Questions tagged [electric-circuits]

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

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3answers
39 views

Why does a voltmeter have to have nearly no current passing through it?

I understand that a high resistance of a voltmeter will allow nearly no current to pass through it. However, why is this condition required? Let's consider a simple circuit that consists of a cell, ...
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2answers
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Why does the voltage drop across the resistor not cause a back current?

Assume a resistor in series with a battery, it can be seen that the voltage drop across resistor is same as across the battery. What I do not understand is why this potential difference across ...
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1answer
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In a fixed voltage case, why does inserting a dielectric increase the energy by a factor of $K$?

When inserting a dielectric, the electric field will do a positive work, and it will lose energy to attract the dielectric. by comparison, when dielectric is inserted in a charge-constant case, this ...
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0answers
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What is equation output voltage in oscillator? [migrated]

I was reading about oscillator circuits but could not find any equation of output voltage in terms of circuit parameters (like mutual inductance, inductance, capacitance, DC sources etc)over internet. ...
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1answer
46 views

Phase Difference in mutual coupling

I was reading about oscillator circuit then in my textbook it was written that we get phase change of π at mutual coupling.But, when I workout through mathematics of situation (which I have shown ...
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0answers
44 views

Conceptual question on Temperature distribution in a rod [closed]

Question is taken from Pathfinder: physics for olympiads. My attempt: As current will be same throughout and we know $$dq/dt= KAdT/dl\tag{1}$$ hence if we consider a small $dl$ element it's ...
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0answers
51 views

Energy associated with capacitor [closed]

Question is in the image taken from "Pathfinder: physics for olympiads". My attempt: initial energy would be 1/2*kcv². As there will be charge kcv for final additional charge cv will be added.so final ...
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0answers
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Voltage amplifier transistor [closed]

Can we make a voltage amplifier by a simple transistor circuit? The voltage gain of this voltage amplifier wil depend on the resistance we put between the Vout- and the Vout+ terminal . And the ...
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1answer
46 views

Application of Kirchhoff's rule [closed]

I came across a problem, in which I was supposed to find the power through the 10-ohm resistor, the one at the top (I forgot to label it). I applied Kirchhoff's loop rule and found the current flowing ...
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4answers
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Voltage as work in electric field and in Ohm's law

I am struggling to reconcile the definition of voltage as work done moving a unit of electric charge between two points in an electric field and voltage in Ohm's law. In the work definition, ...
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1answer
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How can I derive the general expression for AC bridge balance?

For example in Maxwell's bridge, or any AC circuit bridge, we just balance the impedances like resistances in DC Wheatstone bridge. How can I derive the general expression below? Z1/Z2=Z3/Z4 For ...
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2answers
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Conceptual question about capacitors in DC circuits

After a long time when the circuit above has reached steady state and the capacitor can therefore be treated as an open circuit, the voltage at the node directly above the 20 ohm resistor is found by ...
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11answers
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Birds on a wire (again) - how is it that birds feel no current? They are just making a parallel circuit, no?

I have been thinking about this and I know that other people have answered this on here, but there's one part that still baffles me, and it has to do with parallel circuits. If I connect a battery ...
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3answers
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I'm worried about current in an inductor at $t=0$ when it is connected with a DC source

When I connect a dc battery to an ideal pure inductor i think the voltage across inductor should be infinity. Because the rate of change of current should be infinity.because in no time say in $0$ ...
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3answers
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Do resistors heat up with left-over amps?

Apologies in advance if I misunderstand and for my bad explanation. I have heard that resistors heat up when there are left over amps that are not being used. If this is the case, why do most home ...
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Is a 3-terminal magnetic tunnel junction possible?

