# Search results

1. ### Ratio of the Electric field to the Magnetic field

Dear all. I would like to know the general expression of the ratio of the electric field strength E to the magnetic flux density B. I know E/B = c, where c is the speed of light, for a vacuum, but I want to know if this is stil valid for any material where the electric and magnetic fields are...
2. ### How a TFP (Thin Flim Polarizer) works?

Hello. I've been really curious about how TFP (Thin Flim Polarizer) works. I've searched TFP information through the Internet which tells that TFP utilizes Brewster's angle. This explains how the P-polarization transmits TFP with 100 % transmission, but I don't know how the S-polarization is...
3. ### I What is the origin of Van der Waals force?

Hello. Thank you for giving me the explanation. I thought the electron cloud fluctuation occurs even at completely isolated ground state neutral atom. However, you said such a fluctuation occurs only when there is external interaction with it. So, for the isolated atom in the ground state, the...
4. ### I What is the origin of Van der Waals force?

Hello. What I know about the Van der Waals force is that it comes from an instantaneous electronic cloud flucutation of the netural atom. This instantaneous electric dipole of the atom attracts electrons in nearby neutral atoms so other electric dipoles are induced on those atoms. As a result...
5. ### I Is a quasi-static but irreversible process possible?

Thanks you! you and Chestermiller suggest examples of a quasi-static and irreversible process. I've searched the internet and found that the reversible process is quasi-static but its converse is not guaranteed. So, I think the definition of the reversible process given in my book has some hole...
6. ### I Is a quasi-static but irreversible process possible?

Hello. I read the textbook of the thermodynamic and it said the definition of the reversible process as "thermodynamic process which is slow enough so the system state is always infinitesimally close to the thermodynamic equilibrium (quasi-static) during the process. Such a process can always...
7. ### In 3rd step of Carnot cycle, work done on the piston is pdV?

Hm...I got some idea right now. The force –Fpg may not be taken into account in a calculation of the work done on the piston since the origin of this force is the piston itself; the work with –Fpg on the piston may be the work done by the piston itself via the reaction force. It is reminiscent...
8. ### In 3rd step of Carnot cycle, work done on the piston is pdV?

Hello. I really don't want you to be bothered; But..why is -Fpg same to Fpres ? I think they're different entities. Fpres is from the collisions of gas particles on the piston bottom wall, while Fpg is from the state that the piston is pushing the gas downward. Their origins are different, so...
9. ### In 3rd step of Carnot cycle, work done on the piston is pdV?

I appreciate your kind comment:) I would like to simply accept your force balancing on the pistol; your drawing really fits what the thermodynamic textbook try to explain. However, I'm still in trouble. Let's have an extension of your drawing. Here, there is another force on the pistol from...
10. ### Why is entropy a state variable even for irreversible path?

Hello. The entropy S is a state variable or state function as the integral of dS = dQ/T is a path-independent, provided that the path is reversible process path. However, such a path-independency of the integral breaks down when the path includes irreversible process. So, I guess we can only...
11. ### In 3rd step of Carnot cycle, work done on the piston is pdV?

I see. I think I finally got the right answer. Thanks for all of you to guide me along a right track! I attached the summary of what I've learned from your answers and I hope this would helpful for other guys who have similar question.
12. ### In 3rd step of Carnot cycle, work done on the piston is pdV?

Hello. I think you suggested me a way to break through my confusion. Yes, the piston is receiving forces from two things simultaneously; one is the external agency pushing the piston by the force Fe, and another one is the gas pushing the piston due to Newton's 3rd law Fgp (external agency...
13. ### In 3rd step of Carnot cycle, work done on the piston is pdV?

Hello. First, look at the figure describing Carnot's cycle. In 1st step (A → B) and 2nd step (B → C), I fully understand that the work done on the pistol (surrounding) by the gas (system) is dW = pdV where dV = Adl since F = pA is the only force on the pistol from the gas (I assumed there...
14. ### Can a time-varying magnetic field pass a metal sheet?

Hello. I'm sorry but I don't understand your geometry. The circumferential magnetic field around the conductor will induce a voltage on another wire which is in parallel oto the first conductor? This EMF is very different than what I'm used to such as a solenoid coil so I don't get how EMF is...
15. ### Can a time-varying magnetic field pass a metal sheet?

Hello. I'm using CT (Current Transformer) to measure the current flowing on the power line. The frequency of the current is 13.56 MHz. CT appeared to be metal-shielded (This metal case of CT may be grounded when CT is used). CT has a toroidal shape and the power line under the measurement...
16. ### Why is EMF (ElectroMotive Force) equal to a voltage?

