# What is Dc circuit: Definition and 105 Discussions

A DC-to-DC converter is an electronic circuit or electromechanical device that converts a source of direct current (DC) from one voltage level to another. It is a type of electric power converter. Power levels range from very low (small batteries) to very high (high-voltage power transmission).

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1. ### Resonance of a PWM DC Circuit

I am experimenting with finding the resonant frequency of water in an attempt to disassociate the H2O bond without high voltage/current and using just tap water - no electrolytes, etc. I know how it works in classic electrolysis but that's not what I am attempting. Assume that there is a...
2. ### Why is it important to classify circuits as series or parallel?

The answer sheet assumes that the resistors in both circuits are in series and that we need to use the equation Req = R1+R2+R3.. to find the Req in both cases. How come the resistors are in series, when there are multiple resistors in a single row? Also, why does the following work yield the...
3. ### Power dissipated in this circuit with 2 batteries and 3 resistors

Hi guys I am struggling to find the power dissipated in the total circuit , my answer didn't match the solution in the book the circuit is simple i used Kirchhoffs rules to find the following : loop 1 : $$10-10I_{1}-40I_{3} = 0$$ loop 2: $$20-20I_{2}-40I_{3} = 0$$ and $$I_{1}+I_{2}=I_{3}$$...
4. ### Current flowing through a resistor in an RRL DC circuit

DISCLAIMER: don't answer in terms of integrals, I haven't covered those yet :) Hi guys, I'm having a few troubles understanding RRL circuits, and have a few questions for you. A "normal" RL circuit will have a current growing inversely exponentially, starting from 0 and going to ##V/R## as...
5. ### Engineering Find di/dt and dr/dt for a DC circuit with indepedent current source

Dear PF, I am trying to solve practice problem 8.2. I am stuggling with part B of the question which asks us to find diL(0+)/dt, dvC(0+)/dt and dvR(0+)/dt. My attempt can be seen below. Before t=0 the 4A current source is not present and thus it is an open circuit. A capacitor acts as an open...
6. ### A question about an electron’s movement in a DC circuit

I have been thinking of the nature of the electric current , or the motion of electrons in a copper cable of a closed DC circuit. Recently I learned the speed of electron is very slow in the copper cable and in a AC circuit the FREE ELECTRONS are in fact moving back and forth. But in a DC...
7. ### Maximum voltage that can be applied to DC circuit with resistors

I see that ##V_{ac}=V_{ab}+V_{bc}##, with ##V_{ab}=I_1R_1=I_2R_2## and ##V_{bc}=I_3R_3##. However, I don't see how to express mathematically the maximum value of ##V_{ac}##. Could someone please help me with this task?
8. ### Wheatstone Bridge: Substitution Resistance Formula Derivation?

Hello, In high school, I had been taught about finding substitution resistance from Wheatstone bridge. The formula: a. If the cross product of ##R1## and ##R3## is same as ##R2## and ##R4##, the galvanometer in the middle (##R_5##) can be omitted and use series-parallel principle to solve for...
9. ### Engineering DC bias current and small-signal resistance

We are given that ##i_D = 8\cdot 10^{-12} (e^{v_D/20m} - 1)## Hence ##i_D' = e^{50 v_D}/2500000000## and ##i_D'' = e^{50 v_D}/50000000## Then I have that ##\delta i_D \approx\frac{ e^{50 v_D}}{2500000000} \cdot \delta v_D = \delta v_D / 5## Cancelling ##\delta v_D## from boh sides and solving...
10. ### Nodal Analysis Problem help (Double Supermesh)

That is, for Supernode -1,3 (12V branch) , we do Nodal Analysis and we have (V2-V3)/2 , over the 2 ohm branch. But this current is not included in the Equation 1 in the solution I have attached(Which is my only source to cross check answers/solution right now.) Is the solution wrong? Thanks...
11. ### How to use Thevenin to find R and I?

Homework Statement In the circuit shown, in the image, the variable resistor R is consuming maximum power. Determine: a) resistance for R b) power for R c) current for R3 and its direction Homework EquationsThe Attempt at a Solution I tried getting IA(the direction is shown with arrows in...
12. ### How to find power and voltage using the mesh current method?