I am wondering, whether a 3 terminals magnetic tunnel junction can be implemented, as shown in the figure below. At the bottom I have a normal metal (NM), on the top - a magnetic junction (FM = ...
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1answer
850 views

Reduction of Maxwell's equations to classical circuit theory

Can classical circuit theory based on lumped element models be obtained from Maxwell's equations as a limiting case in an appropriate sense? If this is the case, what exactly are all the assumptions ...
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2answers
31 views

Inductor with ac supply

When an ac source is connected with an inductor we have a continuous change in voltage and current across the inductor. According to farady and lenz law we will get an equal and opposite voltage ...
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0answers
20 views

Resonant and non-resonant terms in $RLC$ cirquit

I have tried to solve a differentials equations of a RLC circuit. In the the solution I have terms proportional to $e^{iw_0t}$ and $e^{-iw_0t}$, where $w_0= \sqrt{1/LC}$. The author proposes in the ...
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3answers
38 views

Phase difference between source voltage and inductor voltage

What will be the phase difference between the source voltage and the inductor voltage? Will the two voltages be in phase or will be out of phase. How much out of phase they will be? Note that there ...
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1answer
19 views

Does inductance depend on a bias field?

Considering that the energy $U$ stored in a magnetic field $B$ is scales as $U \propto B^2$. It is clear that if we have two identical coils (same number of turns, area and length), but with opposing ...
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3answers
62 views

How is energy really dissipated in an electric circuit?

I've heard that in a circuit, energy is provided to separate components (lamps, motors, etc.) because of the flow of electrons. How is this possible? Since energy cannot be created, where is this ...
2
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2answers
69 views

How does a current cause a voltage?

In most textbooks I've read, the explanation of Ohm's Law begins by assuming that there is an external voltage applied to a resistive (Ohmic) device. From there, it is explained that this voltage ...
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1answer
42 views

Closed Loops inside a Circuit and Kirchhoff's Laws [duplicate]

Good afternoon! I'm currently taking a physics course, and we're covering Kirchoff's Laws. To the best of my knowledge, Kirchoff's voltage law reads "The sum of the potential differences across all ...
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1answer
20 views

Reverse biased semiconductor diode: Name of the current due to which the depletion layer is getting widened?

I know, that in a reversed biased connection the reverse saturation current flowing is negligible but before the depletion layer is widened to its maximum capacity. It seems the current flowing ...
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1answer
25 views

Is there voltage drops across series resistors with a parallel resistor system?

I am not looking for calculations, I can do that. Please forgive the drawing, my picture wont upload. However, (R1 and R2) are in series. Likewise, (R3 and R4) are also in series. I could not show the ...
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Can someone help me decipher the code for the arduino? I am totally lost [migrated]

The code is as follows: void loop(){ light = analogRead(5); Serial.println(light); analogWrite(3,light/4); }
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3answers
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Confusion about cells in parallel

I cant understand why cells in parallel will last longer. Could someone please explain?
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2answers
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How do you calculate energy losses in an energy grid?

Let's say you have an energy transmission line, that gets powered by an energy plant with a power of 6150MW. You know the line is for example 133 km long and you know the voltage of the power line is ...
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0answers
47 views

Find the current in the 23 ohm resistor using Thevenin's theorem [closed]

How should one proceed to find Thevenin's Voltage across the 23 ohm resistor?
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Studying Chaos in RLD circuit

We are currently working on non-linear dynamics (chaos theory) by analysing a series circuit including a diode (the 1N4004), a 100 ohm resistor and a 20 mH inductance. It is driven by an alternative ...
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3answers
49 views

Current and voltage - Incompatibility between Ohm's Law and Power Law! [duplicate]

Ohm's Law: I $=\frac{V}{R}$: Increasing voltage increases current. Power Law: P $={V}*{I}$: Increasing voltage decreases current. Am I missing something?
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2answers
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Current in a potential divider [closed]

I dont understand why the current in R wont be the same as that in the 50 ohms resistor. Isnt that the rule for series circuits? The emf for the battery is 18 volts.
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What is $C_\mathrm{eq}$ for this circuit? [duplicate]

What is $C_\mathrm{eq}$ for this circuit? I don't even know how to approach such a problem.
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3answers
50 views

Can a resonance plot be upside down, i.e., inverted?

