An electronic system, with closed loop current flow, and relative electrical potentials present across electrical components.

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Thevenin equivalent voltage and resistance of a circuit: verification needed

Here is my reasoning: We have to sources so me must use superposition: We first replace the current source by its resistance which is infinite for an ideal current source. Now we need to measure ...
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3answers
117 views

Definition of equivalent capacitance

I know that equivalent capacitance of multiple capacitors in series is $$ C = \left(\frac{1}{C_1} + \cdots + \frac{1}{C_n}\right)^{-1} $$ and in parallel is $$ C = C_1 + \cdots + C_n. $$ But there are ...
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144 views

Finding the equivalent resistance

I'm having hard times understanding why when you combine 20 and 30 resistances which are in parallel, and then combine 60 and 40 (which are also in parallel) ohms resistances you will get two parallel ...
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1answer
82 views

Circuit with three capacitors

A potential difference of V = 38.0 V is applied across a circuit with capacitances C1 = 4.1 nF, C2 = 4.7 nF, and C3= 2.3 nF, as shown in the figure. What is the magnitude and sign of q3l, the ...
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1answer
46 views

Why is resistance $U/I$ rather than $I/U$?

What is the difference between resistance and conductance and why is resistance $U/I$ and not $I/U$? (I know $I/U$ is conductance.) But I don't see the difference between both.
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41 views

Why do we consider current to be constant throughout a circuit? [duplicate]

Let us consider a circuit made up of connecting wires, a resistor, a switch and a battery. Now, the resistance of the resistor is much higher than that of the wire. Now, intuitively, I am thinking ...
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4answers
165 views

The sign of the current flowing in a circuit

I was doing the following problem: And I was asked to find Iy. I found Iy to be 2.64 using KCL. However, the right answer was negative 2.64. Is it negative only because there is a dependant ...
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1answer
47 views

Why does a variable potential divider have the ability to reduce current through a component to zero

For example, the diagram in my text book: shows a filament lamp, in series with a uniform resistive wire, which can have its voltage and current varied by moving the sliding contact, e.g., a ...
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1answer
92 views

How is a potential divider able to reduce current to zero?

For example, a filament lamp, in series with a uniform resistive wire, can have its voltage varied by moving the sliding contact, e.g., a rotatable wheel. However, why is a potential divider able to ...
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1answer
87 views

Capacitors and external electric fields

I am grading questions from the lab manual provided by the professor to review with the students. I am trying to wrap my head around one of the questions about what an external electric field would ...
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2answers
95 views

What exactly is potential difference? What are the factors that effect it?

I am asking this question because at first I thought that this concept was pretty clear to me, but it is not. So, my first question: Is potential difference only a property of an electric field? If ...
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0answers
16 views

Are diodes (or FETs) electrets?

The explanations I see of diodes and FETs seem to involve various depletion regions, migration of electrons and holes, and the such. My (perhaps naive) interpretation of these explanations implies ...
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2answers
76 views

The separation between the two plates of a capacitor is increased

I had the following question on a quiz recently: A capacitor consisting of two parallel plates, separated by a distance $d$, is connected to a battery of EMF ε. What happens if the separation is ...
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1answer
45 views

$P=V^2/R$ confusion

I am confused on how to apply the formula $P=\frac{V^2}{R}$ If I am given a bulb say with power 60W and it is connected to a supply of 120V. Then the resistance of the bulb is 240$\Omega$ but if ...
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1answer
48 views

Why is Kirchoff's Voltage Rule not satisfied when the circuit is shorted?

