# electricity

1. ### B Retarded and advanced potentials

"of the two types of solutions which the Maxwell equations yield for the wave equation, the retarded and advanced potentials, only the retarded field seems to have a physical meaning," let's start please with basic (and detailed as possible for the knowledgable layman! p.s-which equation is...
2. ### I What are the potential effects on electricity due to Earth's magnetic field reversal?

What is/are the potential or theoretical effect on electricity due to reversal of planetary magnetic field? Would circuitry continue to function or would knowledge and understanding need re-evaluating as a result of a reversal of our magnetic field on planet Earth? Note: this is not a homework...
3. ### I Efficiency of computers vs. brains

Hi, I’m an undergraduate student interested in cognitive processes. I’m about to ask a very interdisciplinary question, and so hopefully I can find a physicists that can take on the challenge. What is the fundamental reason behind why modern electronic computers (transistor computers) are...
4. ### Inserting a dielectric material between two plates of a capacitor

1. new capacity: $C = K\cdot C_{0}$. 2. initial potential energy: $U_{i} = \frac 1 2 \cdot C_{0}V_{0}^2$. 3. final potential energy: $U_{f} = \frac 1 2 \cdot KC_{0}V_{0}^2$. 4. total work done: $W_{tot} =\Delta U = U_{f} - U_{i} = \frac 1 2 \cdot (K-1)C_{0}V_{0}^2 > 0$. 5. also total...
5. ### Joule heating effect - qualitative explanation

Hi, I understand mathematically why using low resistance results in a greater heating effect. Could someone give an intuitive and microscopic picture of why the current contributes more to a greater power dissipation by the resistor rather than the resistance contribution to the power...
6. ### B Request for historical background on the concept of voltage

Hi all. I'll get to the point. I've been interested in electricity since I was in college. Concepts such as current and resistance seemed easy to grasp for me but voltage remains a little bit obscure. It's thanks to this forum (specially forum members Jim Hardy r.i.p and SophieCentaur, sorry if...
7. ### I RC charging - intuition behind equal dissipated energies?

Assume that a resistor R charges a capacitor C, whose other terminal is connected to the ground. The charge at time t = 0 is assumed to be null and the supply voltage is equal to V. We have, as is well known, $i = \frac{V}{R} e^{-\frac{t}{RC}}$. Integrating $\frac{i^2}{R}$ between t = 0 and...
8. ### Calculate the total resistance by integration using the conductivity equation

(i) Dividing the rod into thicknesses of dx we get discs of area A with lengths=dx so using (****) we have the resistance of a typical disc (between point x' and x'+dx) as: (1) $R(x'dx)=\frac{dx}{g(x)A}$ (ii) Using (1) and (*) and the integrating from a to b of the entire rod we get...
9. ### Can constant electrical current heat water?

Hi, I'm trying to make a realistic scene, in which water is kept under constant electrical charge. If the power is around 75 milliamps, and it's in a stream about twenty feet across by ten feet deep, would this affect water temperature? Thanks!
10. ### LDR circuit electricity question

So far what i figured out is that R2 and R3 are in parallel, R1 and LDR in parallel. And these two parallel circuits are parallel to each other ( tell me if im wrong) The voltmeter has to read 0 but im not sure how i can achieve that. Is there a rule where when the resistance of each side is...
11. ### AC Electricity Generation and Transmission over a Single Wire?

I'm a bit confused as to why can't you transmit AC current over a single wire. For instance, say you have an AC generator which induces potential difference at different points of the wire and thus, creating current. Downstream, the wire can be split and applied to a load. When the wire is...
12. ### I Electricity: Is it a longitudinal wave?

I am a high school teacher and we were discussing waves and electricity in class today. One of my students asked me if electricity is a longitudinal wave or not and I had no idea how to answer. So, I realize that electric fields are what drive electrons to move through conducting wires, but...
13. ### How easily can a high amperage electric fence be shorted out?

Researching for a Scifi novel that depends heavily upon electricity...something I don't know much about! Any input would be appreciated! My situation: Somebody is trying to sneak through a high powered electric fence. Is it at all feasible to short out the fence somehow -- like, connecting it...
14. ### Engineering Help me finding the current in here please (Circuit analysis)

Hi! I've been struggling with this. Original exercise here: Find the value of Iy when R=0. And the value of Vx when R is infinite. For the first part of the question I did this since R=0: I've tried to solve this circuit and I get that Iy and I5 are 0 A, and this can't be possible since Iy...
15. ### Electrical generation from used water in my home

