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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20answers
22k views

Why doesn't current pass through a resistance if there is another path without resistance?

Why doesn't current pass through a resistance if there is another path without resistance? How does it know there is resistance on that path? Some clarification: I understand that some current will ...
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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 ...
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Why is the ampere a base unit and not the coulomb?

I always thought of current as the time derivative of charge, $\frac{dq}{dt}$. However, I found out recently that it is the ampere that is the base unit and not the coulomb. Why is this? It seems to ...
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What *exactly* is electrical current, voltage, and resistance?

I am taking AP Physics right now (I'm a high school student) and we are learning about circuits, current, resistance, voltage, Ohm's Law, etc. I am looking for exact definitions of what current, ...
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Why is AC more “dangerous” than DC?

After going through several forums, I became more confused whether it is DC or AC that is more dangerous. In my text book, it is written that the peak value of AC is greater than that of DC, which is ...
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3answers
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Will the volt, ampere, ohm or other electrical units change on May 20th, 2019? [duplicate]

When watching a video by Veritasium about the SI units redefinition (5:29), a claim that the volt and unit of resistance (presumably the ohm) will change by about 1 part in 10 million caught my ...
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Speed of light vs speed of electricity

If I arranged an experiment where light raced electricity what would be the results? Let's say a red laser is fired at the same time a switch is closed that applies 110 volts to a 12 gauge loop of ...
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Birds on a wire (again) - how is it that birds feel no current? They are just making a parallel circuit, no?

I have been thinking about this and I know that other people have answered this on here, but there's one part that still baffles me, and it has to do with parallel circuits. If I connect a battery ...
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If electrons are identical and indistinguishable, how can we say current is the movement of electrons?

When we talk about current, we say electrons are "flowing" through a conductor. But if electrons are identical particles, how does it make sense to talk about them flowing? To expand on that:...
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If the Earth is a good conductor of electricity, why don't people get electrocuted every time they touch the Earth?

Since the Earth is a good conductor of electricity, is it safe to assume that any charge that flows down to the Earth must be redistributed into the Earth in and along all directions? Does this also ...
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Is electricity really the flow of electrons or is it more involved?

I am new to the physics category of the Stack Exchange site. I apologize if my question is wrong, too broad, simple, or worded incorrectly. I am just trying to figure out what is true and false when ...
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Why is current a scalar quantity?

Current has both magnitude and direction. As per the definition of vector defined in encyclopedia, current should be a vector quantity. But, we know that current is a scalar quantity. What is the ...
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4answers
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How do electrons know which path to take in a circuit?

The current is maximum through those segments of a circuit that offer the least resistance. But how do electrons know beforehand that which path will resist their drift the least?
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Could someone intuitively explain to me Ohm's law?

Could someone intuitively explain to me Ohm's law? I understand what voltage is and how it is the electric potential energy and that it is the integral of the electric field strength etc. I also ...
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Photoelectricity in daily life

Photons strike metals innumerable times in our day-to-day experience.Then, why photoelectrons do not come out of metal surface and cause current?
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10answers
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Is every open circuit a capacitor?

I think that even open-ended wires can let AC current flow through them, just with a low capacitance. I also think an antenna could be a capacitor and open ended. Am I thinking correctly?
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How does electricity propagate in a conductor?

On a systems level, I understand that as electrons are pushed into a wire, there is a net field and a net electron velocity. And I've read that the net electron drift is slow. But electricity ...
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Is there a simple proof that Kirchhoff's circuit laws always provide an exactly complete set of equations?

Suppose I have a complicated electric circuit which is composed exclusively of resistors and voltage and current sources, wired up together in a complicated way. The standard way to solve the circuit (...
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Speed of electrons in a current-carrying metallic wire: does it even make sense?

Does it make sense to speak about the speed of electrons in a current-carrying wire (non perfect conductor)? If so, what is their speed? Here are my thoughts: On the Internet (Wikipedia, ...
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Does Ohm's law hold in space?

My current understanding is this: When current passes through a resistor heat is generated which the resistor then gives off to the surrounding air. That way the resistor is kept at roughly the same ...
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4answers
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Why don't loop currents produce light?

If a charge travels in a circle it must accelerate, thereby producing EM. However, a wire in a circular loop is analogous to many charges moving in a circle. So, why don't circular currents produce ...
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6answers
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Will current pass without any resistance?

I've learned that a resistor converts some electrical energy into heat energy while the current flows through it and thus causes a power loss, but what if there's not any resistor in a circuit. Will ...
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In aluminum, how does electricity travel through the surface oxide layer?

Suppose I connect a conductive wire (cross section 1 mm$^2$) to an aluminum object. Since aluminum is highly conductive, electricity will flow smoothly inside the object with little resistance. ...
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9answers
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The water analogy seems to imply that power = current. Why is this incorrect?

Many people think of the water analogy to try to explain how electromagnetic energy is delivered to a device in a circuit. Using that analogy, in a DC circuit, one could imagine the power-consuming ...
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8answers
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How can a battery charge up another battery to a higher percentage?

Say I have my phone on 5% and a large battery pack on 35% and I charge the phone. By the end the phone is on 100% and the pack is on 12%. How can the battery pack charge the phone up to a higher ...
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6answers
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In an alternating current, do electrons flow from the source to the device?