For example if I have a simple circuit with a battery and a resistor, and then the resistor is shorted, Kirchoff's Rule is no longer satisfied. Since the current through the resistor is 0, the voltage ...
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2answers
101 views

Why didn't 0.2A at 2V kill me? [closed]

I was recently connecting a circuit together like here: and I had the voltage set at 2V, with a 10Ω resistor. By Ohm's law, there was a current of 0.2A (and was confirmed by my multimeter). I ...
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4answers
6k views

Capacitor Charging and Discharging when connected to the ground

When we charge a capacitor using a battery and then remove the battery, the plates of capacitor becomes charged. One holds positive charge and the other one gets equal negative charge. o. k. ? Now ...
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2answers
63 views

How to find the current source Is and the voltage V1 of this circuit schematic? [closed]

I have Vs= 1.5V, R1=1 Ohm, R2 =6 Ohms, I got the equivalent resistance to be 7 Ohms. Then I set equal Req to Vs for 7I=1.5 and got my current source to be 0.214A. Since it is only Vs and Req in the ...
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7answers
16k views

What is Electromotive force (EMF)? How is it related to potential difference?

What is Electromotive force (EMF)? How is it related to the potential difference? Is it created by the potential difference in any conductor? Is it a process? Why is it called force? Does writing EMF ...
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2answers
58 views

If the electric potential is location dependent, why do charges loose it when passed through a heavy resistor in a circuit?

I really cannot understand this: I know through reading that unlike electric potential energy, which is charge dependent, the electric potential is purely location dependent. For example: If at a ...
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2answers
109 views

If there is a potential difference between the ends of a battery, does it mean that there is always an electric field?

First of all, I am really sorry if this question is wrong. But, I thought that this would be the best place to ask this. Here is what I am thinking: Batteries promote flow of current in a circuit due ...
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0answers
19 views

How to think about Ripple and Noise in circuits

Say you have a AC to DC power supply. If you were to hook an oscilloscope up you would see noise occurring. Some of it would appear to have a regular frequency in Khz or Mhz. Would this put off EM ...
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2answers
34 views

Voltage across voltage source in a short circuit

When we short-circuit a voltage source, the current will be very high. The voltage across the wire is 0V. If we apply KVL, also the voltage across the voltage source is 0V. How can it be 0V if we have ...
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2answers
89 views

Ohm's law experiment

I was going through my physics laboratory manual. In the Ohm's Law Experiment, the book states a few precautions without any reasoning. 1.The wire whose resistance has to be determined should ...
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1answer
165 views

Calculation Equivalent Resistance In A Circuit With resistances connected in a circle [closed]

I am having trouble in finding the equivalent resistance between the terminals 'a' and 'b' in the following circuit: Please can anyone explain to me how to solve such problems. Thank You!
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1answer
130 views

Why does energy flow between a high voltage transmission line and linemen approaching it on a helicopter?

The video High power line workers shows linemen servicing a live high voltage transmission line. As the helicopter approaches the line, the lineman reaches out with a metallic wand that is ...
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1answer
137 views

Why is a series resistor needed in a simple thermistor experiment? [closed]

I have come across the following simple question, however I can't see any need for a fixed resistor in series. The only possible reason that I can think of is that the resistance of the thermistor ...
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0answers
36 views

How to control a dc motor? [closed]

I am in 8th standard and I am doing a project on 3d printing pens. I want to know how to control a dc motor, so that when I press a button it should increase its speed gradually till it reaches its ...
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4answers
120 views

Voltage of a battery in a circuit with an infinite resistance [closed]

I have a dilemma that I would like to share with you concerning batteries (without neglecting internal resistance), emf and resistance of a circuit. To better visualize my question you may need to ...
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1answer
56 views

Help to solve a circuit with capacitor and resistor

Till now I'd never solved a circuit with resistor and capacitor. I'd seen the problem and tried to solve. But now I am in a doubt.The circuit was like that- My attempt-
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1answer
30 views

How do I show for an ideal transformer $M^2=L_1L_2$?

