# What is Electrcity: Definition and 92 Discussions

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1. ### Current through a circuit when the key is open

The equivalent resistance of the parallel combination is 2.4 ohm. This implies that if the key is closed the total resistance of the circuit = R + r = 2.4 + 0.6 = 3 ohm However, if the key is open, no current flows through the circuit and thus, by Ohm's law (R = V/I), as I tends to 0, R tends...
2. ### Classical Looking for a textbook that uses the electromagnetic wave view of electric current

So I watched a couple of videos on Youtube with the titles 'How Electricity Actually Works' and 'The Big Misconception About Electricity' ( and ). The main message being that while the view of current being the flow of electrons might be useful practically, it's not an accurate representation...
3. ### I Can Conducting Current Through a Bar Magnet Cause Movement?

Following the Picture below, If I Conduct current through Permanent magnet Bar and hold the battery still. Will the magnet move in any direction ? Thank you.
4. ### How does the presence of a cube resistor affect current flow in a circuit?

I would think that it is 2 A (6/3 because there are three wires the current can go to), but this does not seem to be correct.
5. ### Is it possible to build a low-voltage Thompson jumping ring apparatus?

Hi all, I'm attempting to build a jumping ring apparatus (a core of iron with the bottom wrapped with wiring like an electromagnet, so that when a metal ring is placed on top of the coil and a current is run through the coil, the ring jumps up into the air). Looking on the internet, I'm seeing a...
6. ### Force between 2 point charges in VECTOR format (x i + y j + z k)

I tried using the distance between r2 and r1 and plugging them into the equation for i, j, k. >> So for the force in the x direction it was k*(4E-6*4E-6)/(4-9)^2. The answer I got was wrong according to webassign. Can someone please tell me what I am missing?
7. ### B To confirm if I am correct about the role of voltage in a circuit

i just finished some basic concepts about electricity and wanted to confirm if my deduction/understanding is correct: in a simple circuit of let's say a battery and lamp,motor,resistor, the difference between potential of two ends of battery(voltage) say how much potential energy per charge has...
8. ### Voltage detection in electrical cables

Hello guys! I am a student who currently works on a project based on electrical detection and voltage measurement in electrical cables remotly. So in order to accomplish my work, I'm seeki ng for new ways to detect voltage. I already have some ideas such as using magnetic fields or measuring...

Question

11. ### Cases when Ampere's circuital law fails to hold

Well, I guess that is pretty much my question.
12. ### I Exploring Lenz's Law: Magnetic Flux and Induced Currents

I've attached an illustration of my set up.
13. ### Help with Circuit Nodal Analysis

Summary: Perform nodal analysis on a circuit to find voltages. For a laboratory I am trying to find the nodal voltages for a circuit we built using hand calculations. I have the answer as we ran the simulation which shows all the nodal voltages, however my nodal analysis seems to be wrong as I...
14. ### Capacitance and induced charge of a spherical Capacitor + dielectric

I) For the first part I used: ##V = - \int E ds = \int_a^c \frac{1}{4\pi\epsilon_0} Q /r^2 dr+ \int_c^{c+d} \frac{1}{k} \frac{1}{4\pi\epsilon_0} Q /r^2 dr + \int_{c+d}^b \frac{1}{4\pi\epsilon_0} Q /r^2 dr ## And by using ##C = Q/V## We get an answer which is somehow large for writing here...
15. ### Calculating the charge of two concentric conductive spheres

Homework Statement The solution to this problem is B, and I was able to get the answer by calculating the total potential at ##r = 2a##, however, what I don't seem to understand is why must the voltage be calculated at ##r=2a## but not ##r=3a##. Homework Equations ##V(r) = - \int_a^b E(r)...
16. ### Interesting Magnetic Field Induction Problem

Homework Statement Suppose we have an isolated, long, narrow straight wire with low electrical resistivity. A constant current ##I## is sent through this wire. We know that if an electron is sent on a path which is perpendicular to the wire, towards it, with an initial speed ##v_0##, and the...
17. ### Electrical Why isn’t this Tesla coil working?

Hello all! I have made a Tesla coil using a proven circuit I found online but what I have made isn’t working here is a picture please help. PS: yes I know it is fairly messy but the specs are as fallows: B50k potentiometer One green 5mm led One 200ohm 1/4 W 5% resistor Primary coil is 8...
18. ### Thevenin's Theorem, Superposition & Norton's Theorem

Homework Statement FIGURE 1 shows a 50 Ω load being fed from two voltage sources via their associated reactances. Determine the current i flowing in the load by: (a) applying Thévenin’s theorem (b) applying the superposition theorem (c) by transforming the two voltage sources and their...
19. ### Shell in a cylindrical capacitor

Homework Statement There is a capacitor (llenght ##L##) made of a conductor (cylinder of radius ##R_1##) and a cylindrical surface (radius ##R_2##). It is charged with a potential ##V_0##, then it is isolated. (There is vacuum between ##R_1## and ##R_2##) Now we insert a cylindrical...
20. ### Why is there a voltage drop in a metal with no electric field present?