Hi everyone. I was just out in my back garden and was watching the water from someone's shower pour down the pipe and out into a drain. I was thinking if all of the used water from my house just goes down a drain then why not try make use of it. If the water system continues after use and takes...
16. ### I need to calculate the equivalent resistance

1. Homework Statement The circuit is the one in "Fig.4" I need to calculate equivalent resistance between A and B. This is what I've tried: I think that the first resistor is shorted by that wire connected between A and E. Their answer looks like this, in fig 2.2.1. I'm not sure if their...
17. ### Potential across a conducting sphere surrounded by an insulator

1. Homework Statement A conducting sphere has a radius of 2.25 m and carries a positive surplus charge of 35.0 mC. A protective layer of barium titanate is applied to the surface of the sphere to make it safe for laboratory workers nearby. Safety considerations dictate that the potential...
18. ### Writing: Input Wanted Water and Electricity...

I'm working on a Scifi novel, and trying to make it somewhat...scientific! Any advice is appreciated. Here's my question: I'd like to write about a situation where a body of water is purposefully kept under electric charge for years on end. This body of water would vary in size and depth, but...
19. ### Hello, Smart People!

I was told to introduce myself before asking a question. So, I'm a writer -- and that's why I joined this forum. My current project is Scifi -- with more "sci" than "fi" at certain points, haha! I AM NOT very scientific, so I'm hoping I can get smart people to answer some questions now and then...
20. ### B Electric arc: How to calculate the required voltage for a light bow?

<Moderator's note: Moved from a homework forum.> Calculate the required voltage to produce a electric arc between 2 iron nails (distance: 3cm). I´ve read in the internet that you need 1 kV per mm. But how can I calculate this value, that I need 1kV per 1mm?
21. ### B The Gain of the Inverting Amplifier and Virtual Earth...

This is an inverting amplifier incorporating an ideal op-amp with infinite open loop gain. I have a simple question concerning the derivation of its gain (-R2/R1). The point I circled is at 0V (Virtual Earth) but then, if V+=V-, Shouldn't Vout=0 regardless of what R2 and R1 are?? What's wrong in...
22. ### I Electrostatic generator

Hi all Interested in making an electrostatic generator, anyone have experience of building one and also what type would be the most efficient build induction or friction based? Lots of info on the net regarding the principles but and good books for this or websites? Also how best to...
23. ### B Why we use the conventional direction for current flowing?

I often get confused that why we have to use the ancient idea for the direction of current flowing.I have come to know a very weak reason for it.It is said that when current was first discovered,it was assumed that the current flows from the positive region to the negative region(using the idea...
24. ### I Power waste (conceptual doubt)

I'm currently in a undergrad level course of eletromagnetism and my professor found it useful to remember quickly of some relationships that we see in high scool, among them power waste. I got the formulas, since they're simple and are direct derivated from the definitions of electric current...
25. ### Combination Circuit Help (pic)

Could somebody help me out with this combination circuit? The answer that I get is 62K but that is not one of the answers. At first, I thought the 10kohm and 20kohm wherein series and the other side as well. Then I thought they are all in parallel because of the different current flow they all...
26. ### A charged cork ball is suspended on a light string in the presence of a uniform electric field

1. Homework Statement A charged cork ball is suspended on a light string in the presence of a uniform electric field. E=(3×10^5 N/C)i+(5×10^5 N/C)j. The ball is in equilibrium in the field. Find the charge on the ball. The acceleration due to gravity is 9.8 m/s2 . The mass of the ball is 0.7g...
27. ### I Electrostatics from particle laden air

Is it possible to generate static electricity from air flow containing particles example smoke or dust flow, or does anyone know of experiments such as the kelvin water dropper converted to generate static from air flow ? Thanks
28. ### Why don't voltages add up numerically in an LCR AC circuit?

The attempt at a solution (Assuming the components are in series of this order: resistor, inductor, capacitor So I know that the phases are not in sync, that as the voltage oscillates the voltage across each component in the circuit is different. At the peak voltage aka peak current the voltage...
29. ### I Spatial dependence of induced Electric field

The Faraday's law and Lenz's law together give you, $$\xi = -\frac{\partial\phi_B}{\phi t}$$ or put another way,$$\vec{\nabla} \times \vec{E} = -\frac{\partial \vec{B}}{\partial t}$$. My question, I am just asking to make sure, the spatial dependence of $\vec \nabla \times \vec E$ will be the...
30. ### I Why does Fleming's right hand rule apply for induced current

I know that the right hand rule applies for induced currents, and the left hand rule is for motors, but why? It doesn't seem to connect with any other physics laws and is very counter-intuitive that the current will flow in one direction rather than the opposite direction if both are...