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29 views

Inductor - cause and effect [on hold]

The voltage on an inductor due to alternating current, also called back emf, is given by a beautiful, simple equation. It's just L times time derivative of current. According to Kirchoff voltage law, ...
4
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1answer
32 views

Mutual capacitance upper limit

I am having trouble making an analog for mutual capacitance from mutual inductance. In circuits with magnetic coupling, there is an upper limit established on mutual inductance due to energy ...
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0answers
18 views

Approximate of self-inductance of a square wire coil

Imagine you have a square coil of wires with n turns. In order to calculate the self-inductance coefficient I should know the magnetic field. Is it acceptable to consider the 4 sides as infinitely ...
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0answers
25 views

EMF and Distance

As a professional underground service locator, EMF and Inductance are at the very core of what we do. Very few of us truly understand the detailed physics behind what makes it possible for us to ...
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1answer
33 views

Coaxial waveguide - wave impedance

Determine the capacity $C$ per $m$, the inductance $L$ per m and the wave impedance $Z_0$ for a coaxial waveguide with inner radius $a$ and outer radius $b$. How large would $b$ have to be so ...
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1answer
49 views

Highly inductive circuits question in general

I've been reading about self-inductance in circuits in M. Purcell's Electricity and Magnetism and came across an interesting fact: "What happens if we open the switch after the current $I0$ has been ...
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3answers
32 views

Why do inductors maintain the exact same current?

As we know, a capacitor will maintain the same voltage across its poles even if it is disconnected from a battery source. For example, in this problem: http://www.unm.edu/~toolson/rc_circuit.gif ...
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0answers
33 views

Maximum current in LC Circuits

Two capacitors of capacitance $C$ and $3C$ are charged to potential difference $V_o$ and $2V_o$ respectively and connected to an inductor, all three in series. Now the switch S is closed. Find the ...
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1answer
20 views

Induced current in a loop due to varying flux

Suppose you have a loop of wire beside a infinite long wire carrying a current I. The current in the infinite wire is given by: $$I(t) = I_0(1-e^{(-\alpha t)})$$ Where $\alpha$ is a constant and $I_0$ ...
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1answer
47 views

Does an Inductor maintain it's energy?

Consider a simple LCR ac circuit; generally I (might) understand that the charge exchange between capacitor and inductor would induce a harmonic current flow, but I remain confused for two reasons: ...
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0answers
10 views

Image charges for currents?

I am struggling to get my head around a problem involving creating a transmission line using a wire of radius $a$ in a vacuum a distance $d$ above an infinite grounded plate ($d \gg a$). I wish to ...
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2answers
51 views

Why does electrical impedance have as many parameters as it has?

The impedance of a circuit is written: $$ Z(R,L,C,f) = R + j ( 2 \pi f L - \frac{1}{2 \pi f C} ). $$ What is the line of thinking that frequency, resistance, capacitance, and inductance are the only ...
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0answers
30 views

Mutual inductance versus self inductance of two parallel thin-film wires

I am considering the scenario of two long superconducting thin-film wires (thickness << width << length) running parallel to eachother. They carry a current density that is as usual peaked ...
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2answers
105 views

If induced voltage (back-emf) is equal and opposite to applied voltage, what drives the current?

Suppose we have a circuit with a voltage source, a switch open and an inductor all in series. If we close the switch, the potential difference of the voltage source is instantaneously applied to the ...
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1answer
55 views

Why does the inductance of a coaxial cable not depend on the number $N$ of coils?