Metals are highly effective at screening electric fields. If we place two contacts reasonably far away from each other on a piece of metal and apply a voltage bias, the charge carriers in the section that is far enough from both the contacts should be unaffected by the electric field. Why then...
21. ### Engineering Finding Internal Resistance through Circuit Analysis

Homework Statement Given this following circuit: What is the internal resistance of the meter movement ( R_I). This is part of a project I'm doing and I know the equation that gives you the internal resistance in this circuit. $$R_I = \frac{R_sR_p}{R_s - R_p}$$. However, I have no idea how...
22. ### Electric Field of a Non-Uniformly Charged Sphere | Homework Help

Homework Statement A solid isolated sphere with radius R has a non uniform charge which is given by ρ= Ar², with A a constant and r<R measured from the centre of the sphereHomework Equations (a) Show that the electric field outside the sphere is equal to E = (AR5)/(5ε0r²) (b) Show that the...
23. ### Simple harmonic motion of charged particles

Homework Statement Two identical particles, each having charge +q, are fixed in space and separated by a distance d. A third particle with charge -Q is free to move and lies initially at rest on the perpendicular bisector of the two fixed charges a distance x from the midpoint between the two...
24. ### Flow of charge between two spheres

Lets say I have two spheres of equal dimensions, one charged and one uncharged. Now I connect them with a conducting wire. They will now very quickly reach equal potential. Can it be said that the total charge on each sphere remains almost unchanged?
25. ### Basic question about current in an electric circuit

Let's say we have a basic electric circuit consisting of a battery with some potential difference, and a loop of wire. The wire loop also has some segment with a higher resistance. Now since there is a potential difference, the free electrons will move to make the circuit equipotential. The...
26. ### Electrical current through the Human Body

Hi lads, I couldn't find this info on Google... Are the Heart and Brain the only organs which physiological functions are based on electrical impulses? What happens if we apply electrical current through other organs? Thanks
27. ### B Quantum Field Theory and Electrcity

How work AC/DC current in Quantum Field Theory
28. ### Charge distributions of two infinite parallel plates

Homework Statement Two infinitely large conducting plates with excess charge 2Q and 3Q are placed parallel to one another, and at a small distance from one another. How are the charges 2Q and 3Q distributed? You may assume that infinitely large sheets of charge produce electric fields that are...
29. ### How to find the power consumed by the light bulb

Homework Statement (Is the image read-able now? ) The fig 1 shows the relationship between voltage and current when voltage is applied to a certain light bulb. Next, in fig 2, the bulb is connected in series with a 12-V battery and a 5 ohm resistor. Question : what is the amount of power...
30. ### Two like capacitors in parallel

I'm having a little trouble understanding capacitors in parallel and series. I understand that if there are two capacitors in a circuit with a potential difference Vab then the potential difference across the capacitors is also Vab. Every example I have seen have been for two capacitors with...
31. ### Why do we need to supply air to the cathode of a hydrogen fuel cell

I am trying to understand the working of simple hydrogen fuel cell. We have anode (negative terminal), cathode (positive terminal), catalyst at anode to separate negative and positive ions of hydrogen atoms and electrolyte which allows only positive ions. We will be sending hydrogen fuel at...
32. ### Instantaneous current in stator of 3 phase IM

I am studying induction motors and i have equation for instantaneous value of current flowing in each phases.(please check to image below).I can see that its it the form Im.cosωt But isn't it supposed to be Im.sinωt ?because that's how we find all instantaneous parameters like voltage and...
33. ### Part-Time Student: 300-Level Physics Classes

I'm not if this is the right place for this, so mods can feel free to move this. I'm a part-time student going into my second semester of 300 level physics class. This past semester I oscillated between feeling just fine and questioning whether physics was right for me (usually around test...
34. ### Diagram about potential difference over current

Homework Statement [/B]Homework Equations [/B] I = G * U The Attempt at a Solution [/B] Hello, i know the solution is 5.0 A/V but i don't know if my way of solving this was correct. I rearranged it to G= I/U and solved this equation for all the values in the table and then added them...
35. ### Calculate resistance between terminals 1 and 2, 1 and 4....

Question Calculate resistance between terminals 1 and 2, 1 and 4, 1 and 3, 2 and 4, 3 and 4, and 2 and 3 My attempt of solution: For R between 1 and 2 i done: (R1 + R2) || (R1 +R2 + R3) The problem is: Im not sure how to find which is in series and what's in parallel so I'm confused and I...
36. ### What about the electric field in a circuit with resistors?

