The study of the presence and flow of electric charge. Charges, currents, fields, potentials.

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Can the lightning be captured and used as power source?

I would like to update my knowledge in this area, that is really out-of-dated and stopped somewhere like ten years ago. I asked the very same question on my physics lecture at my studies and got the ...
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4answers
1k views

Parallel or series connection?

Are C1, C2 and C3 connected in parallel, or C2, C3 in parallel and C1 in series with C23? Btw it appeared as a question in the basic physics Albanian A-levels yesterday. You had to find the ...
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2answers
1k views

Simulator for electrostatics [closed]

I am searching for a tool that visualizes the electric field/potential for simple electrostatic configurations like conducting/polarized sphere in an uniform electric field conducting/polarized ...
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1answer
485 views

confusion about finite line charge

My physics knowledge is (sadly) very infinitesimal and I have a question about a calculation which I think is wrong, but want to be sure. I tried to calculate the potential of a finite line charge. ...
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1answer
690 views

Light bulbs with voltage source or current source

When we connect 2 light bulbs to a voltage source in parallel, the equivalent Resistance of the bulbs is R/2 (1/Req = 1/R + 1/R). If we connect these lights in parallel we have Req = 2R; I= V/Req is ...
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1answer
656 views

Pull up and Pull down register

Currently I am working with Pull up and pull down registers and trying to understand what does it mean? But could not able to understand. I searched in Wikipedia ...
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1answer
134 views

Do you think it’s possible to make a power plant of the described kind?

We are working on a science project and try to engineer a power plant of a new kind. It is called Air HES (air hydroelectric station). The idea is described on our website. Do you think it is ...
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3answers
8k views

Two 60W-lightbulbs are connected on 220 V AC-voltage - how much electric power is spent by each lightbulb? [closed]

Two 60W-lightbulbs are connected on 220 V AC-voltage - how much electric power is spent by each lightbulb? There are two scenarios: In one, these two lighbulbs are connected serially, and in the ...
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2answers
470 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 ...
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0answers
2k views

Question on Shockley's diode equation

We owe a debt to Bell labs with Shockley, Bardeen and Brattain for inventing the semiconductor. All have now passed on. I remember seeing my first transistor radio in the early 60's. Shockley ...
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1answer
176 views

Does recharging a battery at a lower temperature lower its internal resistance?

Does temperature affect the internal resistance of batteries? And does charging a "frozen" battery allow it to charge faster than a warm or room temperature battery?
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0answers
67 views

Piezoelectrical effect in a pendulum

How can I compute the piezo-electrical effect of a pendulum of frequency $f$ and amplitude $R$? What constants of the material will enter the computation? The material in question is an electrode on ...
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2answers
32k views

Has any permanent magnet motor been proven to run?

I have read lots of articles about permanent magnet motors, some of which claim the possibility and other which refute it. Is it possible to have a permanent magnet motor that runs on the magnetic ...
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2answers
189 views

Does using batteries in a series raise the overall Wh's of the batteries used? Why/Why Not?

If one has 2 batteries of 6 Volts each with 500 mAh each, then separately the batteries should provide 6 Volts * 500 mAh = 3 Wh each or 6 Wh total. However would it be the case that if someone where ...
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1answer
536 views

Emf Of a Cell in a common circuit

My questions will be based on the above figure. The Emf Source V1 and R1 Together form a cell(R1 is internal resistance) R2 Represents the entire load on the source VoltMeter My teacher told ...
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1answer
494 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 ...
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2answers
288 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 ...
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2answers
6k views

Why connect cells in parallel?

Say there is a circuit with two 1.5V cells, and a 100 ohm resistor. If you connect two cells in series, then the total emf is 3V. And the current will be 3/100 = 0.03 A. (Using V = IR): If you have ...
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3answers
20k views

Would you die if you put your hands on a powerline?

You know how birds perch on powerlines without getting electrocuted? What if by some chance that I find myself falling and I grab on one of them? Let's say both of my hands are on the same line, would ...
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3answers
2k views

Why does the potential drop across a battery and resistor equal the emf of the battery?

In this diagram you can see the potential difference across the battery and resistor is the same as the pd created by the battery (the battery and resistor are representing a battery with internal ...
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3answers
194 views

Resistance of superconducting wire in parrallel with standard wire

The formula for parrallel resistors is $\frac{1}{R_T} = \frac{1}{R_1} + \frac{1}{R_2}$ But how can you use this formula when one of the branches is a superconductor, eg: Where the red resistor ...
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5answers
651 views

This sentence makes no sense, electrostatics and electrons moving in a conductor - current

I highlighted the part where the confusion is. The sentence said that the potential difference is 0, yet it then immediately talks about how electrons can have motion. What are they trying to ...
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1answer
1k views

Can lightning be used to solve NP-complete problems?

I'm a MS/BS computer science guy who is wondering about why lightning can't (or can?) be used to solve NP complete problems efficiently, but I don't understand the physics behind lightning, so I'm ...
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2answers
1k views

Schematic design of the apparatus (photoelectric effect)

I think I understand the basic idea of photoelectric effect but there are two things in the schematic diagram of the apparatus for the investigation of the photoelectric effect which I do not ...
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1answer
9k views

Why does it spark when I push a plug in the electrical socket?

