1
vote
1answer
64 views

How can current be a smooth curve?

The following is a graph of the current across some circuit element: Note how the current is treated like a smooth continuous function. Even in the analysis of things (i.e. analysis of the ...
2
votes
1answer
41 views

Sign convention for EMF

When we define the field generate by EMF, why there is not negative sign in $\mathcal{E} = \oint \vec{E} \cdot d\vec{l}$? Usually we talk about potential, there should be a negative sign, right?
1
vote
1answer
86 views

Batteries and fields?

Batteries generate fields in wires that essentially cause the movement of electrons. I think of batteries as two charged plates that essentially contain a mechanism between them to move electrons from ...
0
votes
1answer
16 views

Back EMF & Current, how can we make I stable?

Lets assume we have a wire that has $10V$ across and $1$ $Amp$ flowing, now if this conductor is introduced to a changing magnetic field, $-EMF$ is induced, can we control our voltage to increase it ...
0
votes
0answers
24 views

Does back emf occur in transformers?

Does back emf occur in transformers and if so does it reduce the efficiency of the transformer and can it be reduced?
1
vote
1answer
49 views

Current through two inductors after a long time

I'm having trouble with visualizing the following problem, which is asking me for the final, steady current in both inductors $L_{1}$ and $L_{2}$. I was thinking that after a long time, essentially ...
1
vote
1answer
138 views

How does current flow perpendicular to the wire?

This answer gives a great explanation of how surface charge builds up to force the current to move perpendicular to the wire: http://physics.stackexchange.com/a/102936/41086 However, it fails to ...
1
vote
3answers
145 views

Why do both plates of a capacitor have the same charge?

How do we know that both plates of a capacitor have the same charge? You could argue conservation of charge, but I don't see how conservation of charge implies the charge on both plates is the same. ...
4
votes
1answer
246 views

Why doesn't the electric field inside a wire in a circuit fall off with distance from the battery?

We studied electric fields due to point charges. The magnitude of these fields decreases with the square of the distance from the point charge. It seems to me that we could treat the positive ...
6
votes
4answers
433 views

What is the current of a capacitor when the derivative of voltage is undefined?

This is from the textbook I am reading: I know this equation for capacitors: $$i=C\cdot \frac { dv }{ dt }$$ Here is my question: how can diagram (a) be allowed if the derivative of the voltage ...
1
vote
1answer
107 views

How can electrons move along the conductive wire? ( seems to be a paradox )

Tangential components of the electric field across an interface between two media, with no impressed magnetic current densities along the boundary of the interface, are continuous. So: $ n \times (E_2 ...
4
votes
1answer
441 views

How can KVL & KCL be derived from Maxwell equations?

How can KVL (Kirchhoff's Voltage Law) & KCL (Kirchhoff's Current law) be derived from Maxwell equations in lumped circuits?(Lumped network : if $d$is the largest dimension of the network and ...
5
votes
4answers
182 views

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

What is Electromotive force (EMF)? How is it related to potential difference? Is it the creation of potential difference in any conductor??Is it a process?Why is it called force?
1
vote
1answer
41 views

Energy in a Solenoid?

Consider a circuit consisting of a battery, a resistor and a solenoid inductor. Then, the emf $\mathcal{E}$, is defined as: $$\mathcal{E} = L\frac{di}{dt} + iR$$ Multiplying both sides by ...
0
votes
0answers
43 views

Kirchoff Loop and current

The pic of the circuit/problem: I got the problem right, but i want to make sure my reasoning is correct for the current left of the 2.1 V battery. Its the same current as $I_1$ because the ...
1
vote
0answers
39 views

Different phase in capacitively coupled RLC circuits

I was trying to work with some data for a lab report I'm writing about capacitively coupled RLC circuits. The setup is pretty simple and looks like that: Where $C^{'}$ is the coupling capacitance. ...
0
votes
1answer
57 views

Understanding Counter - EMF?

