All Questions
124
questions
0
votes
3
answers
48
views
What happens to the charges in an inductor when you induce a voltage?
Say you have two inductors, and - very much like a transformer - you connect the first one to a voltage source, then place the other one close to it, so that there will be an emf induced by the change ...
0
votes
2
answers
73
views
Cannot catch a minus sign mistake when deriving the ODE for an LC circuit
It's probably a very basic question but I just cannot wrap my mind around it. I'll just try to derive the differential equation for an LC circuit:
According to the law of induction, in a solenoid we ...
- 4,887
0
votes
1
answer
49
views
Voltage drop across an ideal inductor
I was afraid to type the title of the question though there are lot of answers to similar questions. I spent half a day going reading these questions and trying to understand the answers posted and ...
- 65
0
votes
1
answer
92
views
Inductors with different directions connected in series
I know that inductors oppose the change of the current. So for two inductors with different direction in series (one in clockwise and the other in counterclockwise), the equivalent inductor is $L_{eq} ...
- 1
0
votes
0
answers
31
views
Current sensitivity in transformer scheme with SQUID
I've tried to determine the maximum current sensitivity in this transformer scheme but I'm not sure if my solution is valid. I need to find the relation between the current in the input transformer ...
0
votes
3
answers
62
views
Can an inductor increase circuit current?
Suppose there is a simple circuit with a resistor, battery and inductor. The question that came to me is, by opening the circuit breaker, can the inductor be used to oppose and slow down the circuit ...
0
votes
1
answer
47
views
Thought experiment: EM fields and coils
Hello Physics Exchange,
I have been thinking a lot lately about EM fields. I thought about something the other day and wanted to check with the experts if my intuition is correct or not. I know this ...
0
votes
2
answers
68
views
Maximum Impedance for LCR series circuit
Impedance of an LCR series circuit can be maximum when either Inductive Reactance or Capacitive Reactance is maximum at an instant of time.
Max Capacitive Reactance is at minimum frequency, and max ...
0
votes
1
answer
35
views
What does "90 degrees ahead of phase" mean in inductance problems?
I've been working on this homework problem and I have determined that the induced EMF on the right coil is sin(x-90). However, I do not understand what "ahead of phase means." When I graph ...
- 101
0
votes
3
answers
69
views
Are there losses in an ideal transformer?
In a circuit with an AV power source $V$ and a zero-resistance ideal coil, the power from the source. $P_{in} = IV$ is equal to the rate of change in the magnetic energy $U_B$ stored in the coil. The ...
- 2,141
0
votes
0
answers
29
views
Is AC voltage across transformer pi shifted?
Suppose the voltage in the primary coil in a capacitor be
Vprimary = Vosin(wt)
According to my understanding, as the (AC) current in the circuit increases, the Magnetic flux across the secondary ...
- 153
1
vote
2
answers
78
views
Telegraphers' equations for lossy transmission line when $R$, $L$, $G$, and $C$ are frequency dependent
The telegraphers' equations are commonly written as
$$\frac{{\partial v(z,t)}}{{\partial z}} + R\space i(z,t) + L\frac{{\partial i(z,t)}}{{\partial t}} = 0$$
$$\frac{{\partial i(z,t)}}{{\partial z}} + ...
- 11
0
votes
0
answers
26
views
Determining the condcutivity of a material by method of contactless resistance caused by putting a sample rod in the inductor of an RLC circuit
I'm doing an experiment where I'm trying to determine the conductivity of a material by putting a sample rod in the center of a coil which is a part of an RLC circuit with an AC generator.
I was told ...
1
vote
1
answer
221
views
Current and Magnetic Poles of a Solenoid (Diagram) & Right Hand Thumb Rule
Well, my doubt's pretty elementary.
Firstly I wanted to confirm whether both the cases, as illustrated in the picture, are correct. I've darkened the part of each coil that faces us. Using the clock-...
- 72
2
votes
5
answers
109
views
Magnetic field in a capacitor in a $LC$ circuit
Consider a simple $LC$ circuit in which the charge on the capacitor varies sinusoidally. Current flows in this circuit, changing the charge on the capacitor and hence changing the electric field ...
- 29
0
votes
0
answers
52
views
How to find magnetic permeability of a mixed core?
Inserting a ferromagnetic rod into the core of an inductor increases its inductance. If the change in inductance is known, the following equation can be used (or so I assume) to find the relative ...
1
vote
3
answers
458
views
Does the unit "volt-seconds" have any interesting interpretation?
I was contemplating the units of capacitance and inductance in electrical circuit theory and noticed something that bugs me. Although there are many equivalent ways to write the farad (seconds per ohm,...
- 113
0
votes
2
answers
41
views
If we change the direction of the connections in a step-down transformer, will it become a step-up transformer?