When I slowly push a plug into the electrical socket I can often see sparks. Can anybody explain why? Can this be possibly harmful for the devices I plug in?
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6answers
25k 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?
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1answer
1k 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 ...
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2answers
864 views

is the voltage drop of a battery that is being short circuited the same as the battery's advertised voltige

So I know this is a pretty fundamental question, but I'll ask it any way. lets say you have a 12V battery, and the positive is connected to the negative directly by a wire with negligible ...
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1answer
385 views

Equipotential Contour mapping and making it 3D [closed]

I have seen Contour diagrams for Equipotentials . That are drawn like so: I also saw One image for these contours that was in 3D (Negative Point Charge) : I was Wondering If there's any ...
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1answer
218 views

Toroid with variable current and Ampere's Law

Say you have a current $I(t)$ (notice the time dependence) flowing through a Toroid with $N$ total loops and all the usual approximations: $(b-a) \ll r,\; B=0$ outside. You are asked to calculate ...
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0answers
20 views

I want to charge 48V 108Ah battery from 48V 80Watt solar panel. Can anyone write that how much time will take this battery to fully charge? [duplicate]

Possible Duplicate: Charging 12V 150Ah battery I want to charge 48V 108Ah battery from 48V 80 Watt solar panel. Can anyone write that how much time will take this battery to fully charge?
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3answers
423 views

Can I get anions by touching the negative electrode of a battery? [closed]

It is said that anions are good for health. Instead of using an anion generator, can I get anions by touching the negative electrode of a battery?
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3answers
1k views

How does energy depend on frequency in an alternating current circuit?

In what relation is the energy input in an alternating current circuit to its frequency? I'd guess I have to compute something like $$E=\int P(\omega,t) dt=\int U(\omega,t) I(\omega,t) dt, $$ but ...
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2answers
4k views

Can a camera flash light near high voltage wires create medium to pass electricity?

I found a story of a boy who took a picture with flash light near 40,000 voltage lines. When it flashed, current came to his camera (as a spark may be) and passed through his body making him dead. Is ...
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3answers
3k views

Is it possible to mathematically derive the formula for resistance?

Resistance is given by $\rho L/A$, where $\rho$ is the material constant, $L$ is the length, and $A$ is the area. Is there any way that this can be derived mathematically, or is the only way ...
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1answer
6k views

What defines the brightness of a bulb?

So I have a question. There are three identical bulbs, 2 of them are connected in parallel and the third is basically in series, on the same circuit. If the one of the lamps in parallel breaks, what ...
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7answers
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Why does a glass rod when rubbed with silk cloth aquire positive charge and not negative charge?

I have read many times in the topic of induction that a glass rod when rubbed against a silk cloth acquires a positive charge. Why does it acquire positive charge only, and not negative charge? It ...
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5answers
4k views

Magnetic flying engine [closed]

I invented a flying engine moving entirely by magnetic forces (such as the force related with magnetic field of the Earth). See http://porton.wordpress.com/2011/12/23/magnetic-vehicle/ The question ...
3
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1answer
200 views

Theory of Space Charge in a Planar Diode

A planar diode in a vacuum bulb can support current in only one direction. To even get current flowing, you have to heat up the cathode filament to excite the electrons. However, once current is ...
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1answer
351 views

What is lambda R in Richardson's Law?

I've got to calculate the thermionic emission through a diode, so I need to use Richardson's Law. However, one thing's got me confused - according to the Wikipedia page: $$J = A_GT^2e^\frac{-W}{kt}$$ ...
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1answer
6k views

How to know what materials are good conductors of electricity?

I'm not asking a question like "Is the wood conductive?". No. I'm asking what properties do they have to have to be good conductors. Theoretically I mean. Thanks.
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1answer
347 views

Question Based On Direct And Alternating Current

A Wikipedia article on Power engineering reads, Most refrigerators, air conditioners, pumps and industrial machinery use AC power whereas most computers and digital equipment use DC power. As ...
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3answers
1k views

Why do charges enter the capacitor in the first place?

I have been studying Capacitors for the past year now and the one thing I don't understand is how a charge is stored on the capacitor. Essentially, a circuit with a capacitor is an incomplete circuit ...
2
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1answer
918 views

How is contact resistivity defined for a Schottky contact, or the Schottky barrier height for an ohmic contact?

Based on the transfer length method (TLM), one can accurately calculate the contact resistivity for an ohmic contact, by evaluating the absolute resistance measured through the test structure and ...
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1answer
1k views

Definition of Free Electrons and Mobile Charges?

Could someone please give me a good definition of the following electric terms? Despite what searching I have done, I have not come across a definition that I have found clear for me to understand: ...
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4answers
5k views

Resistor circuit that isn't parallel or series

What's the equivalent resistance in this circuit (between points A and B)?
2
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2answers
4k views

Microwaves vs Gas or Electric Coil heating of a water boiler in a typical household

Wouldn't it be more energy efficient and or safe to use microwaves to heat our home's water boiler instead of using dangerous gas or hot electric coils that could catch other things on fire? I'm kinda ...
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5answers
1k views

Can someone explain the science behind MIT's 230% efficient LEDs?

I was reading Gizmodo the other day and I didn't quite understand the Physics behind this. Could anybody shed some light on how this effect actually works?
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2answers
1k views

General integral to find resistance

My question is: is there a simple and truly general equation for the resistance between two electrical equipotential surfaces?. Obviously, if so, what is it, and if not, why? It would be very ...
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1answer
2k views

Why does electrical current start to flow?

What happens microscopically when an electrical current starts to flow? I'd like to understand microscopically what happens in detail when electrons start moving (quasi-classically). Electrons can ...