When an coil rotor is moving around a magnetic field there is -V induced to resist the input V. Let's take an example, a 12 V DC motor induces -10V, and the actual running voltage is 2V. If there ...
0
votes
2answers
87 views

Conversion of Moving coil galvanometer to ammeter

A galvanometer can be converted into an ammeter by connecting a low resistance (called shunt resistance) in parallel to the galvanometer. Firstly, why do we need to connect the resistance? If a ...
3
votes
2answers
309 views

Capacitors: why is the energy not stored in a magnetic field?

When a capacitor is charging, the rate of change $dE/dt$ of the electric field between the plates is non-zero, and from the Maxwell-Ampère equation this causes a circulating magnetic field. Now, ...
3
votes
0answers
27 views

Are magnetic hysteresis losses relevant to alternating currents flowing in a wire?

Say we have an AC in a magnetically lossy material, like iron. Because of iron's relatively high permeability, skin effect will be more pronounced than it is in say, copper, so this iron wire isn't so ...
1
vote
2answers
177 views

Surface charge in a wire?

The image above shows the distribution of the surface charge in a current carrying wire. The surface charges distributes themselves to make sure the field inside the wire is always perpendicular to ...
3
votes
1answer
268 views

Electric field in a wire?

The electric field in a wire is parallel to the wire's surface (it is always pointing "to the front"). If the electric field did not point in this direction, surface charges would build up and ...
3
votes
1answer
71 views

Voltage in a circuit?

The voltage of the battery signifies the difference in voltage between the positive and negative terminal What does this mean? The definition of voltage difference I'm familiar with is the ...
4
votes
3answers
194 views

Reducing Eddy current losses

Eddy currents are setup in any metallic block which is in the vicinity of changing magnetic fluxes. These primarily cause heat losses, and in certain cases causes damping of the relative motion ...
2
votes
2answers
147 views

Does AC current produce EM waves?

Does AC current in simple wires produce electromagnetic waves? AC current entails very rapid changes in polarity and therefore the electrons in the metal will feel rapidly changing forces which should ...
1
vote
0answers
101 views

How does the tester screwdriver work? [closed]

How does the tester screwdriver work? If I put the tester screwdriver inside a "phase" hole of an electric socket, it lits up. If I press my finger against the metal cap on top of the screwdriver. ...
0
votes
0answers
85 views

Microscopic model of RLC circuit equation by analogy to continuous medium mechanics

According to the analogy of mechanics and electricity, the 1-D system of damped oscillation is similar to the RLC circuit. The equation of damped oscillation is $$ f=m\frac{dv}{dt}+\gamma v+kx$$ ...
1
vote
1answer
106 views

Traditional Kirchoff voltage law in AC circuit?

The traditional (not taking into account phasor addition or complex addition) application of Kirchoff Voltage law, i.e. $\Sigma\Delta V=0$ along a loop, does not work for AC circuits. We can sum the ...
0
votes
4answers
155 views

Is voltage important when creating a magnetic field?

Would a DC circuit that has a high current and low voltage have a powerful magnetic field? I'm trying to create a powerful solenoid. In order to create a powerful magnetic field, I'm focusing more on ...
2
votes
2answers
64 views

What is the area in Faraday's law if we have only a piece of metal moving in a magnetic field?

If a piece of metal of length $l$ is moving with a speed $v$ in a region where there is a uniform magnetic field $B$ perpendicular to it, there will be a potential difference across its terminals ...
0
votes
1answer
115 views

Magnetic core, and a DC solenoid

A DC solenoid creates a magnetic field B. A highly permeability magnetic core is added to solenoid to increase B. Now, there is change in flux, due to the increase in magnetic field. What would be ...
3
votes
2answers
111 views

Is there a differential equation that can represent a circuit with an arbitrary voltage source connected acrorss an antenna?

An RLC circuit with a voltage source can be characterized by the differential equation: $$ LC\;\ddot{I}\left(t\right) + RC\; \dot{I}\left(t\right) + I\left(t\right)-C \;\dot{V}\left(t\right) = 0 $$ ...
0
votes
1answer
118 views

Voltmeter Question [closed]

I understand that a voltmeter is used for measuring potential electrical difference, but how exactly should said voltmeter be connected with the resistor in circuit?
-1
votes
2answers
85 views

Time difference in transmission of AC and DC

Is there any time difference while considering the transmission of AC and DC ? Is either one of them faster than the other one in terms of transmission of energy/power from one point to another? I ...
1
vote
1answer
167 views

How to imagine the first few moments of an LR circuit?

