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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Why are charge (or current) and "amount of substance" both still base units even though charge is quantized?

Most unit systems have some dimension where charge or current is treated as a "fundamental" or "base" unit. The SI system is one familiar example. However, since Millikan's oil ...
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With a properly wired/grounded neutral wire, is it breaking ohm's law?

I have researched and asked some questions around this before, so let me explain. I understand by bonding an Earth ground (literally a green wire to a metal rod in the ground) to the neutral bus bar, ...
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How are the electrons able to overcome the significant force of attraction of the ions?

The cause of electrical resistance(in a metal) is electrons colliding with themselves and the positive ions. So if the electrons collide with the positive ions, how are they able to overcome the ...
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What is the definition of direction of current?

Wikipedia defines the direction of current as: The direction of conventional current is arbitrarily defined as the direction in which positive charges flow. But suppose a region where there is a non-...
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Why is the current equal when the resistors are in series? [duplicate]

I am a High schooler. And I learned that the current is always the same when the resisters are in series. I was told about the water analogy. If the first one had had a smaller resistance wouldn't it ...
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Potentiometer problem with two cells; determine the length where the jockey should meet the potentiometer wire [closed]

So the statement of the problem is "Find x such that the galvanometer shows zero deflection. Resistance of the potentiometer wire is 6 ohm." The answer to the problem according to the source ...
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I've been struggling with this question a lot any help would be highly appreciated [closed]

You make a parallel connection between two resistors, resistor A having a very large resistance and resistor B having a very small resistance. The equivalent resistance for this combination will be a) ...
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What is a cathode and an anode in general sense

i am totally confused and not able to understand the difference between cathode and anode Cathode is defined as reduction point but why is its sign -ve in a terminal and different in a battery Anode ...
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What is the precise definition of *direction* of current and of current element for a conductor?

The Biot–Savart law states that magnetic field due to an elemental cylindrical system through which a constant current $I$ is passing at a point $r$ distance away is given by $$d\vec{B}=\frac{\mu_o}{4\...
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Why is the magnetic field around a straight current-carrying wire in concentric cirlces?

I have a question that, why are the magnetic field lines around a straight current carrying wire in the form of concentric circles? If the wire is carrying current, it is acting like a magnet. So ...
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Is it reasonable to think charge as an energy carrier? Why?

I learned in physics that potential difference is the work done on unit positive charge going from the point of lower potential to the point of higher potential. And electromotive force is the energy ...
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How does the high potential difference between the two points ionizes the air?

As we can see that for some instance air can tolerate the potential difference between two points without any high leakage current and when this potential difference between the two points becomes too ...
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Explain "magnetic" deflection of a charge moving radially relative to a conducting wire in terms of relativistic effects

Apparently some people are unfamiliar with the concepts addressed in my question. I have found several videos on the topic. All of which follow the development I referenced in the Feynman Lectures. ...
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What will happen if both electrons and positive charges got ability to move inside the conductor?

Let's consider a conductor which has a potential difference across its ends. And let's say that the electrons which already have tendency to move inside the conductor, by all of a sudden if positive ...
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Does electric current actually depends upon the speed of flow of charges?

Electric current is the rate of flow of charges so can we say that it depends upon the speed of flow of charges (Is electric current directly proportional to speed of flow of charges). If this is true ...
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Apply superposition principle to compute current in the $2Ω$ resistor shown in the figure. All resistors are in ohms [closed]

So in this question what I tried to do was first remove the 6A source and then try to apply the current divider rule according to which the current I = 24 x (4/12) = 8A and then remove the 24A source ...
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How does the deflection of a compass increases if a current carrying wire is kept at the same point, but its current is increased?

In my physics book, there is an activity which explains how to draw magnetic field lines (which will be in shape of circles) of a current carrying wire using a compass. Later it says that if we ...
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Why does electric potential does not change along a wire(superconducting) but change across a resistance?

By the formula for electric potential $V=\frac{kq}{r}$ it is apparent that potential depends solely on the source charge and distance of a point from it and has nothing to with resistance. So when we ...
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Relativity and Electromagnetism: why doesn't every current-carrying wire generate a perpendicular electric field?

I was looking at Purcell's derivation of a current-carrying wire's magnetic field using the Lorentz transform, and noticed something which bothered me. It assumes that the distance between positive (...
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AC for Geissler Tube?

I could not find the answer anywhere so I am going to ask whether it is safe to operate a Geissler tube in AC instead of DC. I know that electrons get excited to a higher energy level by the high ...
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Can any constant power source be made independent?

The $V-I$ graph of a constant power source is a rectangular hyperbola with asymptotes as the $V$ and $I$ axes. Doesn't this mean that if we take a source giving, say the current in the pico-ampere ...
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Can a 9 V battery kill you?

Suppose I connect a 9 V DC battery to a DC-to-AC converter. Then connect the output of the converter to a step-up transformer, which increases the voltage to 2000 V. Now, if I put myself between the ...
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How does a resistor "know" to increase the potential difference across its ends?

My book says that current has to be constant throughout a simple series electrical circuit consisting of wires, a cell and few resistors, and hence resistors have higher potential difference across ...
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Confusion regarding drift velocity and potential

From this post I understood that the drift velocity of electrons decreases further into the circuit. But my book says that electrons move with constant velocity throughout the circuit, and both of ...
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Does the number of electrons colliding in wire get double as the length of wire gets doubled?

Does the number of electrons colliding in a wire get doubled when length of wire is made twice with its area of cross-section remain constant. My calculations for this are:- For wire of length $L$: ...
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Is it accurate to say that a step-up transformer reduces current?