Suppose we have a long coaxial cable like in the following figure: I want to compute the self-inductance $L$ of the cable. As I understand, given a coil with $N$ closely winded turns, through which ...
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1answer
19 views

Inductor in transformer

In an inductor, a current waveform 90 degrees out of phase with the voltage waveform creates a condition where power is alternately absorbed and returned to the circuit by the inductor. If the ...
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0answers
39 views

Internal inductance of the outer conductor of a coaxial cable

Suppose there is a coaxial cable with the inner conductor in $ r < a$, vacuum in $ a<r<b$, and the outer conductor in $b < r < c$, what is the internal inductance of the outer ...
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1answer
30 views

Calculating potential difference for fraction of loop with induced current

Given a circular wire loop of radius r, resistance R enclosing a magnetic field perpendicular to the plane of the loop that increases with time ($B=\alpha t$), I have calculated the induced current ...
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1answer
26 views

Circuit with inductor

How would I find the current through each resistor/inductor as a function of time? I am lost conceptually here. (I made these numbers up, so they may not be "pretty" if/when taking equivalent ...
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1answer
42 views

self inductance basic example: meaning of current flow AFTER opening circuit

while studying self-inductiance, I got into a tricky point... Consider this video: https://www.youtube.com/watch?v=0IVJaXO_0XA (minute 13.00). At this moment, opening of the R-L circuit is ...
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1answer
63 views

what is the capacitance and inductance of an ideal wire?

I am reading a magazine for acoustics, one article is about the choice of speaker wire. The article said the ideal speaker wire should has no resistance, capacitance and inductance. I understand that ...
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2answers
32 views

Is it possible for an inductor to have a voltage across it without any current passing through it?

When we calculate open circuit voltages for a non ideal transformer . We have current I2 in the right side loop =0 hence the current passing through L3 must be zero but as visible there exists an ...
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1answer
37 views

Arcing through an inductor

When a current is passed through an inductor coil, potential difference across it is given as $$V=L\frac{dI}{dt} \, .$$ Now, if we suddenly disconnect the coil from the circuit, the current will ...
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0answers
49 views

The affect of high frequency and high voltage AC on induction

I am designing an induction system to wirelessly transfer power a short distance. I was planning on using resonant inductive coupling to increase the efficiency. The Inductance of my coil is about ...
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1answer
54 views

Finding the current and voltage in a circuit with DC sources

I know that in a circuit with DC sources a capacitor(steady state) can be replaced with an open circuit and an inductor(steady state) can be replaced with a short circuit. My understanding is that ...
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1answer
38 views

What does an induced emf do to a loop of varying current?

I know that the magnetic flux through a loop in space is proportional to the current such that $\Phi=LI$. Therefore a change in magnetic flux will produce an emf, so $\mathscr{E}=-L\dfrac{dI}{dt}$. ...
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2answers
102 views

Why can't mutual inductance create perpetual electricity?

Consider the following image. When the battery is connected then current starts flowing through the primary cicuit and magnetic flux changes through the coil, this causes electricity to be induced ...
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1answer
66 views

How can we define the energy stored in a (conservative) force field?

I have come to know from my textbook that energy is stored in the E-field of a capacitor, in the B-field of an inductor and so on. Take the example of an inductor. The derivation bewilders me ...
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1answer
58 views

Confusion regarding inductors

I understand that a change in flux linkages of an inductor results in induced emf across it, the magnitude and direction of which can be determined by Faraday's and Lenz's laws. The magnitude of this ...
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0answers
49 views

Induction in a coil of a hollow conductor

Will a mutually induced AC current in a coil of a solid conductor behave differently from that induced in a coil made from a hollow conductor. Background: A colleague and I are researching for an ...
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1answer
77 views

Why is there current in LC Circuits?

When we connect two electric sources (positive to positive and negative to negative) then the current that runs the circuit is calculated as follows: $ I = (E1-E2)/(2r + R) $ In case of an LC ...
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0answers
72 views

Mutual inductance theoretically decreasing while EMF is increasing in 2 square coil system

I have a quick question regarding electricity and magnetism. I am measuring the induced emf in a square coil of wire with an inductance of 439uH (the other coil is also 439uH and is the same shape). I ...
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1answer
197 views

Transformers - Why more coils in second coil causes more voltage [duplicate]

I am learning about magnetic induction and transformers. I have coil1 which uses AC to create an oscillating magnetic field. I have ...
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1answer
185 views

Constant current in inductor

When I brought the dc voltage from $25 V$ to $0 V$ . A constant flow of electrons I could see in the inductor. Why is this phenomenon happening ? When a constant voltage was supplied the inductor ...
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2answers
460 views

Self induction in transformer

Wont self induction ruin the working of a transformer ? While increasing voltage (AC) in the primary coil, wont there happen a self induction in the primary coil itself ? $E_0 = -L \frac{dI}{dt} $ ...
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1answer
40 views

Can two transformers used to make tesla coils?