If we change the direction of the connections in a step-down transformer, will it become a step-up transformer?
1
vote
1
answer
52
views
How can Current Flow through the Inductor in the AC Circuit? [duplicate]
It's said that if the inductor is connected to the alternating voltage source, alternating current will be created in the circuit. Changing magnetic flux through the inductor will induce a voltage as ...
- 515
0
votes
0
answers
27
views
Why are partial derivatives of Energy and Co-Energy with respect to x opposite numbers?
In a system where the flux linkage $\lambda = \lambda(x, i)$ is a function of dispalcement $x$ and current $i$.
Its energy is defined as
$$
W = \int_{0}^{\lambda} i(\lambda', x)d\lambda'.
$$
Its co-...
2
votes
2
answers
333
views
Inductance of air core inductor with and without load
I have an air core inductor whose inductance , as measured with LCR meter, is 45.1uH and quality factor is 4.4. When i place an Aluminum alloy (which is a Non-magnetic Material) as Load inside the ...
- 21
4
votes
1
answer
63
views
Why In the following $RL$ circuit, the connection to $b$ must actually be made an instant before the connection to $a$ Is broken? [duplicate]
In Resnick halliday, student 10th edition page - 795. In the topic current decay in RL circuit, the following statement is used, the connection to b must actually be made an instant before the ...
- 43
3
votes
1
answer
216
views
What is the electric field around an inductor?
This question comes from this Walter Lewin video at 35:00 where he says "I'm going to confuse you even more" (and I suppose he somewhat succeeded). Walter Lewin claims there is an electric ...
- 8,640
1
vote
0
answers
19
views
Doubt in RL circuit and Kirchoffs law [duplicate]
We know that kirchoff's second law is based on the fact that in any closed circuit: $$\oint \vec{E}\cdot\vec{dl}=0$$
Now let us take a simple LR cirucit with one battery $E$,resistor $R$, inductor $L$....
- 2,042
0
votes
1
answer
111
views
Doubt in the mode of action of inductor in the RL circuit
I feel that my initial question was slightly incoherent and not precise. So instead of making addendum to the question which is making it lengthier, I am editing it completely. So, sorry about that.
...
- 436
3
votes
0
answers
194
views
Wave equation derivation in a transmission line
$$
V(x, t) = L\Delta x\frac{\partial I}{\partial t}(x, t) + \frac{1}{C \Delta x}\int{I_c(x, t) \; dt} \tag{1}
$$
$$
V(x + \Delta x, t) =\frac{1}{C \Delta x} \int {I_c(x, t) \; dt} \tag{2}
$$
$$
I(x) = ...
- 1,525
2
votes
1
answer
123
views
Why is the product of the $L$ and $C$ matrices for coupled transmission lines diagonal?
Background - transmission line
$\newcommand{\ket}[1]{\left \lvert #1 \right \rangle}$
A transmission line can be modeled as an infinite sequence of inductors and capacitors:
...
- 24.6k
2
votes
4
answers
250
views
Inductor connected to an AC source
Consider an inductor connected to an AC source, $V=V_0\sin\omega t$.
Let the the switch in the circuit be closed at $t=0$. Then by Kirchoff's voltage law,
$$
V-L\frac{dI}{dt}=0
$$
where $I$ is the ...
- 23
0
votes
4
answers
200
views
Why $di/dt$ in inductor circuit reduces gradually after closing the switch?
When we close circuit having an inductor, an induced emf is generated across the inductor which opposes change in current through the circuit. This back emf depends on rate of change of current $di/dt$...
1
vote
2
answers
224
views
Doubling the length of a solenoid doubles its inductance. Two identical solenoids in series have up to four times the inductance due to M. Why?
The inductance of a long solenoid with $N_o$ turns and a length $l_o$ is
$$L_o=\pi r^2 \mu_0\frac{N_o^2}{l_o}$$
If I now make a new solenoid, $L_{new}$, with double the length of the original ($l_{new}...
- 1,581
0
votes
1
answer
304
views
Doubt regarding the calculation of EMF due to self-inductance and mutual inductance
When finding the EMF induced in an inductor due to both self-inductance and mutual inductance, the EMFs due to both of these contributions are summed. However, I have doubts regarding their summation.
...
- 65
1
vote
0
answers
31
views
Inductance in case of volume and surface currents [closed]
Is inductance always just defined as the constant relating flux directly to current? Is it true even for surface and volume currents?
- 468
0
votes
2
answers
296
views
Does the EMF induced in an inductor due to mutual inductance equal the total EMF?
For an inductor in a circuit without a power source, does the induced emf found by using the mutual inductance value include self inductance, or is the self induced emf considered separately?
From ...
- 65
1
vote
1
answer
182
views
Are we always allowed to treat an inductor as a battery with the same voltage?