Hi. I am practising for my test and since I don't have the correct answers, I don't know if what I'm doing is right. I tried to solve this problem, can you check it and correct if it's wrong? Here's a clearer picture of the circuit. I suspect Uab isn't right, but am not sure. Thanks...
13. ### Measuring the current from a micro generator affects its output?

I am performing an experiment where I have built a scale model of a wind turbine, and am measuring the current it can produce with a micro generator. I am using a standard multi meter and the micro generator is DC. I do not know much about the topic, but whenever I start measuring the current...
14. ### Unraveling the Mystery of EMF Internal Resistance

I'm having a difficult time understanding why the internal resistance of the EMF source is disregarded in this problem. 1. Homework Statement You are asked to determine the resistance per meter of a long piece of wire. You have a battery, a voltmeter, and an ammeter. You put the leads from the...
15. ### Engineering DC circuit analysis: conceptual mistake?

Homework Statement Homework Equations[/B] I have a circuit that consists on 3 components in parallel: a current source Ia, a resistor R and a capacitor C. Ia is directed upwards, while the currents through the capacitor and the resistor are both directed downwards. Select the correct option in...
16. ### Engineering Simple DC Circuit Analysis with Transistor

Homework Statement Homework Equations The Attempt at a Solution All loops are clockwise; KVL Loop around 1V, 120kOhm and VBE (I1 is assigned to the loop): -1V + 120kOhm * I1 + VBE = 0 I1 = IB = 0.3V / 120kOhm = 2.5 * 10-6 A; Loop around 10kOhm, vCE (I2 is assigned to the loop); KVL...
17. ### Initial Voltage in an RC circuit with a Current Source and no Voltage Source

Homework Statement [/B] Derive an expression for vc(t) in the circuit of Figure P4.13 and sketch vc(t) to scale versus. I attached a screen shot of the circuit for this problem. time. Homework Equations V = IR V = V0exp(-t/tau) The Attempt at a Solution [/B] I am trying to find the...
18. ### Surface Charge - Poynting Vector - DC circuit power flow

I found it very interesting to see that surface charge and the Poynting vector are being used to describe how a simple DC circuit actually works. Chabay and Sherwood have made an outstanding contribution to physics and engineering in their texts and papers. Of course others jump on the...
19. ### Voltage across an Inducter at a specific time in a DC circuit

Homework Statement Homework Equations I(t) = E/R [ 1 - e^-t/tau)] Vseries = Sum of voltages , Vparalel= V1=V2=V3... V=I*R The Attempt at a Solution
20. ### DC Circuit Analysis: Kirchhoff's Laws

1. Homework Statement A DC circuit is shown below. Note the ground (V=0) in the circuit 1- calculate the current through the 5Ω resistance. Use "+" sign for the current directed from right to left, and "-" sign if the current flows from left to right. 2- The sign of the potential at a is...
21. ### Need help with voltage across a capacitor in a DC circuit

In a RC circuit is voltage through a capacitor always consider negative no matter if you're going with or against the current when setting up a voltage equation?
22. ### Engineering DC state RC circuit Find Vc(0)

Homework Statement Find Vc(0) Homework Equations Nodal Eq , ohms law The Attempt at a Solution Can someone please check my work for Vc(0)? I'll appreciate it.
23. ### Which supercapacitor range is needed to run a 48V DC motor?

I'm doing a project where I need to hand power for dc motor (12V or 24V) and charge a super capacitor, and then use it to drive another 48V dc motor. I want to know which Super capacitor will be suitable? Please give suggestions for Super capacitor specifications for both 12V and 24V that will...
24. ### Alternatives to varistors as overload protection at DC motor

Alternatives to varistors as overload protection at DC motor DC Motor here implies 12V linear actuator w/DC Motor that consumes 2.8A under loading condition. Pretty costly equipment. I'm using a L298N motor driver connected in parallel to run the linear actuator. The motor driver is run by a...
25. ### Engineering Linear Algebra - Analysis of purely resistive DC circuit

Homework Statement I'm trying to solve this circuit when I try to simulate and run a dc sweep i get that it can't be solved. When I try to find the answer using linear algebra I get this answer after I throw it into MATLAB with the warning “[w]arning: Matrix is close to singular or...
26. ### Help With DC Circuit Questions

Homework Statement There is a current of 3.2A flowing through the 20.0ohm resistor...(the questions along with my work are attached below). I am having some trouble with DC circuits, especially those that include a combination of series and parallel circuits. I have worked through the problem...
27. ### In a DC circuit, is "negative" synonymous with "neutral"?

