The current tag has no wiki summary.
3
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3answers
409 views
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 ...
4
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2answers
194 views
How can I cause a levitating magnet to rotate?
I have a device like this one:
http://www.youtube.com/watch?v=kA_hw_lY-OY (All of them work the same)
Here's an image:
I want to make it spin without touching it with hands.
I tried using magnets ...
0
votes
2answers
211 views
What is the meaning of the gradient of a current vs time graph?
What is the meaning of the gradient of a current vs time graph?
In other words, what does the unit $As^{-1}$ or $Cs^{-2}$ represent?
0
votes
1answer
153 views
How do I solve the current of this resistor using Maxwell's Current Theorem?
I've been trying to solve this using the method the prof. taught us, and I happen to know the answer but I can't reach it no matter how many times I've tried. The circuit in question is below:
I am ...
2
votes
3answers
403 views
Root mean square value for DC
The mean value of alternating current comes to be zero because of half of the cycle being positive while the other half negative. so, take the root means square value of Alternating current given by:
...
2
votes
3answers
662 views
is it possible to flow current in open circuit?
First , i don't know much about chemistry and physics. I'm just a graphic designer but i have this question in my mind. I'm sorry if this question is too basic and use 'generic' language.
As i know ...
4
votes
2answers
322 views
How to calculate required current and specifications for a “wet coil” to generate x Tesla of magnetic field?
A water management project requires a "wet coil" (coil will be submerged in aqueous media) designed to generate a steady-state electromagnetic field of adjustable magnetic magnetic flux density at the ...
4
votes
0answers
235 views
Relating the variance of the current operator to measurements
(EDIT: Thanks to Nathaniel's comments, I have altered the question to reflect the bits that I am still confused about.)
This is a general conceptual question, but for definiteness' sake, imagine a ...
1
vote
0answers
122 views
If we have a current I flowing down a wire, why must the net bound current be zero?
Say we are dealing with a wire that has a current I flowing through it, i.e. I is the free current. Why must it then hold that the net bound current, that is, the bound volume current, $J_b$, and the ...
6
votes
2answers
268 views
How electric currents can flow between 2 points at the same potential?
According to Ohm's law, if there is a potential difference, $V$, across a resistor then there is a current, $I$, flowing through it.
Since we assume that points along the connecting wire are at the ...
0
votes
2answers
550 views
Confusion about P=VI and V=IR
If we look at $P=VI$, we see that if the current doubles then the potential difference is halved
but this doesn't seem to make sense according to $V=IR$. If we look at that equation, since the ...
-1
votes
2answers
93 views
What is current of electric circuit which has only one component - a battery (or cell)? [closed]
What is current of electric circuit which has only one component a battery (or cell)? Explain why.
1
vote
1answer
115 views
Electromotive force
EMF is defined as:
"The potential difference across the terminals of a battery or dry cell when it is giving no current to the circuit."
So, if current starts to flow from the ...
4
votes
4answers
371 views
Are square wave really square or are they always relative approximations using harmonics
I'm studying the properties of waves through different mediums, and got hung up on this.
Is a square wave always a sum of harmonics or can we produce a square wave by quickly changing voltage? Is ...
1
vote
0answers
104 views
What is the weakest magnetic field that can practically be measured?
I would like to be able to measure magnetic fields that are generated by nerve impulses in extremities like in fingers.
I know that they are very weak: about 100 mV electric potential would give us ...
1
vote
2answers
716 views
Basic questions about voltage drop in DC circuit
I understand all the concepts of what voltage is using all the analogies but some things related to the drop of voltage across a circuit confuses me.
If I had a short circuit and attached a ...
1
vote
2answers
2k views
current in series resistors and voltage drop in parallel resistors
when we have resistors in series, the current through all the resistors is same and the voltage drop (or simply voltage) at each resistor is different.
Question 1: it is fine that voltage drop ...
0
votes
1answer
177 views
What does a positive gradient on a graph of V plotted against I mean in terms of EMF and internal resistance?
According to the equation $V = E-Ir$, the gradient of a graph of $V$ against $I$ should be $-r$ (internal resistance) and the Y intercept should be the EMF. Am I right?
In an experiment I used a ...
3
votes
3answers
4k views
Why do birds, sitting on electric wires, not get shocked?
If we would touch electric wires, we would get a shock, even if we are not touching ground (so that no connection is complete form wire to ground through us). I always see that birds sit on electric ...
0
votes
1answer
336 views
Calculate the UPS Capacity in amp-hours [closed]
I am trying to find out the UPS capacity in amp-hours for my HP UPS system.
I've already done some calculations based on the UPS information from the HP Power Manager software.
Bellow are my ...