Usually, it is said that step-up transformers are used to transmit power at high voltage and low current, so that $I^{2}R$ losses are minimum. But what does this "low" current actually mean? ...
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Does a higher voltage always mean a higher electric field strength?

In a step-up transformer, the output voltage is higher than the input voltage, while the output current is lower than the input current. Basically, since P = VI is conserved, the current has to ...
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Electric field inside current carrying conductor

Is the electric field inside current carrying conductor changing electric field or it is a constant electric field? And how this electric field produce magnetic field?
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Why reversing the direction of electric current reverses the magnetic fields' direction?

I don't understand why magnetic field gets reversed when the electric current is reversed. So I searched on the internet but couldn't find any answer. Could someone plz explain this phenomenon?(with ...
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EMF of source depends on the charge and the path then what do we mean when we say EMF of a source is $\epsilon$?

EMF of an EMF source (a battery for example) is defined as the work done by the non-conservative force(s) on charged particles as it passes through the terminals of the source divided by the charge of ...
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Current along a Resistor with variable resistivity in DC circuit

I had a question regarding the current along a resistor with variable resistivity. If you have a normal resistor with constant resistivity throughout its length, and you apply a constant DC voltage ...
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Why do these 2 formulas about magnetic field conflict with each other?

$\newcommand{\tl}[1]{\tag{#1}\label{#1}}$ Magnetic Field of a current is: $$B = \mu_0 I / (2 \pi r)\tl{01}$$ Magnetic Field of a Moving Charge is: $$B = \mu_0 qv\sin\theta / (4\pi r^2)\tl{02}$$ So I ...
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Does Resistance Affect Voltage?

I have looked this up and what followed was that resistance does not affect the voltage of a circuit. But lets say we have a power source of 5V flowing at 1 Amp. The neccesary resistance of this ...
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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 ...
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A question about power

Pardon me if this is too basic knowledge. It's been a while since my last Physics class in high school so a lot of the knowledge is no longer active in my mind. Here's the question. Say I have a ...
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We know that $R={\rho l/A}$ but how do you define L and A, Area of cross section?

How do we define area of cross section of a conductor for resistance of a metal piece. When you a wire which is generally cylindrical you have a length of it. Its area of cross section is a circle ...
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How does both laws helps in getting the magnetic field off axis inside a charged rotating ring about its centre [closed]

Consider we have a rotating charged ring (rotating about its centre) of radius $a$ what I'm trying to find is the magnetic field of a point $r$ from the axis in the plane for $r\ll a$. The sheet hints ...
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Why $V\propto R$ and $V\propto I$?

Ohm's law's gives us two relations: $V\propto R$ and $V\propto I$. But why is that so? Potential difference($V$) between two points depends on the concentration of charges between them. Current flows ...
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Why is the neutral wire safer than the hot wire when properly grounded? [duplicate]

So I looked this up in multiple places but could not get an answer that makes sense in my head. To be clear, I am not here to debate, but understand. Let's say I am not using any 240V circuits in my ...
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Why does current decrease when voltage is increased? (transformers)

Why is the current in the secondary coil less than in the primary when the voltage is greater in that coil as compared to primary coil? (for transformers) Well I know that energy should be conserved ...
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Why does current increase when area of cross section is increased?

When we increase the area of cross section of a wire, we find that with same voltage provided there is a twice amount of current flowing through resistor than before. Either you think that " this ...
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Electric potential and kinetic energy in any flowing charge

We just started with electricity in school(grade 10) and I have some confusions regarding electric potential. According to my book, The potential at a point is defined as the amount of work done per ...
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Which was the first experiment to demonstrate that current is the same as charge in motion?

I realized that I do not know the answer to this question because even in my first course in physics they presume that the student knows that charges are electrons and currents are moving electrons. ...
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Holding a multimeter with bare hands?

What will happen you'll hold both the metal part of the ends of multimeter each with one hand and check the voltage/current/resistance? While standing on insulated surface and ground both. Will the ...
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Equivalent resistance of this circuit, equality between two points confusing [closed]

Also, it is stated that the equivalent resistance between AC is same as that between BC. But $\frac{1}{R_{AC}} = \frac{1}{10} + \frac{1}{14}$ Which on looking and calculating is not equal to $R_{AC}$. ...
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Electric current - In a simple DC circuit does the return wire carry the same amount of current back to the battery?

A = Amperes as symbol. Take a simple DC current that has a battery, a light bulb, and to copper conductors. If the current coming out of the negative terminal of the battery. let's say 1 amp, but the ...
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Principle of working of a transformer [closed]

What is the principle of working of transformers? Magnetic effects of current Mutual induction Self induction Chemical effects of current I know that Mutual induction is the right answer, but isn't ...
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Why AC current lose less power over long distances than DC? [duplicate]

I was eager to know why AC current has a smaller power loss than DC over long distances. It depends on the fact that electrons aren't really going anywhere or it depends on other factors? Is there any ...
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Energy current in a quantum chain

I have seen in (e.g. this paper) the definition of the energy current in a chain with $H = \sum_{j=1}^L h_j$ where $H_j$ has support on the $k$ sites $j,j+1,j+2,...,j+(k-1)$ as $$J_j - J_{j+1} = i[H, ...
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How does the continuity equation mean that the charge is conserved in the neighbourhood of any point?

I am currently studying the textbook Principles of Optics: Electromagnetic Theory of Propagation, Interference and Diffraction of Light, 7th Edition, by Max Born and Emil Wolf. In section 1.1.1 ...

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