Hi, I'll start by offering some context to my question. I am a mechanic by trade, and have a bachelor of technology in motorsport engineering. I have a friend who is an electrician by trade, and he likes to work on his car in his spare time. In my line of work I only deal with 12V/24VDC...
28. ### Calculating voltmeter resistance in DC circuit

Homework Statement initial problem: A 228 −Ω resistor and a 586 −Ω resistor are connected in series across a 90.0−V line. A voltmeter connected across the 228 −Ω resistor reads 24.0 V . Find the voltmeter resistance. For Req, i got Req=228R/(2+228), R being the resistance of the voltmeter. But...
29. ### Is it possible to detect current ramp-up to DC with a coil?

Hi, I am thinking of ways to detect when an electrical device is turned on and off without actually touching or modifying the existing circuitry. More specifically, I have a hand held device powered by 2 x 9V batteries and with 2 electrodes connected through leads and plugs to sockets on the...
30. ### Electromagnetic Induction in a moving DC circuit

Consider a closed electric circuit consisting of a conducting straight rod connected to a DC voltage source switched on. In steady state the current flowing through the conductor creates a steady magnetic field around it with magnetic flux lines that can be represented as concentric circles...
31. ### How does surface capacitive touchscreen work in detail?

It's pretty easy to find the "working principle" of surface capacitive touchscreen like http://www.elotouch.com/Technologies/SurfaceCapacitive/howitworks.asp Roughly speaking, I know that A surface capacitive touchscreen has a conductive layer to which some electrodes are attached The...
32. ### Engineering Homework: DC circuit with capacitors

Homework Statement In the given DC circuit, while switches S1,S2 are open, conductor C1 is charged with Q10, and conductor C2 is not charged. After the switch S1 is closed, through conductors flows the amount of charge q1=40µC. After the switch S2 is closed, through conductors flows the amount...
33. ### Explanation (or Proof) for network theorems?

We started Network analysis and we were given Circuit Diagrams to be reduced using the following: Kirchoff's Laws i.e KVL and KCL Source Transformation Superposition Theorem Thevenin's Theorem Norton's Theorem and Star-Delta Conversion However I wasn't given proofs for any of these theorem...
34. ### DC Current: RA1, RA2, RA3, I1, I2, I3

Homework Statement When direct current is measured with ammeter of resistance RA1=100mΩ, current is I1=12 A. When direct current is measured with ammeter of resistance RA1=50mΩ, current is I2=15 A. What is the value of current if there is no ammeter (RA3=0)? Homework Equations Ohm's law The...
35. ### Find Range of R4 & U4 for I in [-3A,-1A]

Homework Statement Find range of resistance R4 and voltage U4 so that the range of current I is I \in [-3A,-1A] E=5V, E4=6V, Ig=1A, Ig4= -3A, R1=2ohm, R2=3ohm, R3=5ohm Homework Equations -Kirhoff's law -Potential of nodes method The Attempt at a Solution Firstly, I set current...
36. ### Change in ammeter reading due to change in resistance

Homework Statement Homework Equations 1/R= 1/R1 + 1/R2 +... I1= R2/R1 x I The Attempt at a Solution I chose B because I thought that since total resistance in the branch of variable resistor has increased, the branch with ammeter will get a greater share of current. Since I'm not too sure...
37. ### Energy flow in a DC circuit as Tsao Chang & Jin Fang see it

From the abstract: "Experiments show that Poynting vector is just a mathematical definition in the DC case. Since it does not form real energy flow, there is no transmission of electromagnetic energy flow from the exterior to the interior of a metal wire. Therefore, DC power is transmitted...
38. ### How to set the frequency of a switch in NI Multisim software