1
vote
0answers
59 views
Effect of Current on spring
When Current passes thru a spring , some books mention that it gets compressed.
However, I think due to the heating effect of current, molecules will increase kinetic energy and the spring should get ...
1
vote
3answers
2k views
Finding current using EMF & internal resistance
What exactly is the difference between internal resistance and resistance?
This came up in the context of a homework problem I have been given:
The circuit shown in the figure contains two ...
1
vote
2answers
397 views
An Ideal Transformer
In a transformer assumed to be transformer, power in the primary is equal to power in the secondary. So in a sense, the power in the secondary is 'fixed'. Output voltage in the secondary is also fixed ...
0
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1answer
175 views
Capacitance and Light Bulb And Dielectric Slab [closed]
An electric lamp having coil of negligible inductance connected in series with a
capacitor and an AC source is glowing with certain brightness. How does the
brightness of the lamp change on reducing ...
3
votes
6answers
3k views
What causes an electric shock - Current or Voltage?
Though voltage and current are two interdependent physical quantity, I would like to know what gives more "shock" to a person - Voltage or Current? In simple words, will it cause more "electric - ...
0
votes
1answer
85 views
Why is the anode (+) in a device that consumes power & (-) in one that provides power?
I was trying to figure out the flow of electrons in a battery connected to a circuit. Conventionally, current is from the (+) terminal to the (-) terminal of the battery. Realistically it flows the ...
1
vote
2answers
641 views
Does the 'mAh' rating of a battery have something to do with its power?
I'm curious about the 'mAh' of a battery: how can this impact the power of the battery?
I've done some research on the internet, and most of the articles I found explain about the 'amount of charge ...
3
votes
2answers
385 views
How do electrons know that?
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?
0
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1answer
100 views
How to measure electrical resistance?
Is it possible to theoretically measure the resistance of passing of electrical current through liquid electrolyte (distilled water + NaOH) ?
0
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0answers
141 views
How much current needed to cancel Earth's magnetic field [closed]
It can be shown the magnetic field in a long narrow tube that is 5 meters is uniform and given by
$$B=1.26 \times 10^{-6} N I$$
where N is number of wire loops/meter. Assuming the solenoid is aligned ...
2
votes
3answers
2k views
How does electricity flow in conductor when potential difference is applied?
Electrons move from higher potential to lower potential. When a conductor is connected to battery, electron move from negative terminal to positive terminal.
But the battery itself forms a Electric ...
2
votes
0answers
79 views
How much current would be generated by polarity reversal of Earth's magnetic field?
Continuing from my previous question Is reversal of magnetic polarity in a planet an instantaneous occurence?
A change in magnetic flux is expected to generate an EMF.
In the case where the ...
1
vote
2answers
296 views
Calculate power $P=V \times I$
I have an adapter which mentions like this...
Input: 100-240V~1.8A
50-60hZ
So how much power does it really consume?
I just knew ...
0
votes
1answer
255 views
Improvement Of Soft Iron And Steel As Magnets
I am given to know that soft iron is used as temporary electromagnet since it has high permeability i.e. the ability to align its domains corresponding to the electric field around it, however has a ...
1
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1answer
143 views
Residual Resistivity in alloys and metals
Residual Resistivity
I saw that the graph of resistivity to temperature of alloys like nichrome is like so
Meaning that even at 0 K it has some resistivity just like copper :
I read some where ...
1
vote
1answer
985 views
Which derivation of drift velocity is correct?
In the derivation of drift velocity I have seen two variations and want to know which one's correct.
$s=ut+\frac{at^2}{2}$
Assume that the drift velocity of any electron in any conductor is :
...
6
votes
2answers
347 views
Voltage and current of positive lightning
For a physics issues investigation I chose to investigate what effects lightning could have on an aeroplane while in flight if it was struck and then go on to discuss some possible implications of ...
1
vote
2answers
171 views
Fundamentality of voltage to current
From Ohm's Law :
Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points.
I would like to know if ...
4
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6answers
5k views
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?
2
votes
1answer
527 views
How does a voltage independent current source work?
So I'm having some trouble understanding what a voltage independent current source is. How can you have a current without a voltage. as I understand it voltage or EMF is the force that drives the ...
1
vote
1answer
2k views
Current against the inverse of resistance graph, $I = V/R +c$
If I have a plot of current ($y$ axis) against 1/Resistance ($x$ axis).
The circuit it is measured from is a simply 2 resistors connected in parallel to battery, where the potential across the ...
5
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2answers
1k views
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 ...
11
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4answers
2k 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 ...
4
votes
6answers
6k views
Difference between current and voltage sources
I am confused about the current and voltage. My intuitive example would be that of a pipe of say water. The diameter of the pipe determines the amount of water flowing per second but the pressure is ...
