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Questions tagged [electric-circuits]

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

2
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1answer
55 views

Turning off an inductor: Experimental problems

I am trying to measure the current in dependence of time in turning on and off an inductor. If I choose an inductor with low inductivity (36 mH) it works for turning on (almost) as expected, but for ...
-3
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1answer
64 views

Why does a battery powered radio's volume go down as batteries age, even when the batteries' voltage is constant?

A set of batteries are used for a long period of time. Explain why the volume of a radio is low even though the voltage of the batteries is the same as when they were first bought.
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4answers
60 views

Voltmeters confusion [closed]

Voltmeters must be connected in parallel with the resistor. It must have a very high resistance so that it does not alter the amount of current through the resistor. But what will happen if its ...
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0answers
82 views

Could the tether of a space elevator be used as a single-wire transmission line?

If you're unfamiliar with single-wire transmission lines: https://en.wikipedia.org/wiki/Single-wire_transmission_line It seems that a material with high conductivity (eg: certain configurations of ...
-2
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1answer
48 views

But total power dissipated in the two resistors in 3W. Where has the balance (rest) power 3W gone? [closed]

Question 2: In the network of fig-2 shown in below. If you calculate and then get power supply by the battery 12V 6W. But total power dissipated in the two resistors in 3W. Where has the balance (...
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2answers
113 views

How do we understand L C Oscillations (Inductor - Capacitor Circuit Oscillation) Intuitively?

How do we understand L C Oscillations (Inductor - Capacitor Circuit Oscillation) Intuitively? How to intuitively understand the Phase Lag and Imagine What is happening in the circuit exactly without ...
1
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1answer
53 views

Underground river of lightning?

This question has been asked before but not the same way. A generator uses a magnet to push electrons down a wire to my house and turn on my light. Then those electrons take the expressway back to the ...
1
vote
1answer
148 views

Violation of KVL ,KCL at high Frequencies

question: How can we prove mathematically that KVL (Kirchoff's volatage law) and KCL (Kirchoff current law) become invalid at very large frequencies? i have read this statement in my book but it ...
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3answers
71 views

When talking about potential difference in a circuit, whose work done are we talking about?

I'm asking this because it seems to me that when we talk about PD around a charge (i.e. potential difference between infinity and a point), we're talking about the work done per unit charge by an ...
2
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4answers
97 views

In a simple battery + resistor circuit, what form of energy is lost from the electrons upon exiting the resistor?

I will give this question a little context. Firstly, as I understand it, as soon as I "close the switch" on a circuit, electric current pretty quickly establishes a steady state where, at any given ...
1
vote
1answer
43 views

Electromagnetic thrust force

If I put a wire near solenoid/electromagnet and put DC current in proper direction (Fig 1), then there will be force going up which will pull the wire up. But according to 3rd law of Newton there will ...
1
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1answer
40 views

Question about deriving Resistance from data on Electric Current in Two Different Scenarios

I am preparing for an undergraduate degree in Physics, with no teacher in sight until October. The textbook I am using to prepare myself, gave me the following exercise about electric current and left ...
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2answers
114 views

Why a bird does not get electrocuted when it is sitting on a high tension electric wire? [duplicate]

Why a bird does not get electrocuted when it is sitting on a high tension electric wire?
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2answers
39 views

Does electric current create positive ions while flowing through a conductor?

As the conduction electrons are free to move randomly, i.e they are not restricted to a particular atom, then why don't these atoms get positive charge due to loss of these conduction electrons?
2
votes
1answer
70 views

Thermoelectric voltage over a solder joint of two identic copper wires

My background: I'm engineer of electronic HW engineering and embedded computer systems. During repair of a vintage digital voltmeter (resulution 1µV) I discovered an effect that probably only a ...
1
vote
2answers
25 views

Power factor in Transamision

What is normally the power factor in the transmssion.? Is there some standard or guidelines for that.? Also, the low factor is not desirebale as it leads to more power loss. That makes sense. They ...
0
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0answers
28 views

Connection between wave equation of voltage and refraction coefficients

We have the solution to the wave equation of voltage $$U(x,t)=(U_+e^{-x\nu}+U_-e^{x\nu})e^{i\omega t}$$ But when we calculate the voltage at a particular time, we use the refraction coefficients. ...
0
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4answers
79 views

Why magnet do not feel force?

