What is Direct current: Definition and 35 Discussions

Direct current (DC) is the one directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or even through a vacuum as in electron or ion beams. The electric current flows in a constant direction, distinguishing it from alternating current (AC). A term formerly used for this type of current was galvanic current.The abbreviations AC and DC are often used to mean simply alternating and direct, as when they modify current or voltage.Direct current may be converted from an alternating current supply by use of a rectifier, which contains electronic elements (usually) or electromechanical elements (historically) that allow current to flow only in one direction. Direct current may be converted into alternating current via an inverter.
Direct current has many uses, from the charging of batteries to large power supplies for electronic systems, motors, and more. Very large quantities of electrical energy provided via direct-current are used in smelting of aluminum and other electrochemical processes. It is also used for some railways, especially in urban areas. High-voltage direct current is used to transmit large amounts of power from remote generation sites or to interconnect alternating current power grids.

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  1. J

    Why a DC (direct current) component is undesirable?

    When choosing Line Codes (e.g. Bipolar or Polar formats) for transmission of bits over a communication channel such as twisted pairs, it is always desirable that no DC component is present for a particular choice. According to William Stallings (Digital Communication Book) "With a dc component...
  2. hackhard

    Detect current direction in water

    a bowl is filled with tap water .electric current is made to flow due to electrodes attached to rim of bowl(opposite sides of bowl) i have 2 sense pins inserted into the water between the electrodes . how can i convert this analog signal(vd across sense pins) to a digital signal to detect...
  3. H

    Direction of rotation of a direct current motor

    Homework Statement I recently made a direct current motor with a battery and a magnet. Is it possible for the coil to move in both directions without changing the current or magnetic field? If so, why might the motor work better in one direction? Homework Equations F= BIL The Attempt at a...
  4. M

    Splitting 12V high current DC wire

    A large number (56) of 18 gauge-ish connection pins are presented by the connector. They are wired together in large groups on the "client" side of the connector (4 electrodes). We wish to re wire these groups together and then split them off into 24x 18 AWG a few feet removed from the...
  5. C

    Understanding Electron Flow in Direct Current

    I don't get DC. How do the electrons flow from one side to the other? Wouldn’t the electrons on both terminals just meet in the middle because of their attraction?
  6. KingDaniel

    Varying Direct Current and Alternating current

    Homework Statement I've been struggling to fully understand the difference between Varying Direct Current and Alternating Current. Please explain this to me. Also, how would they differ on a Current-Time graph? Homework Equations E = int (VI dt) The Attempt at a Solution
  7. P

    Power dissipated by a resistor in a circuit

    Homework Statement Homework Equations P = V^2 / R 1/Rt = sum(1/Ri) (parallel) The Attempt at a Solution [/B] Since all the answer choices express the solution in terms of V^2 / R, I tried to find the voltage drop across resistor #2 to find the power. I collapsed the two parallel...
  8. P

    Potential difference across two points in a circuit

    Homework Statement [/B] Find the potential difference between points b and a in the circuit below I have already solved for the voltages of the two batteries (1 and 2) in the circuit (18 V and 7 V respectively) 2. Homework Equations Kirchhoff's Rules 1) Potential difference across any...
  9. N

    How to Activate Relay using Transistor?

    The title already said the question of this thread. As I searched the internet, transistors were configured in common-emitter configuration. They also show me that in order to activate the relay, the transistor should be operated in saturation and cut-off mode. How to make my BC547 Transistor...
  10. N

    Follow-up question about my understanding on rectification

    I understand the process of rectification but just only in theory. But I still have questions that I guess will be answered if I can experience or has experience about it (but sadly I don't have). Please kindly answer these questions: 1. Does the waveform of Vout can be considered as DC (...
  11. AdityaDev

    DC power supply

    How do i get 250v dc power supply?? Should I use lots of batteries or is there an easier way?
  12. S

    Direct Current Circuits

    Homework Statement 10) A voltmeter whose resistance is 1000Ω measures the voltage of a worn-out 1.5V flashlight batter as 0.9V. What is the internal resistance? 11) If the flashlight battery of the preceding problem had been measured with a voltmeter with a resistance of 10MΩ what voltage...
  13. F

    Considering a short parabolic impulse as direct current?

    Is it possible to consider a short (20ns) impuls of only one polarity as a short segment of direct current in a simple circuit where the reflections are to be analyzed? If not, how should I treat this kind of voltage waves? The voltage is obviously not constant, but I wonder if it is possible...
  14. D

    Puzzled about direct current and charge (flux)

    This is a question that has kept me awake, trying to rationalise it: Current is rate-of-change-of-flux (or charge if you prefer, which is the same thing): i = dQ/dt Therefore, flux or charge is the time integral of the current. Q = ∫i dt Therefore, if you have a direct current, does...
  15. L

    Alternating current and Direct current?

    I have this Question about toaster and electric kettle and I just want to know if they are working on alternating current or direct current. Does a Toaster works on alternating current or direct current? and why? Does a electric kettle runs on alternating current or direct current? and...
  16. V

    What does it mean variable Direct Current ?

    what does it mean "variable Direct Current"? I am confused on the point where i see the word variable DC in a question(see attachment). If a DC vary like a curve then in some cases it can be like AC. How is it varying (Don't tell me answers.)
  17. P

    Direct current in electric motors?