If electrons in an alternating current periodically reverse their direction, do they really flow? Won't they always come back to the same position?
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3answers
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Can a superconducting wire conduct unlimited current?

A superconducting wire has no electrical resistance and as such it does not heat up when current passes through it. Non-superconducting wires can be damaged by too much current, because they get too ...
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Is everything a resistor?

Resistance is due to collision with protons, and pretty much everything contains protons. So technically is everything a resistor? (Or at least, can anything be a resistor?)
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6answers
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How is possible for current to flow so fast when charge flows so slow?

How is it possible for current to flow so fast when charge flows so slowly? We know electrons travel very slowly while charge travels at ~the speed of light.
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Why does vacuum have a nonzero characteristic impedance towards electromagnetic radiation?

On Wikipedia, the impedance of free space $Z_0$ is defined as square root of the ratio of the permeability of free space $\mu_0$ to the permittivity of free space $\epsilon_0$, i.e. $$Z_0 = \sqrt{\...
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Why is current the same in a series circuit?

So I am a 10th grade student and my teacher told me that the current is the same at every point in a series circuit. It does split up in parallel circuit but it then recombines and the current flowing ...
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How does a wire carry alternating current?

Consider a simple network of a bulb whose two terminals are connected to two wires with open ends A and B respectively A o--------💡--------o B Now if a DC ...
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3answers
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Why is ampere still a base unit? [duplicate]

The ampere is still a base unit, according to the SI brochure. However, in my perception the recent redefinition of units effectively defines the Coulomb as e/(1.602 176 634 × 10^−19), and the ampere ...
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7answers
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Why do bulbs glow brighter when connected in parallel?

Consider a circuit powered by a battery. If light bulbs are attached in parallel, the current will be divided across all of them. But if the light bulbs are connected in series, the current will be ...
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Why do birds sitting on electric wires not get shocked?

When we touch electric wires, we get shocked. Why don't birds sitting on electric wires not get shocked?
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Do the integral forms of Maxwell's Equations have limited applicability because of retardation?

In the usual bookwork treatment, it is easy to show that the differential and integral forms of Maxwell's equations are equivalent using Gauss's and Stokes's theorems. I have always thought that ...
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3answers
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Tree vs lightning rod: why does one burn and the other not?

I have this simple question, but I cannot find the answer. I saw this video about a plane getting hit by lightning. In it, Captain Joe explains why people do not get electrocuted. This has a simple ...
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3answers
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Does current run forever in water? (assuming the supply voltage is there forever)

Suppose pH of water is $6$, I think this means there is one $\text{H}^{+}$ ion for every $10^6$ water molecules. When we plug in the battery, I believe we see a current as the $\text{H}^{+}$ ions ...
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Why the electrons below the Fermi level do not conduct electricity?

Physically, why is it that the electrons need to excited above the Fermi level to conduct electricity? In other words, why is the current zero when the electrons lie below the Fermi level? Does Pauli ...
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3answers
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Where do electrons in electricity come from?

Where do the electrons come from when an electric generator is making electricity? Is from the air? Would a generator work in a vacuum? Electrons have mass so where would they be pulled from if ...
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Intuition behind Faraday's Law?

Faraday's Law seems more like an observation than an explanation. Sure, a changing magnetic current causes emf, but why? How does a changing magnetic field cause electrons to move in the direction of ...
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4answers
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How can one derive Ohm's Law? [duplicate]

I am looking for the derivation of Ohm's Law, i.e., $V$ is directly proportional to $I$. Can someone help me with it?
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Why isn't current carried through a vacuum?

The empty vacuum of space shouldn't offer any resistance to a travelling electron, and so a large collection of electrons should similarly travel through a vacuum without resistance. As a result, the ...
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Current without Voltage and Voltage without Current?

At school I've always learned that you can view Current and Voltage like this: The current is the flow of charge per second and the Voltage is how badly the current 'wants' to flow. But I'm having ...
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Why does current density have a direction and not current?

Current is a scalar $I$ with units of $\mathrm{[J/s]}$. It is defined as $I=\frac{\mathrm{d}Q}{\mathrm{d}t}$. Current density is a vector $\vec{J}$ (with magnitude $J$) with units of $\mathrm{[J/s/m^2]...
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Do moving charged particles have both magnetic and electric fields?

Consider a charged particle (electron or proton) at rest. It is surrounded by its own electric field. Now consider an electron moving with certain velocity. Is there still an electric field around it?...
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Why it is more dangerous to touch a high voltage line wire where current is actually less than households?

I have seen that power is transmitted from power stations to households at high voltage and low current to minimize the power loss. That means the current in the transmission line is less than the ...
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6answers
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If voltage is same in two points why does electron move? [duplicate]

We know that at point A and B there is same voltage.Then why electron moves from one point to the another one?
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8answers
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Understanding voltage and power in the fluid analogy for DC circuits

I am trying to understand electric circuits (ie voltage, current, power, and resistance). For the most part, everything makes perfect sense, but for some reason I do not feel as if I understand the ...
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What's the reason behind the current remaining the same after passing by a resistance?

I've been wondering why does this really happen, I mean by intuition if electrons are driven by EMF (ignoring wire's resistance), $n$ coulombs would pass by a point per second, until they encounter ...

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