What is Electomagnetism: Definition and 27 Discussions

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  1. Sh_lm

    Modelling a metal detector using eddy currents from Non-Destructive Testing

    I'm trying to model a metal detector for my internship project. The system consist of one coil energised with an oscillator to create a magnetic field. The principle of the detection is by measuring the change in the coil impedance. with biot et savart law the magnetic field create by the...
  2. K

    Force Between 2 Coaxial Current-Carrying Loops

    I have attempted to solve it as follows: Using the Biot-Savart law, I found the flux density at the centre of the smaller coil due to the bigger coil as: $$\frac{\mu_0 I b^2 N_2}{2(a^2 + b^2)^{1.5}}$$ where a is the distance to the coil (10cm), N2 is the number of loops in the larger coil (50)...
  3. C

    Force on rectangular loop by a current in a long straight wire

    Hi, I am struggling to get the right answer for this question. My first thought was that I should consider to what direction does each segment of wire have a force towards. I found the direction to be in the following (see red arrows): My past attempt was: Floop = IlooplloopBwire Since Bwire...
  4. user2539

    Magnetic equivalent circuit for a UU-core inductor

    Hello, I am trying to develop a magnetic equivalent circuit for a UU-core inductor with two parallel bus bars in the middle of the slot. I am not sure as to how to model the MMF in such problem. The logical way in my mind is to have two current sources to represent the fields of each bus bar...
  5. A

    B How can scalars like voltage, impedance, etc. be added like vectors?

    So we learnt about the different types of circuits and their behaviour when connected to an alternating current source. (DC was treated as an AC with 0 frequency and/or infinte time period). For purely inductive and purely capacitive circuits we were shown the derivation and why things are the...
  6. A

    Importance/Use of Gauss' Law and Ampere's Circuital Law

    So the question is like I mentioned. I know how to use GL and ACL in place of CL and BSL. I also know that they make the calculations simpler. The problem is whenever GL and ACL are used in place of CL or BSL, they are used in the following way: Gauss Law:$$\int{ E...
  7. D

    B When a charge moves with respect to a second charge, does the electric field change?

    So consider you have a point charge ##q_1## which is somehow fixed in space so it won't move if a force is applied to it. Then at some distance away you have another point charge ##q_2##, where ##q_1## and ##q_2## are of comparable magnitude (so, one is not insignificant compared to the other)...
  8. S

    I Question about Coloumb's law notation and math in two different textbooks

    I am currently taking Electricity and Magnetism I for Graduate school and we are of course using Jackson Classical Electrodynamics 3e. I am used to Griffiths from undergrad and intro physics in that they describe it: But Jackson modifies the notation to include a cube of the magnitude in the...
  9. EleSuki

    B Frequency of EM Waves from Monitor for Black/White & Color Images

    I am using an old monitor (MITSUBISHI RDT27IWLM). The power consumption changes when the screen is white or black, but does the frequency of the weak electromagnetic waves emitted from the monitor change? Or is the frequency the same, only the output is stronger/weaker?
  10. sal1854

    I Direction of motion of particles with total spin under magnetic field

    According to Chapter 8 of Griffiths' book Introduction to Electrodynamics, the magnetization force that acts on a magnetic dipole is $$F_M=\nabla (m \cdot B)$$, where ##m## is the magnetic moment and ##B## is the magnetic field. For a paramagnetic or diamagnetic particle...
  11. V

    I Electric field of a moving charge that's abruptly stopped

    Hello everyone, This is in reference to fig 5.19 (screen shot attached - please read the paragraph which says "Figure 5.19 shows the..."). I don't get why the field outside of the sphere of radius ct acts as though the particle would have continued its motion. Author's words : "The field...
  12. V

    Trying to understand electromagnetism

    Hi! I'm trying to understand electromagnetism. Please help me. Say we have an electron start moving a sine wave like pattern along z axis with amplitude of 1m up and down with frequency equal to 100Mhz. I want to determine an electric and magnetic field vectors in any arbitrary point in any...
  13. M

    Helix Angle or Pitch Angle for this Solenoid carring Current?

    I honestly have such a dumb question- it says “a pitch angle” but cannot find that in relation to a helix. It is not defined in the textbook. Looking on google I found a helix angle, but is that different than the pitch angle? Can anyone draw me a picture of where the pitch angle is? I assumed...
  14. wykk

    A uniformly charged rotating sphere does not radiate, why not?

    The problem says I have a spherically symmetric spinning constant charge distribution of charge Q and angular momentum w; I saw two possible explanations but none of them has made me realize why it is zero, one mentions thata constant w somehow implies a constant E which would mean there is no B...
  15. Johan L

    EM re-radiation from a metal object (antennas)

    Consider the following situation. Two identical monopole antennas are placed in a field with distance d. One of them is used to receive signals and the other is disconnected and can therefor be considered to be just a metal rod (my guess). A plane wave of a single frequency is coming from a...
  16. V

    Time derivative jump of the electric/magnetic field

    So I just wanted to see if anyone could offer some suggestions. So in my mind this seems impossible, in the case of electric field a jump in time derivative of that field would indicated in my mind that electric charge was either introduced or removed from the system instantaneously which would...
  17. A

    Is the Lorentz magnetic force verified?

    Can someone provide me with some original experiments conducted which verified the Lorentz magnetic force : F = q(v X B). Google does not give me any links except to explanations of the Lorentz force law.
  18. K

    A challenging capacitor problem

    1. Two identical flat plate capacitors are inserted in each other. First, none of the plates was charged, but then they have been connected to sources of current, keeping the constant voltage ## V_1 ## and ##V_2 ##. Find the potential difference between inner plates, which are kept at the...
  19. BillTre

    Spiders Flying by Electrical Charge

    Some spiders are known to fly on the breezes by extruding silk strands (like web material) from their abdomen. This is commonly thought to be caught in the wind and carry them away. This would explain the occasional spider you might see drifting by when you are outside. Many (including that...
  20. R

    I Understanding Gauss's Law and Special Cases in Maxwell's Equations

    I have an issue with Gauss's Law when it is considered one equation of Maxwell's complete system of equations. I don't have an issue with it when it is a standalone equation, but when it is one of several equations put together to form a complete system of equations, there is an issue. How is...
  21. U

    Studying Electrodynamics and Classical Mechanics?

    I am preparing for an exam which requires me to solve problems in electrodynamics and electrostatics problems along with classical mechanics and geometrical optics problems. The concern is that I do not have electrodynamics in my course in school so I have to study it completely on my own. I...
  22. M

    Why do I have to use integration and components?

    Homework Statement in the picture. Homework Equations F=ILcrossB Along with the original question, the other picture contains the solution with different numbers. I was just wondering why when finding the force on the wire instead of making dl= R*dtheta and going through the integration and...
  23. V

    Vector potential of a plate with a uniform, time-harmonic current density

    Hi all, i tried to do this question but got stuck on the last point . Can anyone help me please? The general form of vector potential: I got the answer for A1 vector potential but don't know what assumptions i need to get the expression for the A2. Does anyone know how one can derive it...
  24. S

    Physics 12 Help- Electomagnetism and Torque

    Homework Statement If you were given this question: http://img40.imageshack.us/img40/975/picture7we.png how would you go about solving it? Homework Equations I found a formula that makes this question seem a lot easier. Torque = NIAB. however, this formula is not on the formula...
  25. Y

    Solve Electromagnetism: Gold Nugget Net Charge Problem

    1. Suppose a 1.0-g nugget of pure gold has zero net charge. What would be its net charge after it has 1.0% of its electrons removed? please help! i don't know what to do