The magnet is falling downward under the action of gravity. As there is relative motion between electrons and magnet the electrons will feel force ( F= qvB )and according to the Newton's third law ...
6
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1answer
2k views

What is the electrical difference between rolled and unrolled extension cables? [closed]

I am talking about the extension cord of length 10 meter or more as follows. The clerk said that it is better to unroll it when using. So what is the difference? I know for alternating current there ...
-1
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3answers
41 views

Self induced EMF in DC

Why is self induced emf much greater than the source voltage in a DC supply when the switch is opened?
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0answers
18 views

How to calculate the total emf and current in a secondary winding composed of multiple materials

In transformers, flux swings in the primary winding induce an emf in the secondary. Typically the secondary is taken to be a single material, but if it is instead taken to consist of multiple ...
3
votes
3answers
170 views

How can a transformer produce a high voltage and a low current?

I understand that in ideal transformers, power is conserved. Because of this the product of voltage and current in the secondary winding is a constant. This means that voltage and current are ...
4
votes
5answers
125 views

Inductor in A.C. Circuit

I am reading about inductors connected in A.C. Circuits. I understand mathematically that the current lags behind voltage. But what is the physical explanation for this? My understanding: As the emf ...
3
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2answers
41 views

Energy and Speed of Electrons in a Circuit

I really wonder about the relationship between potential and kinetic energy in a circuit. At the positive terminal of the battery, there will be high potential energy. The difference in electric ...
0
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0answers
40 views

Charged particle near a loop of varying current

Consider a loop of radius $R=1$ centered at the origin lies on the $x-y$ plane, carrying an electric current $I$. A point particle of charge $q$ is located initially at $(0,0,z)$ and at rest. The ...
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0answers
29 views

understanding lock-in measurements (XY display mode)

I am trying to understand the lock in measurement performed here. Mainly, I am trying to understand how they were able to choose the phase offset based on the plot (first image below). In the ...
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2answers
36 views

Ideal Capacitor (Introductory Physics Question)

If I have a simple setup of a open circuit with a battery (constant battery) , resistor, and uncharged capacitor, and then I close the switch of circuit, and keep it closed until the capacitor is ...
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2answers
84 views

The rail gun experiment revisited

A metal rod is closing a horizontal electric circuit as shown here. We apply a vertical magnetic induction $B$ as shown. The magnetic (Laplace) force on the rod is $F=I\ell B$ to the right. If $F$ is ...
3
votes
4answers
87 views

What does electrical potential at a point mean?

From my understanding, potential difference (or voltage) between point A and point B is the difference in electrical potential at the two points. The potential difference is also, the work done per ...
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4answers
85 views

Capacitor connected to battery at one end

I was recently solving a problem that involved a circuit with a capacitor that was connected to a battery at one end(the second plate just had a wire which didnt lead anywhere).  In the solutions it ...
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0answers
82 views

On surface charges in simple electric circuits

In several articles / textbooks it is written that when wires / circuit are connected to battery, there is very short transient state during which surface charges will appear on the wires. From A ...
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1answer
61 views

How does energy flow in a circuit?