Hi. I am having some trouble understanding what is the voltage drop in a system with resistors in series. If there is a difference of electric potential between two points in space, since electric potential is electric potential energy per charge, there is a difference in the electric...
37. ### Basics of radio for a focused transmitter

Hi there! I'm looking to create a small (max 20 foot range) radio transmitter, to direct a focused radio beam at a receiver, for the purpose of remote switching. Ideally, I would like the device to work at a relatively "exotic" frequency, as I would think there is a lot of radio noise where I...
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### What is the Science Enthusiast's Guide to Exploring Different Fields of Study?

Hello everyone! My real name is Ryan, but you can call me Unix (handle I've had since I was a kid). I'm 27 and have always been a huge fan of anything science. I'm formally educated with a BS in Electrical and Computer Engineering and I work as an Engineering Technician for a small electronics...
39. ### Capacitors charged in parallel

Homework Statement Capacitors C1 = 6.97 uF and C2 = 1.54 uF are charged as a parallel combination across a 281 V battery. The capacitors are disconnected from the battery and from each other. They are then connected positive plate to negative plate and negative plate to positive plate. A)...
40. ### What is the apparent difference between the two cases of H=I^2RT and H=(V^2)T/R?

Homework Statement H=I^2RT and H=(V^2)T/R. In one case H is directly proportional to R while in the other it is not where H is the energy consumed. Explain the apparent difference between the two cases Homework Equations None The Attempt at a Solution In the first case electricity is being...
41. ### I Waveguide: get I and II M.eq. from III and IV M.eq.

Consider a waveguide with axis parallel to axis ##z##. Using cartesian coordinates the fields inside the waveguide can be written as Where ##\alpha## is the wavenumber and ##k=\frac{\omega}{c}## . The maxwell equations ##\nabla \times E=-\frac{\partial B}{\partial t}## and ##\nabla \times...
42. ### Could nothing happen when fork in socket

Hi right now I do not have school but I was thinking about what my chemistry teacher said last year. he was telling us about electrons and how they move from negative to positive. he said something along the line of: let's you would put a fork in a wall socket and by chance you first hit the...
43. ### Stargazing Lightning ball - me to analyze this rare video

Hi, Some time ago I was looking for lightning ball videos on youtube. I observed some strange phenomenon recorded on one of the videos. Before a lightning ball is created, some "dark" ball is coming from above and then it immediately changes to the lightning ball which is moving at different...
44. ### Why do conductors have a sea of electrons while insulators don't?

Why is a sea of electrons present in a conductor? I read some where that they absorb a energy at normal temperatures and use it to get free electrons , but then why do they absorb energy while insulators don't??
45. ### What Capacitor Size Is Needed for a Rapid Discharge Application?

This is a pretty simple question, one that there is likely a simple answer to. So, I need to use a capacitor as a rapid dump battery, not a filter or anything. The required current for this application is 1.7 Amps, and only 0.23 volts is necessary. I'm not too sure as to what amount of farads a...
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### Exploring the Wonders of Physics: A High School Student's Journey

Hi guys! I'm a high school student and I love Physics. I hope this site will help me learn and understand a lot of (new) things! :)
47. ### Solutions of wave equation but not Maxwell equations

Maxwell equation in absence of charges and currents are $$\nabla \cdot \bf{E} = 0 \\ \nabla\cdot B=0 \\ \nabla \times E=-\frac{\partial B}{\partial t} \\\nabla \times B=\mu \epsilon \frac{\partial E}{\partial t}$$ Wave equation is \nabla ^2 \bf{E}=\mu \epsilon \frac{\partial^2...
48. ### What is the magnitude & direction of the eletric field?

Homework Statement Two +3.0nC charges are shown in the diagram below which are spaced 10cm apart. What are the strength and direction of the electric field at the position indicated by the dot in the figure (Figure 1) ? What is the electric field in N/C? What is the direction of the electric...
49. ### Electricity: shunt calculation for ammeter

Homework Statement We have an ammeter with 20Ω resistance and a range of 10mA or 0.01A. The different ranges are 3000mA, 300mA, 30mA. Calculate the shunt resistors a, b and c. Homework Equations The Attempt at a Solution Ia = 0.01A ; Ra = 20Ω ; I = 0.03A Ua = Ia ⋅ Ra = 0.01A ⋅ 20Ω =...
50. ### Finding displacement current in an AC capacitor circuit

Homework Statement A capacitor is made of two parallel plates of area A, separation d. It is being charged by an AC source. Show that the displacement current inside the capacitor is the same as the conduction current. Homework Equations Idisp = ε(dΦE/dt) Q = CV C = Aε/d Xc = 1/(2πƒC) Q(t)...