I've been stuck on this problem for about an hour. In an ideal transformer, the same flux passes through all turns of the primary and of the secondary . Show that in this case $M^2=L_1L_2$, where $...
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2answers
25 views

Using resistance

I want to know the purpose of using resistance. Is it used to Reduce the amount of current? Reduce the speed of the electrons in the wires? For the first reason: Why do we just don't use a ...
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0answers
42 views

Determining initial voltage across a capacitor [closed]

This one has got me stumped. I have a graph of voltage vs time and a corresponding power vs time graph. Taking the integral of the power vs time graph gives me the work done on the capacitor. Now the ...
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2answers
1k views

Are capacitors and inductors mirror images of each other?

I'm reading through my E&M textbook (Physics for Scientists and Engineers 3rd edition, Knight) and watching as many lectures on YouTube (Shankar, Pomerantz, Lewin, etc) to prepare for next quarter....
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1answer
43 views

How can power factor be improved by using a capacitor in an LCR circuit?

First of all what is even meant by improving power factor? My book says we can improve power factor by making impedance tend to resistance I.e. Z-》R, and then they say that power factor is improved by ...
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1answer
30 views

Resistance in A.C. circuits

Why do electromagnets offer maximum resistance in A.C. circuits?
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2answers
174 views

How do radio antennas follow electrical rules

Power = current times voltage. However current requires a complete circuit to 'flow'. How can a 1,000 Watt antenna work if the output of the transmitter is connected to a single emitting wire or ...
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1answer
117 views

Resistor Puzzle [closed]

I was going through physics competition problems on http://fykos.org/ when I stumbled across this one: ... The Square The Joker The electric circuit in the image is made from the infinite ...
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1answer
55 views
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89 views

Why is Kirchoff's Current Rule valid?

The fact that Kirchoff's Current Rule is valid means that whatever current flows in flows out. But this will only be valid for a steady current circuit, that is, when there is no accumulation of ...
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0answers
19 views

How to apply kirchoff's laws to motors in DC and AC settings

DC case: is it ok to treat a motor as a variable resistor, with resistance depending on the load? AC case: suppose I have a motor that runs at 120V AC and is rated to X watts, how can I determine how ...
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2answers
64 views

Sign of induced EMF and other elements in AC circuit

I am having problems to determine the direction of the induced EMF in AC circuits. For example, we have an inductor of inductance $L$. The induced EMF is given by: $$ \epsilon = - L \frac{di}{dt} $$ ...
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2answers
122 views

Some questions related to circuits and flow of electrons

I have some doubts related to electric fields and flow of current. So, let us assume an electric circuit, which contains a battery and a wire connecting positive and negative terminal of the battery. ...
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29 views

Electric circuit for nonlinear pendulum?

Is it possible to make an electric circuit analogue of nonlinear pendulum? To model the equation $y''=sin(y) $. They did this on analog computers in the past, how? How to model sine-nonlinearity?
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103 views

Input Resistance vs Output Resistance

I am having trouble understanding the difference between these two concepts. I know that input resistance is the resistance as seen by the input terminals and output is as seen at the output terminals....
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0answers
20 views

How do electrons choose their way through nodes? [duplicate]

Suppose I have a circuit, powered by some emf ($V$). If I put two resistors $R1$ and $R2$ of different resistances in parallel, the current at the node is divided following Kirchhoff's circuit laws. ...
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1answer
2k views

Drift velocity of electrons with changing area

What would happen with the drift velocity of a cylindrical resistor's diameter increases, with a given voltage between its terminals? According to the expression: \begin{align} R&=\rho\frac{L}{A}\...
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2answers
79 views

Kirchoff's law, can it tell me the direction of current in this case?

Say I want to find the current Ia in the circuit below: If I use the approach of using kirchoff's voltage law and ohm's law on the left loop, I get $-24V -12k\Omega*1mA -21k\Omega*I_a = 0$ $I_a = -...
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1answer
80 views

What is the condition for resistance in the branch to be parallel [closed]

What if the incoming current at one node not equal to the other, does the resistance in branch still parallel. Eg: In the above circuit diagram how is 17.5 Ω resistor parallel with 5Ω and 2.5Ω ...