A measure of the rate at which electric charge is transported (especially through a circuit), it has units of charge/time.

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2answers
30 views

Can charge flow to a neutral body?

If an electrically positive object is kept with a neutral object, in which direction will charge flow? Will charge flow from positive to neutral until both have equal charges, or will nothing happen ...
4
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2answers
571 views

What happens when you pass a current through a coil made of a ferromagnetic substance?

I know when you pass a current through a length of copper coil or a solenoid, there is the induction of a magnetic flux. But what of the coil made of the ferromagnetic material, the permanent type ...
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1answer
83 views

What is wavelength of electric field generated in a wire? [closed]

I read link given below: http://en.wikipedia.org/wiki/Speed_of_electricity Above link says _The speed at which energy or signals travel down a cable is actually the speed of the electromagnetic ...
3
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1answer
23 views

Half deflection in a galvanometer [on hold]

Why is half deflection taken while measuring the resistance of a galvanometer? Can't we take deflection in other ratios? Please help. I meant to ask while taking out the shunt resistance, why do we ...
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1answer
415 views

How is current produced in semiconductors or metals?

I think current is the movement of electrons through the wire or semiconductor, thus when I press the switch of the light bulb the electrons go from positive part to tungsten and light is produced. ...
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2answers
21 views

Short circuit due to loose terminations

I have been reading into wiring and circuits and found someone post that they had a circuit breaker tripping because of a loose wire in the circuit. They claimed the hot screw/lug combination ...
1
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1answer
376 views

Induced electric field due to a moving wire

An infinite wire carrying a constant current $I$ in the $\hat{z}$ direction is moving in the $$y$$ direction at a constant speed $v$. Find the electric field, in the quasistatic approximation, at the ...
1
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1answer
26 views

Does a capacitor experience a Newtonian reaction when being charged?

Say I have a capacitor that is being charged with a battery. There are two wires, one on the positive and one on negative terminal of the battery which go to a capacitor. During the charging, a ...
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2answers
33 views

Ohm's law experiment

I was going through my physics laboratory manual. In the Ohm's Law Experiment, the book states a few precautions without any reasoning. 1.The wire whose resistance has to be determined should ...
3
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2answers
46 views

How can “…electrons flow in metals, but not in the ground…” explain grounding rods?

I really enjoyed Why is the charge naming convention wrong? But, in the comments at the very end, the statement that "...electrons flow in metals, but not in the ground..." left me uneasy. I was ...
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3answers
198 views

Optimal method for solving circuit

This problem seems quite simple, and I can easily find a way to solve it but the possibility of error in my method is extremely high. This is just a sub-task of a bigger task but this is the only part ...
0
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4answers
6k views

Relation between Power, Voltage and Current when one or more of them is amplified?

$$\text{Power}(P) = \text{Voltage}(V) \cdot \text{Current}(I)$$ If voltage or current is amplified or multiplied what happens to power and current. Does this affect in increase or decrease in power ...
2
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2answers
117 views

How to find the direction of an eddy current?

Suppose there is a magnetic field going from left to right. Suppose a thin sheet of metal conductor (e.g. a 1m*1m square) is dropped through the magnetic field such that the plane of the conductor is ...
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2answers
211 views

Close or open circuit?

A electric source provides a non electrostatic influence on the charges inside the source which pushes the positive charges from the negative terminal to the positive one. Does this happen when the ...
1
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1answer
24 views

Why is power dissipated in a circuit maximum when external resistance is equal to the internal resistance in the circuit? [on hold]

[![question 24][1]][1]Suppose in a circuit the battery has emf 6V and internal resistance 3ohm. It is connected to an external resistance = R ohm. According to my ...
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2answers
548 views

How is the 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 ...
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1answer
17 views

If we increase dimensions of a wire, how does electron density change?

If we increase the diameter of a wire, does the electron density change at all? When we increase the diameter or the length of a wire (while solving numericals) do we add appropriate number of ...
1
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1answer
113 views

Current in discharging capacitor through fixed resistor?