When there is an induced emf, Kirchhoff's Loop Rule no longer is true, because electric fields are nonconservative when there is an induced current, as stated by Faraday's Law:
However, I have seen ...
- 323
0
votes
1
answer
44
views
Induced emf by a single wound coil
I was reading Electromagnetic Induction chapter and a question came on my mind..
If I use a circuit with a battery and a single wound coil,and I pass 2A current through it,when the current will pass ...
0
votes
1
answer
99
views
Work done by battery [closed]
In charging a capacitor to a charge $Q$
Is there an equivalent to this in setting up current through an inductive circuit?
Energy stored in inductor $= 1/2Li^2$
What would be the work done in setting ...
- 3
0
votes
2
answers
73
views
What is the difference between the self-inductance of a branch and self-inductance of a loop in lumped circuit models?
When we talk about lumped circuit model, I get confused about the terminology that is generally used. For a loop, we do know that the total flux through the loop can be written as $\Phi = \Phi_{ext} + ...
- 1,000
1
vote
3
answers
112
views
Inductance in AC circuit
Why does an inductor oppose a change in current and not voltage? Is it a rule or is it because of lenz's law? Because intuitively the back e.m.f which opposes a change in current should also oppose a ...
- 117
4
votes
1
answer
299
views
Why can voltages be summed around a circuit if there is magnetic induction?
So there is this class I'm attending on Electronic Instrumentation which involves mostly circuit analysis. For example, RCL circuits, and circuits that also contain opamps, transistors, diodes, etc. ...
- 117
1
vote
2
answers
515
views
What is the amplitude of current in LC oscillations
Since there is no resistance in an LC circuit (not attached to an AC source), what's stopping the current from rising to infinite. And if resistance is provided by the inductor by self induction, then ...
- 105
2
votes
3
answers
644
views
How is EMF still induced in an incomplete/open circuit?
I understand that current can't flow through a coil if it is not complete, but surely this means that if a magnet is dropped through the coil, no EMF would be induced either, since work is done when a ...
- 31
0
votes
2
answers
431
views
Is the voltage drop across an inductor in a purely inductive circuit equal to $X_L\times I$ or back EMF?
In a purely inductive circuit, due to Kirchoff's voltage law we say that voltage drop across the inductor is equal to (negative of) applied AC voltage. However whenever we calculate the voltage drop ...
- 21
1
vote
0
answers
64
views
Inductance and Mutual inductance
Question: Three coils with inductances $L_1, L_2$ and $L_3$, as well as mutual inductances $M_{12}, M_{13}$ and $M_{23}$ are connected in series. What is the total inductance?
The right answer is $L_1+...
- 13
5
votes
5
answers
2k
views
Where does the energy stored in inductor go on opening the switch?
Suppose we have a simple RL circuit. At $t=0$, I close the switch so that current starts flowing in the circuit. When the steady state is achieved, current $i=\frac{\epsilon}{R}$ would be flowing in ...
- 123
1
vote
2
answers
1k
views
How can we derive the polarity of the induced voltage in an inductor?
As we know, the voltage-current relation of a two-terminal constant-inductance inductor is:
$v_L(t) = L \, \dfrac{\mathrm di_L(t)}{\mathrm dt} \tag 1$
I've managed to prove that equation without ...
- 344
0
votes
1
answer
1k
views
Formula for The Voltage of a Coil
I've seen 2 different formulas being used for the voltage of a coil in a circuit. The first one is $$U_L=L\cdot\dot{I}$$ and the second one is $$U_L=-L\cdot\dot{I}$$ The first formula was used in a ...
- 3
0
votes
1
answer
115
views
Is an increase in inductive current caused due to an increase in magnetic field?
I'm studying Inductive current in high school. I learned the Faraday law, and that the voltage produced is equal to the delta of magnetic field flux over time.
So, I was curious about this topic and ...
- 3
0
votes
0
answers
12
views
How to find the canonical equations of the series RLC circuit? [duplicate]
First, I consider the LC circuit with an ion in the capacitor, which is like this:
The current $I$ can be derived easily using Shockly-Ramo theorem
\begin{equation}
I = -\frac{qp}{dM} + C\dot{U} \ \ ...
- 68
0
votes
0
answers
111
views
How to find the canonical equations of the RLC circuit
First, I consider the LC circuit with an ion in the capacitor, which is like this:
The current $I$ can be derived easily by using Shockly-Ramo theorem
\begin{equation}
I = -\frac{qp}{dM} + C\dot{U} \...
- 68
0
votes
1
answer
585
views
Inductor EMF direction
I have some serious troubles with understanding the EMF in inductor.
Assume we change the current from value $I_0$ to zero by rotating the tumbler of the source.
Then why should we consider the EMF ...
- 258