Given the following RLC circuit with an AC driving source, $\hskip3in$ I have found an expression for the amplitude to be $$ I(t) = \left(\frac{V_{0}}{R}\right)\frac{(\omega \tau)}{\sqrt{(\omega\...
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0answers
21 views

How to calculate the battery drain from a LED light knowing it uses 1.5 Ah/month?

My knowledge of physics is basically zero, so I hope this question can be considered on-topic! This thingy connects to the battery of a vehicle (car, motorcycle, scooter etc) and shows the level of ...
0
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3answers
51 views

Would there be a potential difference across a cell connected with just a wire in complete circuit?

My textbook says, that across a battery or a cell there should be a potential drop equal to its e.m.f. Now consider a simple circuit with a cell of e.m.f 9 V. Let us assume a point on the negative ...
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0answers
18 views

How do I find the equivalent capacitance of this circuit? [duplicate]

I am trying to solve the given problem, which asks to find the equivalent capacitance for this circuit. Everything is given in the diagram. How would I go about solving this? I understand that at the ...
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0answers
13 views

DC circuits in the context of a Wheatstone Bridge

What is meant by the output voltage now has no DC component (is zero-mean) in the context of a Wheatstone bridge?
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0answers
12 views

Light illumination variation

If the LDR changes from its original value R0 to R0 + ∆R due to the light illumination variation, what will the relationship between the sensor output voltage and the LDR resistance change ∆R
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2answers
75 views

Why does charge on a capacitor remain constant when dielectric is fully inserted between the plates of the capacitor?

We have a capacitor let's say of capacitance C and is charged by Voltage say V. Then the voltage is disconnected and a dielectric of dielectric constant say k is inserted fully between the plates of ...
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1answer
39 views

What is the microscopic explanation for why is there more power in a circuit with a smaller resistance?

According to the Drude Model of electron flow in a circuit, the drift velocity is inversely proportional to the resistivity. $$E=\rho J$$ $$E=\rho Nev_d$$ $$E=\frac{-\rho Ne^2E}{m}\tau $$ $$\rho=\...
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4answers
86 views

Where does energy go in joining capacitors of different capacitance charged by different potential, hypothetically assuming no resistance in circuits?

I don't understand why there is any change in initial and final energy since we have already assumed a perfectly conductive circuit. I mean, theoretically at least, there should be no change in energy....
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1answer
97 views

Why do I get a short circuit if I connect the red wire? [closed]

Why the red wire generete a short-circuited with $I_2=0$ and $\Delta V_2=0$? I have three loops and if I apply the 2nd Kirchhoff's rule, I will have $$\sum_{\color{red}{\text{2nd loop}}} \Delta V=0$...
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4answers
135 views

Do electrons deccelerate through a resistor?

In a circle the voltage drops across a resistor. This means that some electrons lost some of their electrostatic potential energy. Where does that energy go, and how? For potential energy to be lost ...
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2answers
250 views

Why do the charges on a parallel plate capacitor lie only on the inner surface?

In most pictures I've seen of parallel plate capacitors, charges are drawn so that they're entirely on the inner surface of the plates. I accept that there can't be any net charge within the ...
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1answer
50 views

Does fire caught by appliances causes short circuit [closed]

I know that short-circuit causes appliances to catch fire.But in my exam question was does the assertion is true I think although each of wire has insulation but they are separated by a distance at ...
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1answer
65 views

Relation between $V = RI$ and Ohm's law

According to the book Halliday et al., the equation$V = RI$ is not the Ohm's law but simply the resistance definition; the book states this definition applies to all kinds of conductors, ohmic or not. ...
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0answers
17 views

Large Equivalent series resistance for polarized capacitor

Consider a standard RC circuit with a $100 k\Omega$ resistor and a capacitor. Here's some issue encountered during the lab. When using specifically a polarized capacitor($20 \mu F$), in addition of ...
0
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1answer
36 views

Energy stored in a capacitor vs Work that the battery does [duplicate]

Say we have a battery at a fixed voltage of $V$ charging a capacitor with capacitance $C$. When the capacitor is fully charged, the energy stored in it will be $\frac{1}{2}QV$, where $V$ is the final ...

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