In the textbook I'm using for physics it says that the charge left on the plates of a capacitor after time $t$, that is discharging through a fixed resistor, is $Q=Q_0e^{-t/\tau}$ where $\tau=RC$ is ...
0
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1answer
178 views

Opacity/transparency of conductive meshes to charged particles (electrons/ions)

When using a conductive (metal) mesh, effectively a metallic woven fabric, in vacuum applications as a "grid" for charged particle optics, how does one calculate (or at least estimate) the opacity or ...
4
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2answers
83 views

Why is Kirchoff's Current Rule valid?

The fact that Kirchoff's Current Rule is valid means that whatever current flows in flows out. But this will only be valid for a steady current circuit, that is, when there is no accumulation of ...
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0answers
15 views

How to apply kirchoff's laws to motors in DC and AC settings

DC case: is it ok to treat a motor as a variable resistor, with resistance depending on the load? AC case: suppose I have a motor that runs at 120V AC and is rated to X watts, how can I determine how ...
0
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2answers
185 views

Current on both sides of a capacitor

When a capacitor is connected to a DC circuit, what ensures that the current on both sides of the capacitor is the same? When charges arrive at one end of the capacitor they stop moving; presumably ...
2
votes
2answers
240 views

Photoelectric effect stopping potential

$q_eV_s = hf - \phi$ My question is... suppose we are testing the photoelectric effect. One plate is illuminated. We have applied the stopping potential. Suppose an electron leaves one plate with $KE ...
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2answers
44 views

Some questions related to circuits and flow of electrons

I have some doubts related to electric fields and flow of current. So, let us assume an electric circuit, which contains a battery and a wire connecting positive and negative terminal of the battery. ...
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8answers
22k views

Why is the charge naming convention wrong?

I recently came to know about the Conventional Current vs. Electron Flow issue. Doing some search I found that the reason for this is that Benjamin Franklin made a mistake when naming positive and ...
0
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2answers
292 views

How does back-emf oppose the input-current?

A circuit, has current $A$ flowing at a certain $V$. When there is a change in magnetic-flux, based on Faraday's law of induction & Lenz's law, we know that there is change in Potential ...
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1answer
112 views

Spherical magnet inside a solenoid

When passing a bar magnet through a long solenoid why is it that the induced emf when the magnet is in the middle of the solenoid is zero? And if a spherical magnet is put inside the solenoid, will ...
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1answer
423 views

How to calculate flux density in a toroidal CT that has an electrical line pass through the center?

I have seen the Biot–Savart equation, but I don't know how to apply it. Does the conductor length need to be considered finite and equal to the core length, or will the calculation be for a conductor ...
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2answers
43 views

What is meant by “current” in this context?

This is a quote from Optics by Hecht: A stationary charge has a constant E-field, no B-field, and hence produces no radiation—where would the energy come from if it did? A uniformly moving ...
3
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1answer
25 views

Why can't we use Meterbridge to measure high resistance and low resistance?

Our physics master taught us that we can't use meterbridge to measure low resistance but he didn't give a valid reason for that.
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0answers
14 views

(boundary conditions) Interface between two lossless media

I'm wondering why there's usually no free charges nor free currents in the interface between two lossless media? no free current "I guess" is due to the insulating nature of a lossless media but why ...
2
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4answers
804 views

How to use Ampere's Law for a semi-infinite wire with current?

Suppose that there is a semi-infinite wire which extends to infinity only in one direction. There are no other circuit elements at the other end(finite end) of the wire and the current does not loop. ...
0
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1answer
737 views

Mean-free-time between collisions and drift-velocity

In a physics text book I need help to make sense of the part highlighted in yellow: This is out of context of course, so just to make it clearer: $\tau$ is the mean free time of the electrons in a ...
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0answers
23 views

Force Exerting on a magnetic train

A question is already asked ( How does this “simple” electric train work? ). But I've got a question about it. In order to calculate the force which is being exerted on the system including magnets ...
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0answers
20 views

How do electrons choose their way through nodes? [duplicate]

