junction

    I'm having trouble fully conceptualizing drift current- what I always hear is that it is caused by minority carriers within one diffusion length of the junction being swept across by the electric field that is generated by the imbalance caused by diffusion of electrons. Here is what I am...
  17. 4

    What is the formula for solving a network with junction and loop rules?

    For the network shown, show that the resistance Rab = (27/17)ohms . http://www.webassign.net/pse/p28-28.gif Figure P28.28 My attempt to the problem: I got the first following equations: I1-I3-I2=0 I4+I6-I1=0 I2+I5-I6=0 I3-I4-I5=0 Note that I3 and I4 are currents flowing at the top...
  18. W

    PN junction current equation

    What are e and V in exponent of the equation I = I0(eeV/kT - 1)? is it really one variable "eV", as in electron volts, or is e just 2.718... and V for volts?
  19. O

    What determines the thickness of depletion region of a given p-n junction diodegiven

    Hello all, I am somewhat confused in understanding the depletion region of a p-n junction diode.Everywhere a depletion region is defined as a region near the p-n junction which is devoid of charge carriers.And the formation of this region is said is explain that it is due to the diffusion of...
  20. A

    Potential difference in junction of two cells one 4.5V and one 3V

    1. If two cells, one of 4.5V and one of 3V are connected in parallel what is the potential Difference across the junctions between them. 2. I = \frac{V}{R} 3. As 4.5v is greater it is the potential difference as they don't add up?
  21. M

    Current Limitation in a PN junction

    Homework Statement Describe the limiting physical mechanism for current flow in a p-n junction where there is negligible recombination in the space charge region. Write the equations that describe this current flow process. Define all parameters. a) for the general case where the junction...
  22. W

    Best pn junction book (question)

    hi all i need a book about pn junction diode that starts from 0 and goes to 100. I've been reading solid state electronic devices by Ben G Streetman and elementary solid state physics by M. Ali Omar but these are too confusing and a lot of things are not explained like how some equations are...
  23. H

    Cooling thermocouples junction

    please let me know how to cool the junction of thermocouple... is it possible to give current to both the wires n get junction cooled...?
  24. H

    Can Thermocouple Junctions Cool Down When Supplied with Current?

    is it possible that instead of heating the junction ... of thermocouple... we supply the current n the juntion cools down... which when touched felt cold... according to the supply of current...?? if not then is there any method of doing that
  25. N

    V_n equaion question on PN junction

    the formula for Vn should be V_n=(E_f-E_i)/q field divided by charge in the potential like i was taught in high school but why the write it V_n=(E_f-E_i)/KT k in the boltsman constant t is the temprature there multiplication cannot be the charge ?
  26. A

    Understanding the Junction Rule for Circuit Analysis

    Homework Statement I need to find the current equation for the junction in node a in the following circuit: http://i749.photobucket.com/albums/xx137/abcdmichelle/gjgjhg.jpg Homework Equations Current in = Current out so I(in)=I(out) The Attempt at a Solution The arrows in the...
  27. T

    P-N Junction Diode Problem HELP

    Homework Statement A pn junction diode has saturation current Is= 1e-12 A. What is the current through this diode if a positive voltage 0.68 V is applied to it? (Unit: A) Homework Equations I=Is(e(Vd)/(Vt))-1) The Attempt at a Solution I don't even know where to begin, but i just...
  28. R

    P-n junction diode open circuit electric field

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  29. S

    Potential energy vs. fermi level in metal-metal junction under applied field

    Hello, I have been lurking in the forum for a while. I have couple of questions that I cannot really find an answer to yet. If any of you have idea/suggestion/know of where to look at, I would greatly appreciate. First question: Let's put two different work function metal blocks to each...
  30. H

    Figuring Out Current Above the Junction: A Puzzling Problem

    Homework Statement In the figure, what is the current in the wire above the junction? Homework Equations V=IR or I=V/R The Attempt at a Solution I am really confused as to what "above the junction" means. I tried to add the voltages and add the resistors and divide them to get...
  31. A

    Metal-Semiconductor Junction

    Hi, I have a questions regarding semiconductor-metal junctions that has been left unresolved. I hope that you can offer me an explanation. I know that when a metal and n-doped semiconductor are in contact upward band bending occurs. This is because the Fermi levels in the two materials...
  32. C

    Bipolar Junction Transistor - Saturation

    Hello All, I have very basic questions with respect to what we mean when we say a Transistor is in "Saturation". As I have read almost everywhere, we need to Forward bias both the emitter-base junction and Collector-Base Junctions for transistor to go to Saturation. Before I post my...
  33. A

    Air's Bipolar Junction Transistor Q&A Thread

    Hi, I'm learning Bipolar Junction Transistor and need help to confusion which arise so I will keep posting questions which I don't understand to this thread. Thank you in advance. So my questions start: When using hybrid pi model and t model, we determine the dc operating point first. In one...
  34. A

    Are These Two BJT Circuits Equivalent?

