1. ### Could you check this Li-ion charging circuit??

Can secondary cell can be described in circuit simulator?? With other symbols like capacitor. Also I wonder if there's a program that provide secondary cell(like Li-ion battery). Please help me
2. ### B Trying to better understand the physics of electrical earth ground

I'm trying to better understand the physics of how earth ground works. In circuit analysis and other electronic courses they usually present a conceptual picture like below where the earth is viewed as a path that completes a circuit? In this conceptual view, the current travels on the...
3. ### B Does potential drop when a charge flows through a wire w/ 0 resistance?

Let us connect a battery of potential difference V to a wire. There is no resistance. Nothing! Now the battery creates some potential difference and the charges in the conducting wire move due to the Electric field created in the conductor by the battery. So, as the charge moves, its potential...
4. ### B Intuition about electromotive force (EMF)

My understanding of emf Let us consider 2 parallel plates with charges (opp. but equal in magnitude) stored on it. When we connect both the plates from the outer side, the electrons from the lower potential (i.e., negatively charged plate) moves to the higher potential (positively charged plate)...
5. ### Two Charged Balls on Strings

Given the total angles in the x direction, I set up this: (mg/cos(x))*sin(x)-Fe=0 then isolated for x: mgtan(x)=(kq^2)/(2*sin^2x) sin^2(x)*tan(x)=(kq^2)/(2mg) From here I am stuck. How do I go forward when x is contained in two different trig functions on the left?
6. ### How to calculate the efficiency of a switch mode power supply?

I know how to calculate the power output and input by analyzing the current in put and output with multimeters and using the formula P=VI. But P_out is obviously incomparably smaller than P_in so the efficiency would suck this way. Is there a better way to do this??
7. ### B EMF vs Potential difference

Is emf the work done to move a positive charge from LOWER potential to HIGHER potential to maintain the potential difference or else the charges move from higher potential to lower potential and will reach a point where the potential is the same between the two points and the charge will stop...
8. ### Why Can We Consider a Conducting Sphere as a Point Charge When Finding Its Electric Field?

This page claims that "[t]he electric field outside the sphere is given by: ##{E} = {{kQ} \over {r^2}}##, just like a point charge". I would like to know the reason we should treat the sphere as a point charge, even if the charges are uniformly distributed throughout the surface of the...
9. ### Maximum voltage that can be applied to DC circuit with resistors

I see that ##V_{ac}=V_{ab}+V_{bc}##, with ##V_{ab}=I_1R_1=I_2R_2## and ##V_{bc}=I_3R_3##. However, I don't see how to express mathematically the maximum value of ##V_{ac}##. Could someone please help me with this task?
10. ### B Inducing electric current in a wire (a comparison)

Consider the following experiment: from a lacquered copper wire we cut off twenty to thirty pieces of about 10 cm. From them we form a bundle of parallel wires and connect the two ends with one more wire each. The other ends of these two wires are connected to a sensitive analog ammeter. We hold...
11. ### Electrical current question

I assume that because there is a resistance, the polarity of the voltage must be the same as the charge flow, and thus the current, in order for energy to flow in the same direction. For instance, could I use the example of a light bulb (the resistor) plugged into AC lines; we know that if the...
12. ### 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...
13. ### 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...
14. ### 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...
15. ### 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...
16. ### 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...
17. ### 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...
18. ### 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...
19. ### 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...
20. ### 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!
21. ### 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...
22. ### 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...
23. ### 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...
24. ### 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...
25. ### 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...
26. ### 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...
27. ### I need to calculate the equivalent resistance

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...
28. ### Potential across a conducting sphere surrounded by an insulator

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...
29. ### 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...
30. ### 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?