Suppose I have a circuit, powered by some emf ($V$). If I put two resistors $R1$ and $R2$ of different resistances in parallel, the current at the node is divided following Kirchhoff's circuit laws. ...
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1answer
308 views

The image current due to moving charges and a current carrying thin wire

Suppose we have a plane conductor and positive charged particles of mass m are moving parallel to the plane conductor at a distance d. The trajectory can be assumed to be straight. An image current ...
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0answers
33 views

induced current in loop

I'm re-asking this question that was posted by @zhzh and subsequently closed. If you have a loop that is spun clockwise as a magnet is moved near it, is a current induced in that loop? If the ...
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2answers
578 views

Is it possible to use induction ampermeter to measure power consumption of electric water heater and dryer?

I hope this practical question is not OT and not too trivial for this forum. I am renting an apartment in a duplex with a shared water heater and dryer. Turns out, both water heater and the dryer are ...
3
votes
2answers
199 views

Ampere's law of circular path when “bulging” out

The picture shows a use of Ampere's law. A circular path is chosen. $$\oint \vec B \bullet \mathrm{d}\vec l=\mu_0 I_{encl}$$ When using Ampere's law we are talking about the current enclosed. That ...
3
votes
3answers
5k views

Non-conservative electric fields due to changing magnetic flux?

What I read in several places, tells me that, the fact Coulomb's Law follows inverse-square law and gives a force which is radial, implies that a static electric field must be conservative.(In short, ...
1
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1answer
243 views

Which power equation to use: $P = I^2 * R$ or $P = V^2 / R$?

Given are ideal max voltage $V = 200\;\mathrm{V}$ and max current $I = 5\;\mathrm{A}$. Therefore: ideal resistance is $$R = \frac VI = \frac{200 \;\mathrm{V}}{5\;\mathrm{A}} = 40 ...
0
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1answer
205 views

How is Magnetic force on a current carrying conductor $Blb$

I was reading an answer about torque acting on a rectangular current carrying loop kept in a uniform magnitude field B. Force acting on each sides is $F_1$, $F_2$, $F_3$, $F_4$. It's written here : ...
3
votes
1answer
533 views

If I charge a battery using a much higher current, can it explode?

If I have a 12V 4Ah lead acid battery and use a battery charger that, let's say for example, can charge 10A, 50A, or 100A. If I theoretically turned it to 100A will the battery explode? I understand ...
1
vote
1answer
641 views

Forces on a wire moving in a magnetic field?

When a wire is placed inside a magnetic field and current starts to flow in that wire, that wire experiences the Lorentz force = $IL \times B$ and beings to move. Aside from induced motional - ...
0
votes
2answers
213 views

Drift Speed and Current in Two Different Inertial Frames

We have a long, cylindrical wire carrying a constant current I in an inertial frame. At a distance of R from the center of the wire, the magnitude of magnetic field is $μI/2πR$. What is the magnitude ...
1
vote
1answer
28 views

If steady current flows in a metallic conductor of non uniform cross section area then why is current constant? [duplicate]

If area is not uniform then how can current be constant? What happens to current density, electric field, drift speed? Are they constant?
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2answers
30 views

Why does current density changes but not current? [closed]

let us assume that we have a conductor with a specified resistance ( case 1 ) and a normal conductor ( case 2 ) as shown in the figure , and now we apply an external electric field with a battery on ...
2
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0answers
31 views

Electric field due to a current carrying loop

I want to know how I can calculate the radiated electric field in the far zone of the loop. Knowing that the loop is in center at the origin of a x-y plane Knowing that the loop as a time-harmonic ...
0
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1answer
40 views

Electric field along a wire and load

I have referred to many books and all of them apply loss in potential across a resistor only in case of circuits. However, the electric field is present in the whole conductor. Hence the electrons ...
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2answers
1k views

A confusion in ohms law $V = IR$

ohms law clearly states that potential difference is directly proportional to the current flowing through the wire or V directly proportional to I ______(i) so the formula which is ...