    I've got these two BJT circuits. I want to know if the result are the same. Are both circuits below same? Can the bottom left resistor be grounded and be same as the second circuit. http://img21.imageshack.us/img21/2886/bjtt.jpg
  35. C

    Semiconductor and p-n junction questions

    Hi guys, I just have a few questions regarding semiconductors and p-n junctions. How can I explain using an E vs k diagram why a silicon based device can be an efficient light detector but not an efficient light emitter? I imagine it has something to do with the fact that an electron in the...
  36. S

    Exploring the Effects of Two Differing Donor Concentrations in a Junction

    Hi, If we had two junctions one side with Nd=1016 & another side with Nd=1015 put together. What happens in such a junction? Would we see electron diffusion from the high donor concentration side to the lower concentration side? What should the band diagram of the junction look like...
  37. U

    P-N junction - Need explanation

    "...Recall that the n-side is studded throughout with positively charged donor ions, fixed firmly in their lattice sites. Normally, the excess positive charge of each of these ions is compensated electrically by one of the conduction band electrons. When an n-side electron diffuses across the...
  38. R

    Forward resistance of the Base -Emmiter Junction?

    Homework Statement Forward resistance of the Base -Emitter Junction showed a value of 12ohms when it was measured by (x1) resistance scale of an analogue multimeter .And it showed 70ohms when it was measured using (x 10) scale factor .The variation in the two readings occurs due to...
  39. A

    Turn-on voltage of pn junction diodes

    Hey, I am working on a report and got stuck at two discussion questions. Help & discussion would be greatly appreciated! 1. What factors determine the turn-on voltage of a pn junction diode? Explain its dependence on the factors you mentioned My guess would be that the light intensity on...
  40. J

    Junction Potential: Nichrome Wires of Different Lengths & Areas

    Homework Statement One end of a nichrome wire of length 2L and cross-sectional area A is attached to an end of another nichrome wire of length L and cross-sectional area 2A. If the free end of the longer wire is at an electric potential of 8.0 V, and the free end of the shorter wire is at an...
  41. A

    Why in MOSFETs Halo doping is done near source and drain junction only?

    Somewhere I read that the reason of halo doping in the MOSFETs is to increase the average doping of channel as the channel length is scaled to lower values. But I think there should be more about why is it done only at the source drain junction, and not somewhere else randomly like at the...
  42. L

    Pn Junction Diode: Electrons, Holes, and Immobile Ions

    folks, when a pn junction diode is formed, electrons in the n type and holes in the p type diffuse. agreed. then how immobile ions are formed at the vicinity of the junction leading to depletion region? how these immobile ions prevent further diffusion? it is being said electrons and holes...
  43. M

    Boundary condition at junction of heated rods

    1. 1D heat conduction problem: Two rods, the first of length a , the second of length L-a with respective cross sectional areas A_1 , A_2 and heat conductivities k_1 , k_2 , are joined at one end. There are some boundary conditions on the other ends of the rods, but my question is only...
  44. R

    Pn junction in solar cell case

    HI. I got some question about the derivation of the I-V characteristic in a solar cell. The first step is to solve the minority carrier diffusion equation with appropriate boundary conditions: at the edges of the cell and at the edges of the depletion zone. At the edges of the d.z. the...
  45. R

    Finding reverse sat current of pn junction diode

    Homework Statement Determine reverse sat current of diode. To show and explain approach. Given-IV characteristics of diode and tabulated values for forward bias voltage from 0-0.8v and corresponding current values. Homework Equations At which point do I need to consider to find the...
  46. E

    Understanding Band Bending at Metal-Semiconductor Junctions

    Hi everyone. Is there anyone that can explane the band bending, whiche takes plane when a metal and a semiconductor are joined together? In illustrations of the band bending, it looks like that the energy of the valence and conduction band far from the junction have been lowered or raised...
  47. DaTario

    How do diodes (pn junction) work?

    Hi all, I would like to know how pn junction work? thanks DaTario
  48. C

    Solve 5 Wire Junction Current w/ Conservation of Current

    Homework Statement The information about the magnitudes of the current density and the diameters for wires 1, 2, 3, and 4 is given in the table. Some of the values are unknown. Wire Current density (A/mm^2) Diameter (mm) Total Current (A) 1-------- 1.6 --------...
  49. L

    Understanding the Function of a PN Junction Diode | Explained by Experts

    Say we have a silcon pn junction (diode) - i.e., a block of p-type on left, attached to a block of n-type semiconductor on right: anode ------[ p | n ]------ cathode Because of diffusion we get a barrier potention at the junction, which makes the n-side/cathode 0.7V higher...
  50. P

    Internel potentiel of PN junction? so complicated

    internel potentiel of PN junction?? so complicated homojunction PN (not polarized), externel potentiel difference applied = 0 Volt . i should demonstrate the equation: e*Vbi + Eg + ( Ec - Ef ) + ( Ef - Ev) = 0 Given: Vbi= internel potential Eg= energy gap Ef = Fermi...
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