For example, there's a very simple circuit which only contains on resistor. So according to Ohm's law, we have: $\mathrm{emf} = IR$ As we know when time $t = 0$, the current must be $I = 0$. However, ...
1
vote
2answers
786 views

how does an electric field comes inside a conducting wire inside the circuit? [duplicate]

This has been a really great confusion for me now .... Many places i have read in books that when a potential difference is applied across the ends of a wire a constant electric field is generated ...
1
vote
1answer
245 views

Why the electric bulb turns on almost instantly when the switch is closed? [duplicate]

The electron drift speed is estimated to be very low.How could there is current almost the instant a circuit is closed?? By the discussions it is known that The information about beginning of the ...
4
votes
2answers
403 views

Why is the voltage drop across an ideal wire zero?

I'm having trouble conceptualizing why the voltage drop between two points of an ideal wire (i.e. no resistance) is $0~V$. Using Ohm's Law, the equation is such: $$ V = IR \\ V = I(0~\Omega) \\ V = ...
1
vote
3answers
2k views

Magnitude of magnetic field at the center of circular wire

I'm preparing for an exam by solving the sample questions , here is the one I'm having difficulty with : Following is the given circuit. Which contains two resistance $R_1$ and $R_2$ in form of ...
2
votes
2answers
133 views

What does E/M field look like when I close a circuit?

Suppose that we have a charged capacitor with two pins: $ C_+ $ and $C_-$. Suppose that we have a long wire with fixed geometry, that is already connected to the pin C+. Let the ...
2
votes
1answer
85 views

Inductor rise time and inductor wire length

So here is an interesting question about inductors or coils in general. Suppose you had a inductor which was 12 inch's in diameter and say 12 inch's in length and has 100 turns of wire. The total ...
1
vote
2answers
129 views

Cause of electromagnetic induction?

The rate of change of magnetic flux through a surface (open) is related with the line integral over the closed loop binding the selected surface by one of the Maxwell's equation. But that means even ...
18
votes
5answers
1k views

Does alternating current (AC) require a complete circuit?

This popular question about "whether an AC circuit with one end grounded to Earth and the other end grounded to Mars would work (ignoring resistance/inductance of the wire)" was recently asked on the ...
2
votes
1answer
323 views

Graphene batteries/super capacitors

A while ago, there was some news about micro-scale graphene-based supercapacitors and these devices can charge and discharge a hundred to a thousand times faster than standard batteries. Question: ...
1
vote
1answer
980 views

Why does the thickness of a wire affect resistance?

For small thicknesses of wire, it's pretty obvious why resistance affects thickness. (The electronics squeeze to get through). But after a certain thickness shouldn't the thickness become irrelevant? ...
2
votes
1answer
412 views

Is the standard explanation for the ring launcher incomplete?

Related: Faraday's law in a ring The ring launcher is a standard introductory physics demonstration that I assume almost everyone has seen (if not, YouTube it). The explanation of why the ring is ...
0
votes
4answers
1k views

Transformer: primary side & secondary side current 180 degree out of phase

I am a novice in electrical engineering. I notice that in transformer the secondary side current & current referred to as primary are 180 degree out of phase from each other. But why it is so, I ...
1
vote
3answers
223 views

potential difference problem?

As far as i know potential difference between 2 points is defined as the negative line integral of electric field between those 2 points. I also know that when magnetic field changes curl of electric ...
1
vote
1answer
167 views

Battery and current confusion?

How exactly does a battery produce a current in the circuit connected across its ends? I dont want to know the chemical reactions in the battery core, but just the essence of it. I believe it doesn't ...
0
votes
0answers
49 views

Blocking electro-magnetic waves between two near field antennas

Its been a while since I studied physics, so pardon my ignorance. I have two near field antennas. The range of the antennas is about 2-3 cm. I am looking for a way where I can block and unblock the ...