    1. Small electric motors with only one armature loop sometimes get stuck. They can be started again by giving the armature a small twist. Looking at the diagram below, what might be the explanation for the motor not being able to start on its own? When the brush(es) reaches the split within...
  18. T

    What is the minimum pulse width for switching a DC voltage/current?

    Hi guys. I recently posted to discuss on switching signals. I have resolved that. Now, I am trying to switch a DC voltage/current. Say I am supply a DC stable bias current of about 40 mA. If I want to switch it off at certain time interval, maximum of 40 us. Which means, the maximum...
  19. B

    On/Off Alternating Direct current other than a power switch?

    Hello, I would like to know if there is a part I can buy that will alternate my dc power circuit on/off at short intervals automatically All help much appreciated, Cheers, Nick
  20. V

    Increase the distance between plates of a capacitor in direct current

    Hi. I've been studying in details how a microphone works. I've found a type of microphones where capacitor is used to record sound. The idea is simple. Increasing and decreasing the distance between the plates of a capacitor (sound waves) results in the changing capacitance. Being connected...
  21. S

    Direct current brain stimulation improves motor skills

    A recent study has shown that non-invasive anodal transcranial direct current stimulation (tDCS) over the primary motor cortex can improve certain newly taught motor skills and those skill gains are retained after 3 months adjusted for time related declines in both treated and control (sham)...
  22. I

    Steady direct current question

    I have a question (possibly dumb) if someone could humor me with an explanation . I understand that steady currents don't create electromagnetic radiation. If that's true how does a high-voltage steady DC current create interference? For that matter why does a high voltage capacitor create...
  23. G

    Direct Current circuits

    Homework Statement What is the equivalent resistance of the combination of identical resistors between points a and b in the figure below?Homework Equations Series= Req= R1 + R2 + R3 etc Parallel = Req= (1/R1 + 1/R2 + 1/R3 etc)^-1The Attempt at a Solution Req= R1 + (1/3R) + R3 I don't know...
  24. T

    Question on Direct Current Drives

    Homework Statement A seperately excited 200V DC motor is driven by a single quadrant chopper receiving a 20kHz pwm signal. It is operating on 350 V DC input. Its Armature resistance and inductance are 0.5 ohm and 5mH respectively and has a torque constant k=1.5 Nm/A. Homework Equations...
  25. T

    High voltage Direct Current

    Happy holidays everyone! I'm searching how to produce high voltage, high current DC electricity to be used for statically charging a giant electroscope. The explanation why is very elaborate, so to put it simply, I need to energize a giant electroscope. I have limited electrical...
  26. J

    Why can't transformers work with direct current?

    A transformer consists of a conductor (often times can be an iron core), which is used to transfer current/voltage from one circuit (sometimes power lines) to another circuit (homes- often referred to as "stepping down"). This is done by taking a wire connected to the first circuit and wrapping...
  27. M

    Calculating Current in a Direct Current Circuit with Kirchhoff's Rules

    I have a problem solving the following direct current circuit: The Resistor-values are know, as is the ems. The question is to define the current in each part of the circuit. I thougth of solving it with kirchhoff rules, and therefore I defined several currents. (I, A-> E) I set up...
  28. B

    Direct Current Circuits and automobile battery

    1.An automobile battery has an emf of 12.6 V and an internal resistance of 0.0620 . The headlights together present equivalent resistance 6.00 (assumed constant). What is the potential difference across the headlight bulbs when they are the only load on the battery? What is the potential...
  29. H

    Alternating current versus direct current

    i am currently going over ac and dc currents in school but i want to know more but my teacher isn't going very deep into this subject. Can you help me out please?
  30. Z

    What is the meaning of the \sum signal in this direct current circuit problem?

    I've attached the problem in this post, so that's way yall can see the problem and picture easily. The Attempt at a Solution what is this signal \sum means in the problem? THe problem said they find the ammeter in the cirucuit read 2A, I just wonder is it the total current? If i set up...
  31. I

    Direct Current Circuit with Galvanometer.

    [SOLVED] Direct Current Circuit with Galvanometer. Homework Statement http://img299.imageshack.us/img299/6357/document002aa5.jpg [Broken] Homework Equations V = IR The Attempt at a Solution http://img263.imageshack.us/img263/6684/document003kl5.jpg [Broken] I did the...
  32. S

    Why doesn't direct current exhibit self-induction?

    Ok, I reformed my question, and I will be very happy if you answer me. I know that the electrons have magnetic field. So if the electrons are moving through a conductor (in direct current) than logically the magnetic field will move also. So there will be also self-induction. Can you give me...
  33. T

    Electric current and direct current circuits

    I seem to be having a problem getting this. I can get the first question, it is .65 A. But I can't seem to figure out the potential at point B. I used Vab = I2 * I1 but it still doesn't work.
  34. G

    Alternating Current vs Direct Current

    Can someone explain breifly or in detail :biggrin: the differnece between ac and dc. Maybe advantages and disadvantages. From what i have researched i know that ac the current flows in every direction while in dc it only flows in one. In ac the voltage can be put down and up using transformers...
  35. B

    Direct Current Circuits and Kirchoff's rules

    Im having a bit of trouble with some problems using Kirchoff's rules. The problem states for me to calculate each of the unknown currents: I1, I2, & I3 for the circuit diagram attached. Now I've drawn my diagram and I've gotten my three equations for three unknowns, but i keep getting a...
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