# Questions tagged [electric-current]

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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### Finding the voltage across $R_3$ [closed]

I have the following circuit. $V_B = 18V, R_1=3k\Omega, R_2 = 6k\Omega, R_3 = 10k\Omega, R_4 = 1k\Omega \text{ and } I_A=1,2mA$. What's the value of $V_4$ here?
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### How does a voltage source know what intensity to give? How much time does it take to measure and know? [closed]

as the title says, how does a battery use V = IR in measuring the intensity it would give, or is the voltage the variable here? if it's the voltage, what does that even mean?
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### Can you charge a capacitor with only voltage (without current)? If No, then how does a capacitor correct power factor?

Let me explain you why I am asking this question. The other day I was studying about power factor correction of a (step up or any) transformer. It said that on the output side of transformer's ...
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1 vote
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### Is current density always constant for an isotropic conductor of any shape?

I came across this question online, and I was just thinking how to find the transverse voltage ΔV. If we divide the large semicircular strip into very thin semicircular strips of width dx, then the ...
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### Does current flow equally through the cross section of a wire in DC?

(Most Probably a duplicate, but I couldn't find it) I have heard about 'Skin Effect' in AC, but currently Im only and only concerned about DC. When current flows in simple DC circuit, does the current ...
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### Photoelectric effect and frequency

Give an isolated photo tube and with a small emmiter and very large collector (no electron escapes) As one increase the frequency, one is also increasing the kinetic energy of photo-electrons and that ...
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### The flows of electrons when the voltage is zero [duplicate]

As we understand, electrons can't be unmoving therefore electrons always moving or flowing. If the voltage is zero, where do the electrons move? Do they move everywhere?
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### Current in a cube resistor [closed]

I am given this cube of resistors, each with the same resistance of 4 Ω. The current that enters at E and leaves B is 6 A. I have found that the equivalent resistance is 3 Ω. However, I am unsure of ...
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### How is 'exactly all' the energy of battery converted to thermal energy?

When charges flow in a simple circuit, then if 5C of charge is transported by the battery(of 5V) in some time, then the work done/energy lost by the battery is 25Joules. During this time, the ...
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### Variation of Resistivity After The DIELECTRIC BREAKDOWN VOLTAGE Is Applied

I want to know how a material's resistivity changes after the dielectric breakdown voltage is applied and crossed. Let's say for a circuit after air becomes a conductor for E=30kv/mm what would be the ...
1 vote
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### If I spin a magnet in a coil which has a length parallel to the magnet’s spin axis, is a magnetic field generated along the length of the coil?

This I feel is a bit of a complicated question, so I’ll quickly try to paint as clear a picture as I possibly can: The magnet is spinning on an axis perpendicular to its poloidal axis (the line which ...
1 vote
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### Power dissipated in a circuit

If total power dissipated in a DC circuit is given by $P = VI$ and power dissipated as heat is given by $P=I^2R$, since these are numerically equal, wouldn’t that mean all the power is dissipated as ...
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### Stationary charge near a current carrying wire: Experiment to check it at home

From what I have read so far, I arrive to a conclusion that a stationary charge must experience a force when it is near a current carrying wire. A stationary electron should get attracted and a ...
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### Why does a bulb not glow when one terminal of a bulb is connected to the negative terminal of a battery and other is connected to the ground?

I am a high school student and has been wondering a while about this: Why does a bulb not glow when one terminal of a bulb is connected to the negative terminal of a battery and the other is connected ...
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### Why won't the bulb light? [closed]

Here's what the marking scheme says: "Capacitor gets charged first and acts as an insulator/blocks current". However, electrons flow from negative to positive, so shouldn't the electrons ...
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### Max value of I in a circuit

I am a EE student.I have been taught Ohm's law which says $I = \frac{V}{R}$.In the limit of$R \rightarrow 0,I \rightarrow \infty$.But I have also taken the course "Electromagnetism II" where ...
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### What is $\gamma\lambda_0$ as given in the chapter Relativistic Electrodynamics of Griffiths

According to Griffiths (Chapter: Electrodynamics and Relativity, Section: Relativistic Electrodynamics)- We have a string with positive line charge $\lambda$. And on the same string a negative line ...
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### Is charge accumulated when two conductors of different resistivity placed in series in an electric circuit?

Let's say two long cylindrical conductors of resistivity ρ1 and ρ2 are joined together and a current I is flowing uniformly through the cross section So if we consider this scenario two different ...
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### How to get the temperature out of Joule heating equation?

The Joule heating law is defined as Voltage U times current I $P = U \cdot I$ Out of this you get the energy by multiplying it with the time $Q_e = P \cdot t$ and consequently you get the temperature ...
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### What is the electrical influence of a magnetic field on alternating currrent

Assume we put a very strong permanent magnet close to an AC carrying wire. What would the electrical effects on the wire be? Would there be any impedence or extra resistence caused? Could a permanent ...
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### Why is the polarity of an inductor same as that of the source voltage when a pure inductor is connected to an AC generator?

An inductor is connected to an AC generator. Suppose no resistance or capacitor is connected to that circuit. Then as per the lesson in khan academy, it's said that the inductor and the source voltage ...
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### If electric field inside a conductor is always zero, then why do free electrons move?

Electric field inside the conductor is zero. That means there is no electric force on electrons inside. Then how do free electrons move from atom to atom in random direction? What is the reason of ...
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### Why is collector-emitter breakdown voltage (open base) lower than the collector-base breakdown voltage (open emitter)?