Tesla coils seem to perform the same as a transformers: they use two coils and use magnetic field to transfer the energy. Doesn't using two transformers produce the same result? It doesn't seem to be ...
0
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1answer
137 views

Did the derivation of self inductance equation overcalculate winding number? [duplicate]

Let $L , I , \phi$ are self inductance , current and magnetic flux (created by each loop) of a solenoid with $n$ turns . $r$ is the radius of those loops . We have , $LI=n \phi = nAB $ [$A=\pi r^2$] ...
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2answers
489 views

Why do old transformers make sounds, but new ones don't?

What I think is that maybe insulation is gradually removed between plates, and eddy currents start passing from one plate to another and this produces sound. Am I right?
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1answer
38 views

How to model the impedance of a coil with a dielectric slab on the top

I have sketched what I meant in the image below. Were there no dielectric slab, the coil could have been simply modeled as an inductor. But I am not sure what the impedance can be if there is a ...
0
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3answers
620 views

RL vs RC circuits

I find it difficult to understand as to why current behaves differently in an RL and an RC circuit. At time $t=0$, in an RC circuit the current is maximum, whereas in an RL circuit its $0$. Why is it ...
1
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1answer
54 views

Explain why the frequency cutoff for RL circuits is given by $\frac{R}{2\pi L}$

I am studying low and high pass RL filters for Navy schooling. I need someone explain why the frequency cutoff is $fco = \frac{R}{2\pi L}$ mathematically. From my oscilloscope lab results I got the ...
0
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1answer
65 views

Questions about the formula used to determine inductive reactance and $Z_t$

I am currently on the inductors unit in my Navy schooling and I have two questions about these formulas that I learned about. As I'm aware, the ability of an inductor to concentrate a magnetic field ...
3
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2answers
250 views

What is zero impedance in AC circuit?

If a capacitor is connected with an inductor, then because $$Z=\frac{1}{j\omega C}+j\omega L,$$ the Z may be zero. Does that mean when I apply a voltage, the current will be infinite large? What's ...
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4answers
117 views

Current in purely LR DC circuit at t=0

I was told by my professor that the current in a purely LR Circuit with at initial state (JUST after closing the switch) is zero. Can you please help me understand why it that so?
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1answer
26 views

Why does the power in an inductor equal what it does?

I understand that power is that rate at which work is done and that because of this the power in an inductor is equal to $$P=\frac{d}{dt} \left(\frac12Li^2\right).$$ I also understand that the power ...
0
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1answer
55 views

Self inductance & time constant formula

Is this a correct formula for calculating the induced EMF of a wire after the current stabilizes/ or while it stabilizes in the beginning of a DC circuit? What is the difference between the above ...
0
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1answer
221 views

Why do we always consider the area of inner solenoid while calculating the mutual inductance of two coaxial solenoids?

While we know that flux linked to an area is the dot product of the area vector of the loop(and not the actual area encountering the field lines) and the magnetic field linked to it, why then do we ...
0
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1answer
87 views

EMF due to self-inductance? [closed]

I'm trying to calculate the induced $-V$ in a DC circuit when current starts to flow, and reaches it's maximum value. The inductance of the conductor is 1000nH it carries large amounts of current ...
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2answers
360 views

Is there inductance to a DC circuit?

When a DC circuit is carrying current, large amounts or small, is there induced-emf due to the inductance? Or is it only applied to AC circuits?
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2answers
130 views

Electromagnetic Inductance: Different voltmeter readings from different positions

In the setup below, the voltmeter on the right would read differently than the voltmeter on the left even though they are both connected to point D and point A. This picture is taken from Lecture ...