electrcity

  1. T

    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...
  2. Miles123K

    Calculating the charge of two concentric conductive spheres

    1. 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##. 2. Homework Equations ##V(r) = - \int_a^b...
  3. Klaus von Faust

    Interesting Magnetic Field Induction Problem

    1. 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...
  4. A

    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...
  5. Jason-Li

    Thevenin's Theorem, Superposition & Norton's Theorem

    1. 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...
  6. F

    Shell in a cylindrical capacitor

    1. 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...
  7. N

    Voltage drop in a metal

    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...
  8. Safder Aree

    Engineering Finding Internal Resistance through Circuit Analysis

    1. 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...
  9. D

    Electric field question

    1. Homework Statement A solid isolated sphere with radius R has a non uniform charge wich is given by ρ= Ar², with A a constant and r<R measured from the centre of the sphere 2. Homework Equations (a) Show that the electric field outside the sphere is equal to E = (AR5)/(5ε0r²) (b) Show...
  10. A

    Simple harmonic motion of charged particles

    1. 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...
  11. F

    I 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?
  12. F

    I 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...
  13. curiousman

    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
  14. M

    Charge distributions of two infinite parallel plates

    1. 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...
  15. H

    How to find the power consumed by the light bulb

    1. 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...
  16. Z

    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...
  17. srinaath

    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...
  18. rishi kesh

    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 isnt it supposed to be Im.sinωt ?because thats how we find all instantaneous parameters like voltage and...
  19. B

    300 Level 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...
  20. K

    Diagram about potential difference over current

    1. Homework Statement 2. Homework Equations I = G * U 3. The Attempt at a Solution Hello, i know the solution is 5.0 A/V but i dont 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...
  21. H

    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 whats in parallel so I'm confused and I think...
  22. G

    B 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...
  23. OldWorldBlues

    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...
  24. U

    Hello Everyone!

    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...
  25. L

    Capacitors charged in parallel

    1. 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)...
  26. shihab-kol

    Variation of resistance

    1. 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 2. Homework Equations None 3. The Attempt at a Solution In the first case electricity...
  27. C

    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...
  28. N

    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: lets you would put a fork in a wall socket and by chance you first hit the...
  29. Toreno

    Stargazing Lightning ball - please help 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...
  30. shihab-kol

    B Conductors and electrons

    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??
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