I need to understand why the collector base breakdown voltage is greater than collector emitter breakdown voltage. Can it be analyzed from the energy band diagram so as to remember it mnemotechnically?...
1 vote
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### How can DC current arise? [migrated]

I'm curious to understand the properties behind direct current (DC) and alternating current (AC) which started when reading the definition and several articles online that, "AC periodically ...
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The conductivity formula is as follows: conductivity = (length)/(resistance * area). Let's say we want to measure the conductivity of a cubic material that consist two equal halves of different metals ...
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### Short diode current boundary condition

Suppose we have a "short" diode of lenght $W$: In order to derive current equation, the following boundary condition is used: $$\Delta p(W) = 0$$ ,where $\Delta p(W)$ (or the $\Delta p$ on ...
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### Why constant voltage applied to pn-junction produces constant current throughout the junction?

Is this assumption just something that turns out to be experimentally valid or there is at least some mathematical model like Kronig-Penney + some statistical mechanics that is able to give a good ...
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### Energy conversions in Electric furnace

Heating furnaces use eddy current to work, but I have a problem understanding something, what are the energy conversions that happen in the electric furnace? Is it magnetic->electric->thermal or ...
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### What would happen if an electrical current was passed through a black hole?

Can black holes conduct electricity? And if so, how effectively?
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### Average of calculated quantity of discrete data

Let's say I have two discrete series of a physical quantity, current I and voltage V taken at the same time interval in a DC circuit. Now, I want to estimate the average power P over N measurements, ...
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### Effect of solenoid on iron core in ac and dc circuit [closed]

If i have 2 insulated coils and i wrap each one of them on a iron core (i have 2 seperate ciruits) if i add a dc source “battery” in the first circuit and an ac source in the second circuit would ...
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### Potential drop against internal resistance of cells in combination

Suppose two cells of emf and internal resistance e1, r1 and e2, r2 respectively are connected in series. The negative electrode of 1st cell is connected to negative electrode of the second cell. Why ...
1 vote
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### Functional form of fluorescent light flicker in time

I will start with the disclaimer that I am a mathematician and do not know much about physics. I am interested in modeling light emitted from fluorescent bulbs and am curious about the relative ...
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### Bandwidth of LCR circuit [closed]

I'm trying to derive the expression of half-power bandwidth of LCR circuit but I'm struck. My approach: Let resonance frequency $ω_0 = \dfrac 1{LC}$ and peak voltage at resonance be $V = IR$ where $I$...
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### About kinematics of electrons in a circuit

We know that electrons flow in a circuit due to the electric field, so shouldn't the electrons be accelerating, but we also know that $i=neAv$ so from here we can conclude $v=i/neA$ which is a ...
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### WIll maintaining the ratio of 'Voltage/Resistance' violate Ohm's Law?

In an ohmic conductor if voltage and resistance are increased in a constant ratio, the current will remain same and if it remains same, won't it violate the Ohm's Law? As because Ohm's Law states '...
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### How to measure voltage induced in coil due to an oscillating bar magnet using null method? [closed]

Here we're trying to measure the maximum emf induced in the coil using null method. I can understand what the book means by 'a kick'. I can't understand how this circuit works. For example, how is the ...
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### Why doesnt potential divide in parallel circuits?

My initial question was why potential doesnt split in a junction in parallel connections. Say we have resistances R1 and R2 which are in parallel, and a cell that is in parallel with them. Let the ...
1 vote
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### Why doesn't coil in an Ac generator not get deflected in accordance to the flemming's left hand rule when current starts to flow through it [closed]

Why doesn't coil in an Ac generator not get deflected in accordance to the Flemming's left hand rule when current starts to flow through it. When the coil is ...
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### Do attracted to electrode charged particles make current?

Consider a bulb with an anode. Cathode, is out of bulb. Bulb is filled with gas. Now, gas molecules are ionized by, for example external radiation. Bulb should now contain "free" electrons, ...
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### Propagation of electric fields in circuits: lack of conceptual understanding [closed]

I have trouble understanding some fundamental properties about electricity and have the following conceputal questions: Say that we have a small battery (for example 1 V) and an very long wire made of ...
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### Diode $I$-$V$ characteristic for inverse region

This is the Shockley equation for the current of the diode: $$I_D = I_S \left( e^{\frac{V_D}{nV_T}} - 1 \right)$$ It is also valid for $V_D < 0$, when this equation tends to be $$I_D = - I_S$$ ...
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### How can heat generation be $V*I$ when the total power available to a circuit is $V*I$?

If joules law says rate of heat generation in a circuit is $V*I$, but the total power available to a circuit is also $V*I$, then all power in a circuit must go to heat. How can this be possible if a ...
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### What does stand behind the formula: "watt = ampere * volt"?

I know the "watt = ampere * volt" formula, but I don't understand what it means. So, let's start from the beginning. Coulomb answers the question: how many electrons do you have (in a ...
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### Current in a Nonuniform Diameter Wire

According to the text Current depends on Area, but then in problems with a "nonuniform diameter" we say that the Current does not change even though the Area changes. I think I understand ...
1 vote
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### Power consumed by an electrical load

I saw this quote on a website recently: "A fundamental law of electric circuits is, that because current must be constant all the way around a circuit, only half the power of a generator can be ...
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### Magnetic Field Strength $B$ of a Wire

I understand that magnetic field strength $B$ decreases by 2 pi r assuming I and permeability is constant. Is r assumed to be from the edge of the wire or the centre of the wire? If it is from the ...
1 vote
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### In real life, which remains the most constant: voltage, current or resistance?

According to ohms law, V=IR, where R is constant If the resistance of a circuit changes due to change in its physical conditions like temperature, etc. What will change-current or voltage?? Does the ...
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