I read some information on a certain blog saying that energy does not flow inside the wires of a circuit, it propagates in the form of an electromagnetic field outside the wires and straight into the ...
0
votes
1answer
30 views

Wiring a charger to a battery [closed]

I have an AC to DC charger and a battery that have mismatched connectors. I stick my voltmeter in and determine the positive and negative terminals of each. The negative is the one with the black wire ...
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1answer
550 views

Calculation of voltmeter reading [closed]

What will be the voltmeter reading of the circuit?
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2answers
51 views

Conservative $E$-field and Kirchoff rule in practice

In undergrad physics, when analyzing an LR circuit, it is often considered that Kirchoff rule holds. However, as far as I understand, Kirchoff rule only holds when E field is conservative (curl of E ...
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1answer
117 views

Assistance with visualization of alternating current

Sorry, I'm already ashamed to ask for your help. But I'm feel that I needed in some hints about how to imagine alternating current. I really realize I have trouble with it during reading this document ...
1
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1answer
150 views

Magnetic Flux conservation

My teacher said that after switch is shifted (after very long time), $\phi_i = \phi_f$ $\implies i_oL = i3L \implies i = \dfrac{i_o}{3} $ where $i_o$ is $\dfrac{\varepsilon}{R}$ So the initial ...
1
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2answers
77 views

Does potential at a point in circuit allows the flow of charge?

Suppose I have the following circuit with lamp connected and there's also a really long neutral ( total charge zero ) conducting wire under the circuit as follows : Then , from the theory of ...
2
votes
1answer
98 views

Is $\rho=\frac{E}{J}$ a generalisation of $R=\frac{V}{i}$?

Mathematically, by relating the intrinsic quantities like drift velocity,relaxation time etc., it is easy to show that $$\rho=\frac{E}{J}$$ and $$R=\frac{V}{i}$$ are true. But, is it ...
2
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1answer
123 views

Derivation of power equation for electric circuits

I am studying the fundamentals of electric circuits and have been stuck with the proof of the (instantaneous) electric power used in circuit analysis: $$ p \left({t}\right) = v \left({t}\right) i \...
2
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1answer
94 views

How is voltage defined when E changes?

Short version: If voltage is defined for conservative vector field $\vec{E}$ only, at what point in a changing electric field does voltage become undefined? Long Version: Voltage is typically defined ...
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2answers
52 views

Charging current in open AC circuit

I watched the lecture and at this point there is mention about AC generator and wall outlet, that there is only voltage and, obviously, no current until we plug in some load. Since that, one thing ...
0
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1answer
48 views

What actually is the EMF in a current carrying wire?

My basic idea of what a DC current is that, when a potential difference is applied to the ends of wire it creates a force which propagates through the wire all the way to the other end. It propagates ...
0
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2answers
58 views

Resistance of an inductor in direct current

In a multiple choice question a simple circuit of only a battery and an inductor the length of the inductor is doubled. The question is how does the velocity of the electrons change. Big spoiler alert:...
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1answer
100 views

voltage drop of LC filter in reverse

Two questions that are probably really simple to others. If we are to measure the voltage drop across the capacitor, the same way the circuit above is usually used as an LC filter, we would get the ...
6
votes
2answers
99 views

Is there a fundamental reason why “dynamic energy storage” is lossy?

Consider springs and moving masses - both can be used to store energy, the spring via tension $E=\frac{1}{2}kx^2$ and the mass via kinetic energy $E=\frac{1}{2}mv^2$. But day to day experience tells ...
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1answer
44 views

Are EMF and inductor in parallel or in series in a pure inductor circuit

How can we say whether the applied emf and the inductor in the the image are in parallel or in series? In some discussions I have seen people taking the applied emf and inductor to be in parallel and ...
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0answers
24 views

Effect of moving conductor on drift velocity of electrons

The question is a bit trivial, but due to not much familiarity with electromagnetism and all, I would like to have it cleared from you all. I have a current carrying circuit and there is wire which ...
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1answer
17 views

Does power dissipate on real conductor when charge move from charged object to neutral charged object?

for example we have charged sphere and we have neutral charged sphere After we connect them with real conductor (few Ohm resistance) some charge will move from charged sphere to neutral sphere. Will ...
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2answers
46 views

Electron-Current Relationship

I have a rather simple conceptual question that I cannot seem to find a straightforward answer to online. My question is "Does increasing the amount of electrons or increasing the speed of the ...