I am a new user of Multisim and I am trying to make a buck converter. In other softwares, such as pspice I was able to control the switching frequency by editing properties but in Multisim, most of the switches are user interactive. I want to set frequency of 50 Hz in a switch. Kindly help me...
39. ### Confused with circuit that has two opposing emf

Homework Statement Calculate the total power generated by G Homework Equations P=VI The Attempt at a Solution I used the P=VI formula to calculate the total power generated by G which is 40W, and the answer turns out to be correct. But actually, I don't quite understand this topic of opposing...
40. ### Engineering DC circuit analysis using Reciprocity Theorem

Homework Statement In the following circuit I need to find current I1 if the given parameters are E1=0V,E2=15V,E3=60V In the second case, given parameters are I2=100mA,I3=40mA,E1=30V,E2=E3=0V In both cases, R2=R3=R4=R5=300 ohm Homework Equations Using reciprocity theorem for DC circuits. The...
41. ### Engineering Waveform of R,L,C in DC circuit

Homework Statement Draw a time-depended waveform of all components in DC RLC circuit. R=4*1,412 L=1,6 mH C=0,2 mF Udc=15 V Homework EquationsThe Attempt at a Solution DoCircuit simulator I am a bit confussed with this homework because I am aware that capacitor do not conduct a current in DC...
42. ### Resistance and DC circuit question

Here is the problem: I have already lost the ability to get the correct answer for AI Homework Statement (a) What is the maximum potential difference that can be applied to the terminals a and b? 33.541 Which resistor will have the largest current? V (b) For the voltage determined in part...
43. ### First order RC: Find Unknown DC Circuit, given current graph

Homework Statement Homework Equations [/B] Tao = R(th) C The Attempt at a Solution The unknown DC circuit model consists of a V(th) and R(th) Tao = (R(th) + 3000) C , total resistance of circuit is R(th) + 3000 0.004 = (R(th) + 3000) (1x10^-6) R(th) = 1 kOhm The V(th) should oppose the...
44. ### Solving a DC Circuit: Find I_B, V_C, V_{CE}

Homework Statement For the circuit above, draw the DC equivalent circuit. Then compute ##I_B, V_C, V_{CE}##. Homework EquationsThe Attempt at a Solution So the DC equivalent circuit was easy to draw. My concern is about the final answer. The answer given does not match the answer I've...
45. ### Unknown value of added resistor in parallel

Homework Statement Picture provided. The current going through the resistor R1 in the figure does not change whether the two switches S1 and S2 are both open or both closed. The resistances are R1 = 14.00 Ω, R2 = 142.00 Ω, and R3 = 24.00 Ω. The voltage is V = 11 V. With this information, what...
46. ### General DC Circuit: Voltage drop different from supply source

Homework Statement I performed a lab with a simple DC circuit. The circuit has 4 resistors (i.e. R1, R2, R3 and R4), which is the same as shown in the attached image. When the voltages across all resistors were added, they were higher than the source. How is this possible? The KVL rule states...
47. ### Engineering Circuit to change the current and voltage of a dc circuit?

I wasn't sure whether to post this here or in the 'homework' section... technically it is not a homework question, but I will be happy to move it... I am really struggling with this circuit: :'( At the moment, I have no clue what to do for part i). I am sure that I will get part ii)...
48. ### Engineering Question about dc to ac circuits in solar panels?

Homework Statement It can be shown that a square wave can be represented by a sum of sine waves as given by the formula below v = v0sinωot + v1sinω1t + v2sinω2t + v3sinω3t +... Solar cells have an output that is dc. The pd across a cell depends on the incident radiation and the efficiency of...
49. ### Transforming DC to AC: The Role of Inductors and Capacitors in RLC Circuits

I have only just found out about inductors, and am trying to figure out how a circuit with an inductor and a capacitor could change dc current to ac current. With the set up of the circuit, would it suffice just to have the dc supply with a 'gate' that stops/allows through the dc current with a...
50. ### Power dissipated by a resistor in combined citcuit

Find the power dissipated by R2 given that V a-b=120 volts, R1=1, R2=3.33, R3=2, and R4=3 I've worked this problem, just want to confirm I worked it correctly. A---------R1-----------*------------------- | |...