Thanks for giving many comments on my question. Especially, I appreciate Jim's consistent comments on me:) The last comments you and Badadag made are something I need to take some time to consume. I'll give anything on this post If I come up with some idea regarding this.
17. ### Why is EMF (ElectroMotive Force) equal to a voltage?

Hello. I've summarized an inductor in my own material which is now uploaded here. On the inductor coil, there is not only EMF-field but also an electrostatic field. In principle, the line integral of a sum of these field along the coil gives a potential difference or voltage on the inductor...
18. ### Why is EMF (ElectroMotive Force) equal to a voltage?

Hello. Let's say a current i(t) flows through an inductor of solenoid type. Time-varying i(t) generates a magnetic field B(t) inside the magnetic core of the inductor. As B(t) is time-varying, EMF, which is the line-integral of the induced electric field E(t) along a coil (which carries i(t))...
19. ### Is there microscopic version of general Ohm's law of V=IZ?

Hello. Resistive Ohm's law is famously known as V = IR. We can derive its microscopic version as being followed. V = El, where E and l are, respectively, an electric field and a resistive load length over which a voltage drop V is developed. I = JS, J and S are a current density and a...
20. ### Identities of fields in Maxwell's equations

Thanks for replying very quick comment! So, E or B-fields in Maxwell's equations are all the same one, in fact. Could you help me a little bit more? I actually want to derive that RHS of \nabla \cdot E = \frac{\rho }{{{\varepsilon _0}}} is zero when E-field here is E-field accompanied with...
21. ### Identities of fields in Maxwell's equations

Hello. I would like to ask one simple question. Do we need to distinguish E-field (Electric field) in Gauss's law from those in Maxwell-Faraday equation and Ampere's circuit law? I firstly thought that E-field in Gauss's law is only for electrostatics so I need to distinguish it from E-field in...
22. ### Some confusion of Faraday's law of induction.

Hello. I really appreciate your help! I've summarized what I've studied for the relation between Faraday's law of induction (or simply called Faraday equation) and Maxwell-Faraday equation. I found that the Faraday equation describes not only Maxwell-Faraday equation, but also magnetic Lorentz...
23. ### Magnetic flux and current directions of transformer

Hello. Let's take a transformer picture first. The basic equation explaining how the transformer work is the equation of Faraday's law of induction. \begin{array}{*{20}{c}} {{V_P} = - {N_P}\frac{{d{{\rm{\Phi }}_B}}}{{dt}}\;\;\;\;\left( 1 \right).}\\ {{V_S} = - {N_S}\frac{{d{{\rm{\Phi...
24. ### Some confusion of Faraday's law of induction.

Hello. Thank you for a quick reply! Well..in 2nd answer, how to derive the original Faraday equation from the differential form of MF (Maxwell-Faraday) Equation? Applying stokes' theorem to this MF equation only gives MF equation in an integral form where ∂/∂t is inside the integral, while the...
25. ### Some confusion of Faraday's law of induction.

Hello. I have several confusions regarding Faraday's law of induction. EMF = \int_{}^{} {\vec E \cdot d\vec l} = - \frac{{d\Phi }}{{dt}} = - \frac{d}{{dt}}\int_{}^{} {\vec B \cdot d\vec S} . It means that If the magnetic flux Φ through the closed conducting loop changes in time, electric...
26. ### How does an equivalent impedance consume a real power?

Please never mind. "Pure active" just means that the power on Zeq has no reactive power, it only has an active power. The original sentence I made was right. I was trying to emphasize a difference between an active power and a reactive power. Thanks for giving me some advice. I'll consider...
27. ### How does an equivalent impedance consume a real power?

Hello. Thanks for giving comments. I think I need to think this problem more carefully, before asking further and further. However, in order to start right reasoning, I need to confirm one thing: In impedance matching by adjusting CT and CL so that Zeq = RS, a power dissipated in Zeq is P1 =...
28. ### How does an equivalent impedance consume a real power?

Hello. I'm sorry but phase? Do you want me to write phase of ..impedance? I'm talking about general case so a specific phase is not relevant. And what do you mean > and < ?
29. ### How does an equivalent impedance consume a real power?

Hello. Thanks for giving a quick answer:) I'm sorry but I'm afraid I couldn't get your point yet. I know how the transformer works and it seems that you're equating any complex network with a load ZL = RL + iXL to some ideal transformer with a load RL in its secondary side. I don't know how...
30. ### How does an equivalent impedance consume a real power?

Hello. Please looks at the attached image first. The left image is LCC impedance matching network (one of T-type impedance matching networks) and the right is the corresponding equivalent circuit when CT and CL are adjusted such that an equivalent impedance of the sub-circuit surrounded by...